TJFI7BRSIT7 


BIRD'S-EYE  VIEW  OF  MARBLE  CANON  FROM  THE  VERMILION  CLIFFS,  NEAR  THE  MOUTH  OF  THE 
PARIA.  In  the  distance  the  Colorado  River  is  seen  to  turn  to  the  west,  where  its  gorge  divides 
the  Twin  Plateaus.  On  the  right  are  seen  the  Eastern  Kaibab  Displacements  appearing  as 
folds,  and  farther  in  the  distance  as  faults. 


ELEMENTS 

OF    G-E  OLOG-Y 


A   TEXT-BOOK  FOR  COLLEGES  AND  FOR 
THE  GENERAL   READER 


BY 


JOSEPH  LE  CONTE 


AUTHOR  OP  RELIGION  AND  SCIENCE 
SIGHT  :    AN   EXPOSITION  OF  THE  PRINCIPLES  OP  MONOCULAR  AND  BINOCULAR  VISION 

EVOLUTION  IN  ITS  RELATION  TO  RELIGIOUS  THOUGHT,   ETC. 
AND  PROFESSOR  OF  GEOLOGY  AND  NATURAL  HISTORY    IN  THE  UNIVERSITY  OF  CALIFORNIA 


REVISED  AND  ENLARGED 
WITH  NEW  PLATES  AND  ILLUSTRATIONS 


NEW    YORK 

D.    APPLETON    AND    COMPANY 
1891 


,5*11465" 


COPYRIGHT,  1877,  1882,  1891, 
Br  D.  APPLETON  AND  COMPANY. 


0? 

UFI7BRSIT7 


PREFACE  TO   THE   THIRD   EDITION. 


THE  progress  of.  American  geology  is  so  rapid — important  new  dis- 
coveries follow  one  another  in  so  quick  succession — that  any  text-book, 
however  carefully  prepared,  must  require  large  revision  in  a  very  few 
years.  In  the  present  edition  the  alterations,  by  omission,  by  modifi- 
cation, and  especially  by  additions,  are  so  numerous  and  so  great  that 
it  was  found  necessary  to  reset  the  whole  work,  and  to  rewrite  a  large 
portion.  I  have  tried  to  do  this  without  enlarging  to  any  considerable 
extent  the  size  of  the  book 

The  most  important  changes  are  the  following :  In  Part  I  I  have 
made  some  additions  to  the  discussion  of  river-agencies,  especially  in 
regard  to  the  mutual  relations  of  erosion  and  sedimentation ;  and  to 
rivers  as  indicators  of  crust-movements.  On  the  subject  of  earth- 
quakes I  have  left  out  the  general  discussion  of  waves,  as  belonging 
strictly  to  physics,  and  have  given  more  fully  the  subject  of  seismom- 
etry.  On  coral  reefs  I  have  given  a  brief  account  of  the  theory  of 
Murray  on  the  formation  of  atolls  and  barriers.  I  have  stricken  out 
entirely  the  section  on  Geographical  Distribution  of  Organisms,  as  be- 
longing either  to  Biology  or  to  Physical  Geography,  and  to  make  room 
for  more  strictly  geological  matters  pressing  for  recognition.  But  I 
have  made  compensation  for  this  by  a  much  fuller  discussion,  in  Part 
III,  of  the  geological  causes  of  present  distribution. 

In  Part  II  the  structure  and  position  of  stratified  rocks  are  largely 
rewritten,  and  some  changes  introduced.  The  discussion  on  mineral 
veins  has  been  somewhat  enlarged,  and  many  changes  introduced  in 
the  discussion  of  faults  and  their  causes.  The  section  on  mountains 
hag  been  entirely  rewritten,  the  order  of  presentation  changed,  and 
new  matter  introduced. 

In  Part  III  the  changes  are  still  more  extensive,  and  the  law  of 


IV  PREFACE   TO   THE   THIRD   EDITION. 

evolution  is  kept  more  prominently  in  view.  The  subjects  of  Devonian 
fishes  and  of  Carboniferous  Conifers  are  rewritten,  and  the  origin  of 
birds  and  mammals  more  fully  discussed.  In  the  Cretaceous,  the  Co- 
manche  series  of  Hill  and  the  Potomac  series  of  McGee  are  discussed, 
and  figures  of  characteristic  forms  given.  The  Laramie,  on  account  of 
its  peculiar  interest  as  a  transitional  period,  is  treated  separately,  and 
figures  of  characteristic  forms  are  given.  In  the  Tertiary  the  subject 
of  the  mammalian  fauna  of  America  is  mostly  rewritten,  and. the  genesis 
of  existing  orders,  families,  genera,  etc.,  more  fully  discussed.  In  the 
Quaternary  the  evidences  of  continental  elevation,  the  existence  of  an 
ice-sheet,  with  its  terminal  moraine,  and  the  Great  Lakes  formed  during 
its  retreat,  are  more  fully  given.  The  Quaternary,  on  the  west  side  of 
the  continent,  is  rewritten,  the  order  of  presentation  changed,  and  new 
matter  introduced,  especially  the  evidences  of  continental  elevation 
and  of  rejuvenescence  of  the  rivers  by  Sierra  elevation.  Under  causes 
of  glacial  climate,  I  give  greater  prominence  than  before  to  geographi- 
cal changes.  Changes  of  climate  and  of  Physical  Geography,  as  the 
cause  of  the  present  distribution  of  organisms,  are  somewhat  fully  dis- 
cussed, and  several  examples  given  and  explained.  In  the  chapter  on 
the  Psychozoic  era  the  most  recent  discoveries  of  human  remains  and 
implements,  both  in  Europe  and  America,  are  given,  and  their  signifi- 
cance discussed. 

To  the  geologists  of  America,  who  have  freely  helped  and  encour- 
aged me,  and  especially  to  gentlemen  connected  with  the  United  States 
Geological  Survey,  I  take  this  opportunity  of  acknowledging  my  deep 
indebtedness. 

BERKELEY,  CAL,.  January,  1891. 


PKEFACE   TO   THE   FIRST  EDITION. 


IN  preparing  the  following  work  I  have  not  attempted  to  make  an 
exhaustive  manual  to  be  thumbed  by  the  special  student ;  for,  even  if 
I  felt  able  to  write  such  a  work,  Prof.  Dana's  is  already  in  the  field, 
and  is  all  that  can  be  desired  in  this  respect.  I  have  endeavored  only 
to  present  clearly  to  the  thoroughly  cultured  and  intelligent  student 
and  reader  whatever  is  best  and  most  interesting  in  Geological  Science. 
I  have  attempted  to  realize  what  I  conceive  to  be  comprised  in  the 
word  elements,  as  contradistinguished  from  manual.  I  have  attempted 
to  give  a  really  scientific  presentation  of  all  the  departments  of  the 
wide  field  of  geology,  at  the  same  time  avoiding  too  great  multiplica- 
tion of  detail.  I  have  desired  to  make  a  work  which  shall  be  both 
interesting  and  profitable  to  the  intelligent  general  reader,  and  at  the 
same  time  a  suitable  text-book  for  the  higher  classes  of  our  colleges. 
In  the  selection  of  material  and  mode  of  presentation  I  have  been 
guided  by  long  experience,  as  to  what  it  is  possible  to  make  interesting 
to  a  class  of  young  men,  somewhat  advanced  in  general  culture  and 
eager  for  knowledge,  but  not  expecting  to  become  special  geologists. 
In  a  word,  I  have  tried  to  give  such  knowledge  as  every  thoroughly 
cultured  man  ought  to  have,  and  at  the  same  time  is  a  suitable  founda- 
tion for  the  further  prosecution  of  the  subject  to  those  who  so  desire. 
The  tvork  is  the  substance  of  a  course  of  lectures  to  a  senior  class, 
organized,  compacted,  and  disencumbered  of  too  much  detail,  by  re- 
presentation for  many  successive  years,  and  now  for  the  first  time 
reduced  to  writing. 

Most  text-books  now  in  use  in  this  country  are,  in  rny  opinion, 
either  too  elementary  on  the  one  hand,  or  else  adapted  as  manuals  for 
the  specialists  on  the  other.  I  wish  to  fill  this  gap — to  supply  a  want 
felt  by  many  intelligent  students  and  general  readers,  who  desire  a 


vi  PREFACE   TO   THE   FIRST   EDITION. 

really  scientific  general  knowledge  of  geology.  Lyell's  Elements 
comes  nearest  to  supplying  this  want ;  but  there  are  two  objections  to 
this  admirable  work :  1.  The  principles  (dynamical  geology)  are  sepa- 
rated from  the  elements  (structural  and  historical  geology),  and  treated 
in  a  different  work ;  2.  Its  treatment  of  American  geology  is  of  course 
meager. 

I  have  treated  several  subjects  in  dynamical  and  structural  geology 
— e.  g.,  rivers,  glaciers,  volcanoes,  geysers,  earthquakes,  coral-reefs, 
slaty  cleavage,  metamorphism,  mineral  veins,  mountain-chains,  etc. — 
more  fully  than  is  common.  I  feel  hopeful  that  many  geologists  and 
physicists  will  thank  me  for  so  doing.  I  am  confident  that  I  give 
somewhat  fairly  the  present  condition  of  science  on  these  subjects. 

In  the  historical  part  I  have  found  much  more  difficulty  in  being 
scientific  without  being  tiresome,  and  in  being  interesting  without 
being  superficial  and  wordy.  I  have  attempted  to  accomplish  this  diffi- 
cult task  by  making  evolution  the  central  idea,  about  which  many  of 
the  facts  are  grouped.  I  have  tried  to  keep  this  idea  in  view,  as  a 
thread  running  through  the  whole  history,  often  very  slender — some- 
times, indeed,  invisible — but  reappearing  from  time  to  time  to  give 
consistency  and  meaning  to  the  history. 

If  this  work  have  any  advantage  over  others  already  before  the 
public,  it  is  chiefly  in  the  two  points  mentioned  above,  viz.,  in  a  fuller 
presentation  of  some  subjects  in  dynamical  and  structural  geology,  and 
in  the  attempt  to  keep  evolution  in  view,  and  to  make  it  the  central 
idea  of  the  history.  Another  advantage,  I  believe,  is  that  it  does  not 
seek  to  compete  with  the  best  works  now  before  the  public,  but  occu- 
pies a  distinct  field  and  supplies  a  distinct  want. 

I  have  confined  myself  mostly,  though  not  entirely,  to  American 
geology,  especially  in  giving  the  distribution  of  the  rocks  and  the 
physical  geography  of  the  different  periods.  In  only  one  case  have  I 
made  American  geology  subordinate,  viz.,  in  the  Jura-Trias  period,  and 
that  only  because  of  the  meagerness  of  the  record  of  this  period  in  this 
country. 

In  a  science  so  comprehensive  and  many-sided  as  geology,  it  is 
simply  impossible,  as  every  teacher  knows,  to  avoid  anticipations  in 
one  part  of  what  strictly  belongs  to  a  subsequent  part.  It  is  for  this 
reason  that  the  order  of  presentation  of  the  different  departments,  and 
of  the  various  subjects  under  each  department,  is  so  different  in  the 


PREFACE   TO  THE  FIRST  EDITIOX.  vii 

hands  of  different  writers.  The  order  which  I  have  adopted  I  know  is 
not  free  from  objection  on  this  score,  but  it  seemed  to  me,  on  the 
whole,  the  best. 

In  preparing  the  work  I  have,  of  course,  drawn  largely  from  many 
sources,  both  text-books  and  works  of  original  research ;  for  whatever 
of  merit  there  be  in  a  work  of  this  kind  must  consist  not  so  much  in 
the  novelty  of  the  matter  as  in  the  selecting,  grouping,  and  presenta- 
tion. Such  obligations  are  acknowledged  in  the  pages  of  the  work. 
I  can  not  forbear,  however,  making  here  a  special  acknowledgment  of 
my  indebtedness,  in  the  historical  part,  to  the  invaluable  Manual  of 
Prof.  Dana.  I  must  also  acknowledge  especial  indebtedness  to  Profs. 
Marsh,  Newberry,  and  Cope,  and  the  geologists  and  paleontologists  of 
the  United  States  Surveys,  in  charge  of  Prof.  Hayden  and  Lieutenant 
Wheeler,  not  only  for  valuable  materials,  but  also  for  much  personal 
aid. 


CONTENTS. 


INTRODUCTORY. 

PAGE 

DEFINITION  OF  GEOLOGY,  AND  ITS  DEPARTMENTS 1-2 

GEOLOGY,  1 ;  Principal  Departments,  2 ;  Order  of  Treatment,  2. 


PART  I. 

D  YNA  MIC  AL     GEOLOGY. 

CHAPTER  I. 
ATMOSPHERIC  AGENCIES .     3-8 

Soils,  4 ;  General  Explanation,  6 ;  Granite,  Gneiss,  Volcanic  Rocks,  etc.,  7 ;  Lime- 
stone, 7 ;  Sandstones,  7 ;  Slate,  7.  MECHANICAL  AGENCIES  OF  THE  ATMOSPHERE. 
—Frost,  8 ;  Winds,  8. 

CHAPTER  II. 
AQUEOUS  AGENCIES        ...  ...  .     9-82 

SECTION  1.  RIVERS,  9.  Erosion  of  Rain  and  Rivers,  9 ;  Hydrographical  Basin,  10 ; 
Rate  of  Erosion  of  Continents,  10 ;  Law  of  Variation  of  Erosive  Power,  11.  Ex- 
amples of  Great  Erosion  now  going  on :  Waterfalls,  12 ;  Niagara,  General  Descrip- 
tion, 12 ;  Recession  of  the  Falls,  12 ;  Other  Falls,  13 ;  Time  necessary  to  excavate 
Niagara  Gorge,  14 ;  Ravines,  Gorges,  Canons,  15  ;  Time,  17.  Transportation  and 
Distribution  of  Sediments,  18;  Experiments,  18;  Law  of  Variation,  19:  1.  Re- 
lation of  Velocity  to  Erosion  and  Sedimentation,  21 ;  illustrated  by  Colorado  and 
Platte  Rivers,  21.  2.  Rivers  seek  their  Base-Level,  21 ;  Rivers  as  Indicators  of 
Crust-Movements,  22.  3.  Stratification,  22.  4.  Winding  Course  of  Rivers,  23. 
5.  Flood-Plain  Deposits,  24 ;  River-Swamp,  24 ;  Natural  Lev6es,  25 ;  Artificial 
Levies,  25  6.  Deltas,  26;  Process  of  Formation,  28;  Rate  of  Growth,  29; 
Acre  of  River-Deposits,  30.  7.  Estuaries,  31;  Mode  of  Formation,  31 ;  Deposits 
in  Estuaries,  32.  8.  Bars,  32 ;  Improvement  of  Bars,  33. 

SECTION  2.  OCEAN. —  Waves  and  Tides. — Waves,  34  ;  Tides,  35 ;  Examples  of  the 
Action  of  Waves  and  Tides,  35  ;  Transporting  Power,  38 ;  Deposits,  39  ;  Oceanic 
Currents,  39;  Theory  of  Oceanic  Currents,  39;  Application,  41;  Geological 
Agency  of  Oceanic  Currents,  42  ;  Submarine  Banks,  43  ;  Land  formed  by  Ocean 
Agencies,  44. 

SECTION  3.  ICE,  45.     Glaciers. — Definition,  45  ;  Necessary  Conditions,  4G ;  Rami- 


X  CONTENTS. 

PAGE 

fications  of  Glaciers,  46;  Motion  of  Glaciers,  48;  Advance  and  Retreat — 
Graphic  Illustration,  48  ;  Line  of  the  Lower  Limit  of  Glaciers,  49  ;  General  De- 
scription, 50 ;  Earth  and  Stones,  etc.,  53.  Moraines,  54.  Glaciers  as  a  Geologi- 
cal Agent,  55  ;  Erosion,  55  ;  Transportation,  57  ;  Deposit — Balanced  Stones,  57 ; 
Material  of  the  Terminal  Moraine,  57 ;  Evidences  of  Former  Extension  of  Gla- 
ciers, 58  ;  Glacial  Lakes,  58.  Motion  of  Glaciers  and  its  Laivs. — Evidences  of 
Motion,  59  ;  Laws  of  Glacier-Motion,  59.  Theories  of  Glacier-Motion,  01.  Vis- 
cosity Theory  of  Forbes. — Statement  of  the  Theory,  61 ;  Argument,  61.  Regda- 
tion  Theory  of  Tyndall,  63 ;  Regelation,  64  ;  Application  to  Glaciers,  64  ;  Compari- 
son of  the  Two  Theories,  65  ;  Croll's  Theory,  65  ;  Thomson's  Theory,  66.  Struct- 
ure of  Glaciers,  66 ;  Veined  Structure,  66  ;  Fissures,  67.  Theories  of  Structure. 
— Fissures,  67 ;  Veined  Structure,  68  ;  Physical  Theory  of  Veins,  69.  Floating 
Ice — Icebergs,  70 ;  General  Description,  71 ;  Icebergs  as  a  Geological  Agent — 
Erosion,  72 ;  Deposits,  72.  Shore-Ice,  72.  Comparison  of  the  Different  Forms 
of  the  Mechanical  Agencies  of  Water,  73. 

SECTION  4.  CHEMICAL  AGENCIES  OF  WATER. — Subterranean  Waters,  Springs,  etc., 
74 ;  Springs,  74 ;  Artesian  Wells,  75  ;  Chemical  Effects  of  Subterranean  Waters, 
76 ;  Limestone  Caves,  76.  Chemical  Deposits  in  Springs. — Deposits  of  Carbon- 
ate of  Lime,  77 ;  Explanation,  77  ;  Kinds  of  Materials,  78 ;  Deposits  of  Iron,  79 ; 
Deposits  of  Silica,  79  ;  Deposits  of  Sulphur  and  Gypsum,  79.  Chemical  Depos- 
its in  Lakes. — Salt  Lakes  and  Alkaline  Lakes,  79 ;  Conditions  of  Salt-Lake  For- 
mation, 80 ;  Deposits  in  Salt  Lakes,  81.  Chemical  Deposits  in  Seas,  82. 

CHAPTER   III. 
IGNEOUS  AGENCIES 82-140 

SECTION  1.  INTERIOR  HEAT  OF  THE  EARTH. — Stratum  of  Invariable  Temperature,  83  ; 
Increasing  Temperature  of  the  Interior  of  the  Earth,  84 ;  Constitution  of  the 
Earth's  Interior,  84 :  1.  Rate  of  Increase  not  uniform,  85  ;  2.  Fusing- Point  not 
the  same  for  all  Depths,  86  ;  Astronomical  Reasons,  87 ;  Most  Probable  View,  87. 

SECTION  2.  VOLCANOES.— Definition,  87  ;  Size,  Number,  and  Distribution,  88  ;  Phe- 
nomena of  an  Eruption,  89 ;  Monticules,  90 ;  Materials  erupted,  90 ;  Stones,  90  ; 
Lava,  90;  Liquidity  of  Lava,  90;  Physical  Conditions  of  Lava,  91 ;  Classifica- 
tion of  Lavas,  92 ;  Gas,  Smoke,  and  Fiame,  93 ;  Kinds  of  Volcanic  Cones,  93  ; 
Mode  of  Formation  of  a  Volcanic  Cone,  93 ;  Comparison  between  a  Volcanic 
Cone  and  an  Exogenous  Tree,  96  ;  Estimate  of  the  Age  of  Volcanoes,  97.  Theory 
of  Volcanoes,  97 ;  Force,  97 ;  The  Heat,  98 ;  Internal  Fluidity  Theory,  98 ;  Ob- 
jections, 98;  Chemical  Theory,  99;  Recent  Theories,  100;  Aqueo-igneous  The- 
ory, 100;  Fisher's  Theory,  100;  Mechanical  Theory,  100;  Prestwich's  Theory, 
101.  Subordinate  Volcanic  Phenomena,  101;  General  Explanation,  101.  Gey- 
sers, 101 ;  Description,  101 ;  Phenomena  of  an  Eruption,  103  ;  Yellowstone  Gey- 
sers, 103;  Theories  of  Geyser-Eruption,  106;  Mackenzie's  Theory,  106;  Bun- 
sen's  Investigations,  107 ;  Theory  of  Geyser-Eruption — Principles,  108  ;  Appli- 
cation to  Geysers,  108;  Bunsen's  Theory  of  Geyser-Formation,  110. 

SECTION  3.  EARTHQUAKES,  111;  Frequency,  111;  Connection  with  other  Forms  of 
Igneous  Agency,  111 ;  Ultimate  Cause  of  Earthquakes,  113;  Proximate  Cause, 
114;  Application  to  Earthquakes,  114;  Experimental  Determination  of  the  Ve- 
locity of  the  Spherical  Wave,  116  ;  Character  of  the  Wave,  116;  Explanation  of 
Earthquake-Phenomena,  117;  Verticose  Earthquakes,  120;  Explanation,  120; 
Minor  Phenomena,  122.  Earthquakes  originating  beneath  the  Ocean,  125  ;  Great 
Sea-Wave,  125  ;  Examples  of  the  Sea-Wave,  126.  Depth  of  Earthquake-Focus, 


CONTENTS.  xi 

PAGE 

123;  Seismographs,  128;  The  Determination  of  the  Epicentrura,  130;  Deter- 
mination of  the  Focus — Examples,  131 ;  Effect  of  the  Moon  on  Earthquake-Oc- 
currence, 132  ;  Relation  of  Earthquake-Occurrence  to  Seasons  and  Atmospheric 
Conditions,  133. 

SECTION  4.  GRADUAL  ELEVATION  AND  DEPRESSION  OF  THE  EARTH'S  CBUST,  1 33 ;  Ele- 
vation or  Depression  during  Earthquakes,  134 ;  Movements  not  connected  with 
Earthquakes— South  America,  134;  Italy,  134;  Scandinavia,  185;  Greenland, 
136 ;  Deltas  of  Large  Rivers,  136  ;  Southern  Atlantic  States,  137 ;  Pacific  Ocean, 
137;  River-beds  as  Indicators  of,  137.  Theories  of  Elevation  and  Depression, 
138;  Babbagc's  Theory,  138;  Herschel's  Theory,  139;  General  Theory,  139. 

CHAPTER  IV. 
ORGANIC  AGENCIES  X 140-161 

SECTION  1.  VEGETABLE  ACCUMULATIONS. — Peat-Bogs  and  Peat-Swamps. — Descrip- 
tion, 140;  Composition  and  Properties  of  Peat,  140;  Mode  of  Growth,  141; 
Rate  of  Growth,  142;  Conditions  of  Growth,  142;  Alternation  of  Peat  with 
Sediments,  143.  Drift-Timber,  143. 

SECTION  2.  BOG-!RON  ORE,  143.  Conditions  of  Deposit  and  Geological  Applica- 
tion, 144. 

SECTION  8.  LIME  ACCUMULATIONS — Coral  Reefs  and  Islands, — Interest  and  Im- 
portance, 145;  Coral  Polyp,  145;  Compound  Coral,  or  Corallum,  145;  Coral 
Forests,  145;  Coral  Reef,  146;  Coral  Islands,  146  ;  Conditions  of  Coral-Growth, 
147;  Pacific  Reefs,  147;  Fringing  Reefs,  147;  Barrier  Reefs,  148;  Circular 
Reefs,  or  Atolls,  148 ;  Small  Atolls  and  Lagoonless  Islands,  149.  TJieories  of 
Barrier  and  Circular  Reefs,  150;  Crater  Theory,  150;  Objections,  150;  Dar- 
win's Subsidence  Theory,  150;  Proofs,  151;  Murray's  Theory,  152;  Area  of 
Land  lost,  153  ;  Amount  of  Vertical  Subsidence,  153  ;  Rate  of  Subsidence,  154 ; 
Time  involved,  155;  Geological  Application,  155;  Reefs  of  Florida,  156;  De- 
scription of  Florida,  156;  General  Process  of  Formation,  157;  History  of 
Changes,  157;  Mangrove  Islands,  158;  Florida  Reefs  compared  with  other 
Reefs,  159;  Differences — 1.  Continuous  land-making.  2.  Barriers  without 
Subsidence,  160 ;  Probable  Agency  of  the  Gulf  Stream.  160  Shell-Deposits, 
160;  Molluscous  Shells,  161 ;  Microscopic  Shells,  161. 


PART  II. 

STRUCTURAL     GEOLOGY. 

CHAPTER  I. 

GENERAL  FORM  AND  STRUCTTRE  OF  THE  EARTH     ....     163-170 
1.  Form  of  the  Earth,  163.     2.  Density  of  the  Earth,  165.     3.   The  Crust  of  the 
Earth,  166;  Means  of  Gaological  Observation,  166.     4.   General  Surface  Con- 
figuration of  the  Earth,  167  ;  Cause  of  Land-Surfaces  and  Sea-Bottoms,  167; 
Laws  of  Continental  Form,  169.     Rocks,  170;  Classes  of  Rocks,  170. 

CHAPTER  II. 

STRATIFIED  OR  SEDIMENTARY  ROCKS 170-201 

SECTION  1.  STRUCTURE  AND  POSITION. — Stratification,  170;  Extent  and  Thickness, 
171 ;  Kinds  of  Stratified  Rocks,  171 ;  I.  Stratified  Rocks  are  more  or  less  Con- 


xii  CONTENTS. 

PAGE 

solidated  Sediments,  172;  Cause  of  Consolidation,  172;  II.  Stratified  Rocks 
have  been  gradually  deposited,  173  ;  III.  Stratified  Rocks  were  originally  nearly 
horizontal,  173;  Elevated,  Inclined,  and  Folded  Strata,  174;  Dip  and  Strike, 
176;  Anticlines  and  Synclines,  178;  Monoclines,  178;  Conformity  and  Uncon- 
formity, 179;  Geological  Formation,  181.  Cleavage  Structure,  181;  Cause  of 
Sharpe's  Mechanical  Theory,  183;  Physical  Theory,  185;  Sorby's  Theory,  185; 
Tyndall's  Theory,  186;  Geological  Application,  187.  Nodular  or  Concretionary 
Structure,  188;  Cause,  189;  Forms  of  Nodules,  189;  Kinds  of  Nodules  found 
in  Different  Strata,  190.  Fossils:  Their  Origin  and  Distribution,  190;  The 
Degrees  of  Preservation  are  very  various,  191;  Theory  of  Petrifaction,  192. 
Distribution  of  Fossils  in  the  Strata,  194:  1.  Kind  of  Rock,  194  ;  2.  The  Coun- 
try where  found,  195  ;  3.  The  Age,  195 ;  Geological  Fauna  and  Era,  195. 
SECTION  2.  CLASSIFICATION  OP  STRATIFIED  ROCKS,  197;  Methods:  1.  Order  of 
Superposition,  197 ;  2.  Lithological  Character,  198 ;  3.  Comparison  of  Fossils, 
198;  Manner  of  constructing  a  Geological  Chronology,  199;  Table  of  Main 
Divisions,  200. 

CHAPTER   III. 

UNSTRATIFIED  OR  IGNEOUS  ROCKS 201-219 

Characteristics,  201 ;  General  Origin,  201 ;  Mode  of  Occurrence,  201 ;  Extent  on 
the  Surface,  202;  Classification  of  Igneous  Rocks,  202. 

I.  PLUTONIC  OR  MASSIVE  ROCKS,  203  ;  General  Appearance,  203  ;  Principal  Kinds 
—Granite,  203 ;  Syenite,  203 ;  Diorite,  203 ;  Diabase,  204 ;  Two  Sub-Groups, 
Acidic  and  Basic,  204 ;  Mode  of  Occurrence,   204 ;  Intermediate  Scries,   205 ; 
Kinds,  206. 

II.  VOLCANIC  OR  ERUPTIVE  ROCKS,  206;  Texture  and  Appearance,  206;  Ph}sical 
Conditions,  206 ;  Mineral  Composition  and  Sub-Groups,  207 ;  Principal  Kinds, 
207  ;  Table  showing  Principal  Kinds  of  all  Classes  of  Igneous  Rocks,  208  ;  Modes 
of  Eruption,  208 ;  Modes  of  Occurrence,  209 ;  Dikes,  209 ;  Effect  of  Dikes  on 
Intersected  Strata,  210;  Lava-Sheets,  210;  Intercalary  Beds  and   Laccolites, 
211 ;  Age— how  determined,  212.     Of  Certain  Structures  found  in  many  Erup- 
tive Rocks,   212;  Columnar  Structure,    212;  Direction  of  the  Columns,  213; 
Cause  of  Columnar  Structure,  214;  Volcanic  Conglomerate  and  Breccia,  214;     ; 
Amygdaloid,  215.     Some  Important  General   Questions  connected  with  Igneous 
Rocks,  215  :  1.  Origin  of  Igneous  Rocks,  215.    2.  Other  modes  of  Classification, 
216.  3.  Richthofen's  Classification  of  Tertiary  Eruptions,  218 ;  Judd's  Views,  218. 

CHAPTER  IV. 
METAMORPHIC  ROCKS 219-226 

Origin,  219;  Position,  219,  Extent  on  the  Earth-Surface,  219;  Principal  Kinds, 
220 ;  Theory  of  Metamorphism,  221  ;  Effect  of  Water,  221 ;  Alkali,  222 ; 
Pressure,  222 ;  Application,  222  ;  Crushing,  223  ;  Explanation  of  Associated 
Phenomena,  223  ;  Origin  of  Granite,  223. 


CHAPTER  V.  PAGE 

STRUCTURE  COMMON  TO  ALL  ROCKS 226-273 

SECTION  1.  JOINTS  AND  FISSURES. — Joints,  226  ;  Fissures  or  Fractures,  227  ;  Cause, 
228;  Faults,  228;  Kinds— Law  of  Slip,  231;  Explanation  of  Direction  of 
Slip,  332. 


CONTENTS. 

PAGE 

SECTION  2.  MINERAL  VEINS,  234 ;  Kinds,  234 ;  Characteristics  of  Fissure- Veins, 
235 ;  Metalliferous  Veins,  235 ;  Contents,  235  ;  Ribboned  Structure,  236 ;  Ir- 
regularities, 237  ;  Age,  238  ;  Surface-Changes,  238  ;  Cupriferous  Veins,  239  ; 
Plumbifercus  Veins,  240;  Auriferous  Quartz- Veins,  240;  Placer-Mines,  240. 
Some  Important  Laws  affecting  the  Occurrence  and  the  Richness  of  Metalliferous 
Vei)is,  241.  Theory  of  Metalliferous  Veins,  243  ;  Outline  of  the  Most  Probable 
Theory,  243  ;  Vein-Stuffs  explained,  243  ;  Metallic  Ores,  245  ;  Auriferous  Veins 
of  California,  247  ;  Illustrations  of  the  Law  of  Circulation,  249. 

SECTION  3.  MOUNTAINS  :  THEIR  ORIGIN  AND  STRUCTURE,  250 ;  Definition  of  Terms 
— Mountain-System — Mountain-Range — Ridge — Peak.  Mountain.  Origin,  251  ; 
Mountain- Structure,  252;  Proof  of  Lateral  Pressure:  1.  By  Folded  Structure, 
254 ;  2.  By  Slaty  Cleavage,  255  ;  Modifications  of  the  Ideal :  1.  By  Fracture 
and  Slipping,  256 ;  2.  By  Metamorphisra  ;  3.  By  Erosion  Mountains  are  Lines 
of  Thick  Sediments,  257  ;  Mountain-Ranges  were  Marginal  Sea-Bottoms,  258. 
Illustrated  by — 1.  Appalachian,  2.  Sierra,  259  ;  3.  Coast  Range  ;  4.  Wahsatch; 
5.  Alps,  260 ;  Why  along  Lines  of  Thick  Sediments,  History  of  a  Mountain- 
Range,  261 ;  Slowness  of  Mountain-Growth,  261 ;  Age  of  Mountains,  261 ;  Other 
Associated  Phenomena  explained,  262.  1.  Fissures,  Dikes,  Lava-Floods;  2. 
Volcanoes,  263  ;  3.  Mineral  Veins  ;  4.  Faults  and  Earthquakes.  Cause  of  Lat- 
eral Pressure  ;  Most  Probable  View,  264  ;  Another  Type  of  Mountains,  Mono- 
clinah,  many  Mountains  combine  the  Two  Modes,  265,  e.  g.,  Sierra,  Wahsatch ; 
Origin  of  Basin-Structure,  266  ;  Mountain- Sculpture,  266 ;  Amount  of  Erosion, 
267 ;  Sculptural  Forms :  1.  In  Horizontal  Strata ;  2.  In  Gently  Undulating 
Strata,  268  ;  Synclinal  Ridges  how  formed  ;  3.  Strongly  Folded  and  Highly  In- 
clined Strata,  269;  Hog-backs;  4.  Gently  Inclined  Strata,  270;  Tables  and 
Cliffs,  271  ;  Migration  of  Divides,  272  ;  5.  Mctamorphic  and  Granitic  Rocks;  6. 
Kind  of  Agent — Ice  vs.  Water. 

CHAPTER   VI. 

DENUDATION,  OR  GENERAL  EROSION       ,  .  .  .     273-279 

Agents  of  Denudation,  273 ;  Amount  of  Denudation,  274  ;  Average  Erosion,  275 ; 
Estimate  of  Geological  Times,  276. 


PART  HI. 

HISTORICAL    GEOLOGY;    THE  HISTORY  OF   THE  EVOLUTION  OF 
EARTH-STRUCTURE  AND   OF  THE  ORGANIC  KINGDOM. 

CHAPTER   I. 

GENERAL  PRINCIPLES 279-285 

General  Laws  of  Evolution,  279 ;  Great  Divisions  and  Subdivisions  of  Time — Eras, 
2S1 ;  Ages,  282 ;  Subdivisions,  283 ;  Order  of  Discussion,  283  ;  Prehistoric  Eras, 
285. 

CHAPTER   II. 

LAURENTIAN  SYSTEM  OF  ROCKS  AND  ARCHAEAN  ERA       .        .         .     285-289 
General  Description,  285  ;  Rocks,  286  ;  Area  in  North  America,  287  ;  Physical  Ge- 
ography of  Archaean  Times,  287 ;  Time  represented,  288  ;  Evidences  of  Life,  288. 


xiv  CONTEXTS. 

PAGE 

CHAPTER  III. 
PRIMARY  OR  PALAEOZOIC  SYSTEM  OF  ROCKS  AND  PALEOZOIC  ERA.     289-413 

General  Description,  289  ;  Rocks — Thickness,  etc.,  290 ;  Area  in  the  United  States, 
291 ;  Geological  Map  of  the  United  States,  291  ;  Physical  Geography  of  the  Ameri- 
can Continent,  292;  Subdivisions,  293;  The  Interval,  294;  Importance,  295. 

SECTION  1.  SILURIAN  SYSTEM:  AGE  OF  INVERTEBRATES. — The  Rock  System,  296; 
Subdivisions,  296  ;  Character  of  the  Rocks,  296  ;  Area  in  America,  296  ;  Physi- 
cal Geography,  297 ;  Primordial  Beach  and  its  Fossils,  298 ;  General  Remarks 
on  First  Distinct  Fauna,  301.  General  Life-System  of  the  Silurian  Age,  302  ; 
Plants,  304;  Animals,  304;  Protozoans,  304 ;  Radiates,  Corals,  304 ;  Hydrozoa, 
308;  Polyzoa,  309;  Echinoderms,  309;  Mollusks,  313;  General  Description  of 
a  Brachiopcd,  314  ;  Lamellibranchs,  316  ;  Gasteropods,  316  ;  Cephalopods,  317  ; 
Articulates,  320 ;  Crustacea,  320 ;  General  Description  of  a  Trilobite,  320 ;  Af- 
finities of  Trilobites,  325 ;  Eurypterids,  326 ;  Anticipations  of  the  Next  Age, 
326  ;  Land-Plants,  Insects,  Fishes,  326. 

SECTION  2.  DEVONIAN  SYSTEM  AND  AGE  OF  FISHES,  327 ;  Area  in  United  States,  327 ; 
Physical  Geography,  327;  Subdivision  into  Periods,  328.  Life-System  of  Devo- 
nian Age — Plants,  328  ;  General  Remarks  on  Devonian  Land- Plants,  329  ;  Ani- 
mals, 332  ;  Radiates,  332 ;  Brachiopods,  332 ;  Cephalopods,  333  ;  Crustacea,  333  ; 
Insects,  334  ;  Fishes,  334 ;  Examples  of  Devonian  Fishes,  335  ;  Classification  of 
Devonian  Ganoids,  338  ;  Nearest  Living  Allies,  339  ;  General  Characteristics  of 
Devonian  Fishes,  340 ;  Devonian  Fishes  were  Generalized  Types,  342  ;  Bearing 
of  these  Facts  on  the  Question  of  Evolution,  343  ;  Suddenness  of  Appearance,  344. 

SECTION  3.  CARBONIFEROUS  SYSTEM  :  AGE  OF  ACROGENS  AND  AMPHIBIANS. — Retro- 
spect, 345  ;  Subdivisions  of  the  Carboniferous  System  and  Age,  345.  Carbonif- 
erous Proper— Rock- System  or  Coal-Measures,  346  ;  The  Name,  346  ;  Thickness 
of  Strata,  346 ;  Mode  of  Occurrence  of  Coal,  346 ;  Plication  and  Denudation, 

348  ;  Faults,  34,9  ;  Thickness  of  Seams,  349 ;  Number  and  Aggregate  Thickness, 

349  ;  Coal  Areas  of  the  United  States,  350 ;  Extra-Carboniferous  Coal,  351 ;  Coal- 
Areas  of  Different  Countries  compared,  351 ;  Relative  Production  of  Coal,  351. 
Origin  of  Coal  and  of  its  Varieties,  352 ;  Varieties  of  Coal,  353  ;  Varieties  de- 
pending upon  Purity,  353;  upon  Degree  of  Bituminization,  353;  upon  Propor- 
tion of  Fixed  and  Volatile  Matter,  353;  Origin  of  these  Varieties,  354;  Modes 
of  Decomposition — 1.  In  Contact  with  Air,  355;  2.  Out  of  Contact  with  Air, 
355  ;  Metamorphic  Coal,  356.     Plants  of  the  Coal,  their  Structure  and  Affinities, 
358 ;  Where  found,  358  :  Principal  Orders,  358 ;  1.  Conifers,  358  ;  Affinities  of 
Carboniferous  Conifers,  361 ;  2.  Ferns,  362 ;  3.  Lepidodendrids,  365 ;  4.  Sigil- 
larids,  368 ;  5.  Calamites,  370 ;  Conclusions  as  to  the  Affinities  of  the  Last  Three 
Orders,  372.     Theory  of  the  Accumulation  of  Coal,  373 ;  Presence  of  Water, 
373 ;  Growth  in  situ,  373 ;  At  the  Mouths  of  Rivers,  374 ;  Application  of  the 
Theory  to  the  American  Coal-Fields  :  (a)  Appalachian  Coal-Field,  375  ;  (b)  West- 
ern Coal-Fields,  376 ;  Appalachian  Revolution,  377.     Estimate  of  Time,  377 :  1. 
From  Aggregate  Amount  of  Coal,  377 ;  2.  From  Amount  of  Sediment,  377.    Physi- 
cal Geography  and  Climate  of  the  Coal  Period,  378  ;  Physical  Geography,  378 ; 
Climate,  379  ;  Cause  of  this  Climate,  380.     Iron-Ore  of  the  Coal-Measures,  383  ; 
Mode  of  Occurrence,  383 ;  Kinds  of  Ore,  383  ;  Theory  of  the  Accumulation  of 
the  Iron-Ore  of  the  Coal-Measures,  384.    Bitumen,  Petroleum,  and  Natural  Gas, 
386 ;  Geological  Relations,  386 ;  Oil-Formations,  387 ;  Principal  Oil-Horizons  of 
the  United  States,  387 ;  Laws  of  Interior  Distribution,  387 ;  Kinds  of  Rocks 
which  bear  Petroleum,  388.     Origin  of  Petroleum  and  Bitumen,  389 ;  Theories 
of,  389  ;  Chemical  Theory,  389  ;  Organic  Theory,  389 ;  Origin  of  Varieties,  390 ; 


CONTENTS.  XV 

PAGE 

Future  of  this  Industry  in  the  Eastern  United  States,  390.  Fauna  of  the  Car- 
boniffrous  Age,  390 ;  Invertebrates,  391 ;  Insects,  397  ;  Vertebrates  (Fishes),  398  ; 
Reptiles — Amphibians,  400:  1.  Reptilian  Footprints,  400;  2.  Dendrerpeton, 
401  ;  3.  Archegosaurus,  402 ;  4.  Eosaurus,  403  ;  Some  General  Observations  on 
the  Earliest  Reptiles,  404.  Some  General  Observations  on  the  whole  Palaeozoic^ 
405 ;  Physical  Changes,  405 ;  Chemical  Changes,  405  ;  Progressive  Change  in 
Organisms,  406 :  General  Comparison  of  the  Fauna  of  Palaeozoic  with  that  of 
Neozoic  Times,  407.  General  Picture  of  Palicozoic  Times,  407  ;  Transition  from 
the  Palaeozoic  to  the  Mesozoic — Permian  Period,  409  ;  The  Permian  a  Transition 
Period,  409 ;  Area  in  the  United  States,  413 ;  General  Character  of  Permian 
Organisms,  413. 

CHAPTER   IV. 

MESOZOIC  ERA.— AGE  OF  REPTILES 414-497 

General  Characteristics,  414;  Subdivisions,  414. 

SECTION  1.  TRIASSIO  PERIOD,  415  ;  Subdivisions,  515 ;  Flora,  416;  Animals,  416; 
Fishes,  416;  Reptiles,  417;  Affinities  of  Triassic  Reptiles,  419;  Birds,  421; 
Mammals,  421.  Origin  of  Rock-Salt,  421  ;  Age  of  Rock-Salt,  421 ;  Mode  of  Oc- 
currence, 422;  Theory  of  Accumulation,  422. 

SECTION  2.  JI;RASSIC  PERIOD,  424  ;  Origin  of  Oolitic  Limestone,  424  ;  Jurassic  Coal- 
Measures,  425  ;  Dirt-Beds — Fossil  Forest-Grounds,  425.  Plants,  426;  Animals^ 
428  ;  Corals,  428  ;  Brachiopods,  428  ;  Lamellibranchs,  428  ;  Cephalopods,  428  ; 
Ammonites,  430 ;  Belemnites,  432  ;  Crustacea,  434  ;  Insects,  435  ;  Fishes,  436  ; 
Reptiles,  437 ;  Birds,  444  ;  Origin  of  Birds,  448 ;  Mammals,  448 ;  Affinities  of 
the  First  Mammals,  448 ;  Origin  of  Mammals,  449. 

SECTION  8.  JCRA-TRIAS  IN  AMERICA,  450;  Distribution  of  Strata,  451.  Life-System, 
452  ;  Connecticut  River  Valley  Sandstone — The  Strata,  452  ;  Reptilian  Tracks, 
4.54  ;  Supposed  Bird-Tracks,  454  ;  Richmond  and  North  Carolina  Coal-Ficlds,456 ; 
Other  Patches,  458  ;  Interior  Plains  and  Pacific  Slope,  458  ;  Recent  Discoveries, 
460 ;  Atlantosaur  Bods,  460 ;  Dinosaurs,  460  ;  Ichthyosaurs,  466  ;  Birds,  466 ; 
Mammals,  467  ;  Physical  Geography  of  the  American  Continent  during  the  Jura- 
Trias  Period,  467 ;  Disturbances  which  closed  the  Period,  468. 

SECTION  4.  CRETACEOUS  PERIOD,  469  ;  Rock-System — Area  in  America,  469 ;  Physi- 
cal Geography,  469  ;  Rocks,  470 ;  Chalk,  470 ;  Origin  of  Chalk,  472  ;  Extent  of 
Chalk  Seas  of  Cretaceous  Times  in  Europe,  473  ;  Subdivisions  of  the  Cretaceous, 
474.  Life-System :  Plants,  474  ;  Origin  of  Dicoty Is,  477  ;  Potomac  Group,  477. 
Animals,  477 ;  Protozoa,  477  ;  Echinoderms,  478  ;  Mollusks,  478  ;  Vertebrates 
—Fishes,  482 ;  Reptiles,  484 ;  Birds,  488 ;  Mammals,  492.  Continuity  cf  the 
Chalk,  492;  General  Observations  on.  the  Mesozoic,  494;  Disturbance  which 
closed  the  Mesozoic,  494  ;  Transition  Period — Laramie,  495  ;  How  formed,  496  ; 
Plants  of,  497  ;  Coal  of,  498 ;  Animals,  498 ;  Reptiles,  499  ;  Mammals,  500. 

CHAPTER   V. 

CENOZOIC  ERA. — AGE  OF  MAMMALS 497-586 

General  Characteristics  of  the  Cenozoic  Era,  501 ;  Divisions,  501. 
SECTION    1.  TERTIARY   PERIOD. — Subdivisions,    502 ;    Rock-System — Area   in   the 
United  States,  503 :  Physical  Geography,  504 ;  Character  of  the  Rocks,  506 ; 
Coal,  506  ;  Life- System,  506 ;  General   Remarks,  506  ;    Plants,  507  ;  Diatoms, 
510;  Origin  of  Infusorial  Earths,  511;  Animals,  511  ;  Nummulitic  Limestone,      , 
512;  Insects,  514;  Fishes,  518;  Reptiles,  519;  Birds,  520;  Mammals— General 


Vi  CONTENTS. 

PAGE 

Remarks,  522;  1.  Eocene  Basin  of  Paris,  523;  2.  Siwalik  Hills,  India— Mio- 
cene, 524  ;  American  Localities:  3.  Marine  Eocene  of  Alabama,  528;  P.uerco 
Beds,  Lowest  Eocene,  529  ;  4.  Green  River  Basin — Wahsatch  Beds,  Lower  Eo- 
cene, 530  ;  5.  Green  River  Basin — Bridger  Beds — Middle  Eocene,  532  ;  6.  Mau- 
vaiscs  Torres  of  Nebraska — White  River  Basin — Miocene,  535  ;  Extreme  Differ- 
entiation of  Early  Tertiary  of  America  ;  7.  Mauvaises  Torres — Niobrara  Basin 
— Pliocene,  Similarity  of  the  Pliocene  Fauna  to  that  of  Europe,  537 ;  Some  Gen- 
eral Observations  on  the  Tertiary  Mammalian  Fauna,  537  ;  Size  of  Brain,  538  ; 
Genesis  of  Existing  Orders — Families,  Genera,  539 ;  Genesis  of  the  Horse,  540. 
General  Observations  on  the  Tertiary  Period,  543 ;  Changes  during  and  closing 
the  Period,  544. 

SECTION  2.  QUATERNARY  PERIOD,  545 ;  General  Characteristics,  545  ;  Subdivisions, 
545  ;  Special  Characteristics  of  these,  545.  Quaternary  Period  in  Eastern 
North  America.  I.  Glacial  Epoch.  The  Materials — Drift,  546  ;  The  Bowlders, 
548  ;  Surface-Rock  underlying  Drift,  549  ;  Extent,  550  ;  Marine  Deposits,  550. 
Theory  of  the  Origin  of  the  Drift,  551  ;  Statement  of  the  Most  Probable  View, 
551  ;  Objections  answei^ed,  551 ;  Probable  Condition  during  Glacial  Times  in 
America,  552  ;  Evidence  of  Elevation,  552  ;  Boundary  of  the  Ice-Sheet,  553  ; 
Second  Moraine,  553.  II.  Champlain  Epoch,  555  ;  Evidences  of  Subsidence, 
555  ;  Sea-Margins,  555  ;  Flooded  Lakes,  556  ;  Lake  Agassiz,  556  ;  Origin  of  the 
Loess,  559.  III.  Terrace  Epoch,  560  ;  Evidences— Sea,  560  ;  Lakes^_560 ;  Hist- 
ory of  the  Great  Lakes,  560;  Rivers,  561  ;  History  of  the  Mississippi  River,  561. 
Quaternary  Period  on  the  Western  Side  of  the  Continent,  562  ;  Sea-Submarine 
Channels,  562  ;  Glaciers,  563  ;  Flooded  Lakes,  566  ;  River-Beds,  567.  The  Qua- 
ternary in  Europe,  569.  1.  Epoch  of  Elevation — First  Glacial  Epoch,  570.  2. 
Epoch  of  Submergence — Champlain,  572.  3.  Epoch  of  Re-elevation — Second 
Glacial  Epoch — Terrace  Epoch,  573.  Southern  Hemisphere,'  573.  Some  General 
Remits  of  Glacial  Erosion.  1.  Fiords,  573  ;  2.  Glacial  Lakes,  574  ;  Different 
Kinds,  575.  Life  of  the  Quaternary  Period,  575  ;  Plants  and  Invertebrates,  575*; 
Mammals,  575  :  1.  Bone-Caverns,  577  ;  Origin  of  Cave  Bone-Rubbish,  578 ;  Origin 
of  Bone-Caverns,  578 ;  2.  Beaches  and  Terraces,  579  ;  3.  Marshes  and  Bogs,  580; 
4.  Frozen  Soils  and  Ice  Cliffs,  680 ;  Quaternary  Mammalian  Fauna  of  England, 
581 ;  Mammalian  Fauna  in  North  America,  581  ;  Bone-Caves,  582  ;  Marshes 
and  Bogs,  582  ;  River-Gravels,  584 ;  Quaternary  in  South  America,  584 ;  Aus- 
tralia, 588  ;  Geographical  Fauna  of  Quaternary  Times,  588.  Some  General  Ob- 
servations on  the  Whole  Quaternary,  589 ;  Cause  of  the  Climate,  589  ;  Effect  of 
Crust-Movements,  589 ;  Croll's  Theory,  590 ;  Wallace's  Views,  592  ;  Time  in- 
volved in  the  Quaternary  Period,  593 ;  The  Quaternary  a  Period  of  Revolution, 
— a  Transition  between  the  Cenozoic  and  the  Modern  Eras,  594 ;  Migration  of 
Species,  595  ;  General  Process  of  Evolution,  597 ;  Application  to  Australia,  598  ; 
Africa,  598 ;  Madagascar,  599 ;  British  Islands,  599  ;  Coast  Islands  of  California, 
699 ;  Drift  in  Relation  to  Gold,  600 ;  Age  of  the  River-Gravels,  602. 


CHAPTER  VI. 

PSYCHOZOIC  ERA.— AGE  OF  MAN. — RECENT  EPOCH  ....     603-619 
Characteristics,  603;  Distinctness  of  this  Era,  603  ;  The  Change  still  in  Progress 

— Examples  of  Recently  Extinct  Species,  605. 

I.  ANTIQUITY  OF  MAN,  607.  Primeval  Man  in  Europe,  608  ;  Supposed  Tertiary 
Man — Evidence  unreliable,  608  ;  Quaternary  Man — Mammoth  Age,  609 :  (a)  In 
River-Gravels,  609  ;  (b)  Bone-Caves — Engis  Skull,  609  ;  Neanderthal  Man,  610 ; 


CONTENTS.  xvii 

PAGE 

Men  of  Spy,  610  ;  Mentone  Skeleton,  610  ;  Reindeer  Age  or  Later  Palaeolithic, 
611  ;  Aurignac  Cave,  611  ;  Perigord  Caves,  612;  Conclusions,  613.  Neolithic 
Man;  Refuse-Heaps ;  Shell- Mounds ;  Kitchen- Middens,  613;  Transition  to  the 
Bronze  Age — Lake-Dwellings,  613.  Primeval  Man  in  America,  614  ;  Supposed 
Pliocene  Man,  Calaveras  Skull,  614;  Carson  Footprints,  615;  Quaternary  Man 
in  New  Jersey — in  Minnesota — in  Ohio,  616 ;  Quaternary  Man  in  Other  Coun- 
tries, 617  ;  Time  since  Man  appeared,  618. 
II.  CHARACTER  OF  PRIMEVAL  MAN,  619. 


TJ1TIVBRSIT7 


HSTTKODUCTORY. 


OF  GEOLOGY,   AND    OF  ITS  DEPARTMENTS. 

GEOLOGY  is  the  physical  history  of  the  earth  and  its  inhabitants, 
as  recorded  in  its  structure.  It  includes  an  account  of  the  changes 
through  which  they  have  passed,  the  laws  of  these  changes,  and  their 
causes.  In  a  word,  it  is  the  history  of  the  evolution  of  the  earth  and 
its  inhabitants.  ) 

The  fundamental  idea  of  geology,  as  well  as  its  principal  sub- 
divisions and  its  objects,  may  be  most  clearly  brought  out  by  compar- 
ing it  with  organic  science.  We  may  study  an  organism  from  three 
distinct  points  of  view :  1.  We  may  study  its  general  form,  the  parts 
of  which  it  is  composed,  and  its  minute  internal  structure.  This  is 
anatomy.  It  is  best  studied  in  the  dead  body.  2.  We  may  study  the 
living  body  in  action,  the  function  of  each  organ,  the  circulation  of  the 
fluids,  and  the  manner  in  which  all  contribute  to  the  complex  phenom- 
ena of  life.  This  is  physiology.  3.  We  may  study  the  living  and 
growing  body,  by  watching  the  process  of  development  from  the  egg 
to  the  adult  state,  and  striving  to  determine  its  laws.  This  is  embry- 
ology. 

So,  looking  upon  the  earth  as  an  organic  unit,  we  may  study  its 
form,  the  rocks  and  minerals  of  which  it  is  composed,  and  the  manner 
in  which  these  are  arranged ;  in  other  words,  its  external  form  and  in- 
ternal structure.  This  is  the  anatomy  of  the  earth,  and  is  called  struct- 
ural geology.  Or,  we  may  study  the  earth  under  the  action  of  physical 
and  chemical  forces,  the  action  and  reaction  of  land  and  water,  of  earth 
and  air,  and  the  effects  of  these  upon  the  form  and  structure.  This  is 
the  physiology  of  the  earth,  and  is  called  dynamical  geology.  Finally, 
we  may  study  the  earth  in  the  progress  of  its  development,  from  the 
earliest  chaotic  condition  to  its  present  condition  as  the  abode  of  man, 
and  attempt  to  determine  the  laws  of  this  development.  This  is  the 
embryology  of  the  earth,  or  historical  geology. 

Principal  Departments. — The  science  of  geology,  therefore,  nat- 
urally divides  itself  into  threa  parts,  viz. :  1.  Structural  geology,  or 
1 


2  INTRODUCTORY. 

geognosy.  2.  Dynamical  geology,  or  physical  and  chemical  geology. 
3.  Historical  geology,  or  the  history  of  the  earth. 

But  there  are  two  important  points  of  difference  between  geology 
and  organic  science.  The  central  department  of  organic  science  is 
physiology,  and  both  anatomy  and  embryology  are  chiefly  studied  to 
throw  light  on  this.  But  the  central  department  of  geology,  to  which 
the  others  are  subservient,  is  history.  Again :  in  case  of  organisms 
— especially  animal  organisms — the  nature  of  the  changes  producing 
development  is  such  that  the  record  of  each  previous  condition  is  suc- 
cessively and  entirely  obliterated ;  so  that  the  science  of  embryology  is 
possible  only  by  direct  observation  of  each  successive  stage.  If  this 
were  true  also  of  the  earth,  a  history  of  the  earth  would,  of  course,  be 
impossible.  But,  fortunately,  we  find  that  each  previous  condition  of 
the  earth  has  left  its  record  indelibly  impressed  on  its  structure. 

Order  of  Treatment. — The  prime  object  of  geology  is  to  determine 
the  history  of  the  earth,  and  of  the  organisms  which  have  successively 
inhabited  its  surface.  The  structure  and  constitution  of  the  earth  are 
the  materials  of  this  history,  and  the  physical  and  chemical  changes 
now  going  on  'around  us  are  the  means  of  interpreting  this  structure 
and  constitution.  Evidently,  therefore,  the  only  logical  order  of  pre- 
senting the  facts  of  geology  is  to  study,  first,  the  causes,  physical  and 
chemical,  now  in  operation  and  producing  structure ;  then  the  structure 
and  constitution  of  the  earth  which,  from  the  beginning,  have  been 
produced  by  similar  causes ;  and,  lastly,  from  the  two  preceding  to  un- 
fold the  history  of  the  earth. 

Geology  may  be  defined,  therefore,  as  the  history  of  the  earth  and 
its  inhabitants,  as  revealed  in  its  structure,  and  as  interpreted  by 
causes  still  in  operation. 

There  is  no  other  science  which  requires  for  its  full  comprehension 
a  general  knowledge  of  so  many  other  departments  of  science.  A 
knowledge  of  mathematics,  physics,  and  chemistry,  is  required  to  under- 
stand dynamical  geology ;  a  knowledge  of  mineralogy  and  lithology  is 
required  to  understand  structural  geology ;  and  a  knowledge  of  zoology 
and  botany  is  required  to  understand  the  affinities  of  the  animals  and 
plants  which  have  successively  inhabited  the  earth,  and  the  laws  which 
have  controlled  their  distribution  in  time. 


PART  I. 
DYNAMICAL  GEOLOGY. 


THE  agencies  now  in  operation,  modifying  the  structure  of  the  sur- 
face of  the  earth,  may  be  classed  under  four  heads,  viz.,  atmospheric 
agencies,  aqueous  agencies,  igneous  agencies,  and  organic  agencies. 
These  agencies  have  operated  from  the  beginning,  and  are  still  in 
operation.  We  study  their  operation  now,  in  order  that  we  may  un- 
derstand their  effects  in  previous  epochs  of  the  earth's  history — i.  e., 
the  structure  of  the  earth. 

While  all  geologists  agree  that  the  nature  of  the  agencies  which 
have  operated  in  modifying  the  earth's  surface  has  remained  the  same 
from  the  beginning,  they  differ  in  their  views  as  to  the  energy  of  their 
operation  in  different  periods.  Some  believe  that  their  energy  has  been 
much  the  same  throughout  the  whole  history  of  the  earth,  while  others 
believe  that  many  facts  in  the  structure  of  the  earth  require  much 
greater  operative  energy  than  now  exists.  We  will  attempt  to  show 
hereafter  that  neither  of  these  extreme  opinions  is  probably  true,  but 
that  some  of  these  agencies  have  been  decreasing,  while  others  have 
been  increasing,  with  the  progress  of  time.  It  is  the  constant  change 
of  balance  between  these  which  determines  the  development  of  the 
earth. 


CHAPTER  T. 

A  TMOSPHERIC  A  GENCIES. 

THE  general  effect  of  atmospheric  agencies  is  the  disintegration  of 
rocks  and  the  formation  of  soils.  The  atmosphere  is  composed  of  nitro- 
gen and  oxygen,  with  small  quantities  of  watery  vapor  and  of  carbonic 
acid.  There  are  but  few  rocks  which  are  not  gradually  disintegrated 
under  the  constant  chemical  action  of  the  atmosphere.  The  chemical 
agents  of  these  changes  are  oxygen,  carbonic  acid,  and  watery  vapor, 
the  nitrogen  being  inert.  To  these  must  be  added,  where  vegetation 


4:  ATMOSPHERIC   AGENCIES. 

is  present,  the  products  of  vegetable  decomposition,  especially  ammo- 
nia and  humus  acids* 

Atmospheric  agencies  graduate  so  insensibly  into  aqueous  agencies 
that  it  is  difficult  to  define  their  limits.  Water,  holding  in  solution 
carbonic  acid  and  oxygen,  may  exist  as  invisible  vapor ;  or,  partially 
condensed  as  fogs ;  or,  completely  condensed,  as  rain  falling  upon  and 
percolating  the  earth.  In  all  these  forms  its  chemical  action  is  the 
same,  and,  therefore,  can  not  be  separated  and  treated  under  different 
classes ;  and  yet  the  same  rain  runs  off  from  and  erodes  the  surface  of 
the  earth,  comes  out  from  the  strata  and  forms  springs,  rivers,  etc.,  all 
of  which  naturally  fall  under  aqueous  agencies.  We  shall,  therefore, 
treat  of  the  chemical  effects  of  atmospheric  water  in  the  disintegration 
of  rocks,  and  the  formation  of  soils,  under  the  head  of  atmospheric 
agencies  ;  and  the  mechanical  effects  of  the  same,  in  eroding  the  surface 
and  carrying  away  the  soil  thus  formed,  under  the  head  of  aqueous 
agencies.  In  moist  climates  vegetation  clothes  and  protects  soil  from 
erosion,  but  favors  decomposition  of  rocks  and  formation  of  soil. 

Atmospheric  agencies  are  obscure  in  their  operation,  and,  therefore, 
imperfectly  understood.  Yet  these  are  not  less  important  than  aqueous 
agencies,  since  they  are  the  necessary  condition  of  the  operation  of  the 
latter.  Unless  rocks  were  first  disintegrated  into  soils  by  the  action 
of  the  atmosphere,  they  would  not  be  carried  away  and  deposited  as 
sediments  by  the  agency  of  water.  These  two  agencies  are,  therefore, 
of  equal  power  and  importance  in  geology,  but  they  differ  very  much  in 
the  conspicuousness  of  their  effects.  *  Atmospheric  agencies  act  almost 
equally  at  all  times  and  at  all  places,  and  their  effects,  at  any  one  place 
or  time,  are  almost  imperceptible.  Aqueous  agencies,  on  the  contra- 
ry, in  their  operation  are  occasional,  and  to  a  great  extent  local,  and 
their  effects  are,  therefore,  more  striking  and  easily  studied.  Never- 
theless, the  aggregate  effects  of  the  former  are  equal  to  those  of  the 
latter. 

Soils. — All  soils  (with  the  trifling  exception  of  the  thin  stratum 
of  vegetable  mold  which  covers  the  ground  in  certain  localities)  are 
formed  from  the  disintegration  of  rocks.  Sometimes  the  soil  is  formed 
in  situ,  and,  therefore,  rests  on  its  parent  rock.  Sometimes  it  is  re- 
moved as  fast  as  formed,  and  deposited  at  a  distance  more  or  less  remote 
from  the  parent  rock.  The  evidence  of  this  origin  of  soils  is  clearest 
when  the  soil  is  formed  in  situ.  In  such  cases  it  is  often  easy  to  trace 
every  stage  of  gradation  between  perfect  rock  and  perfect  soil.  This 
is  well  seen  in  railroad  cuttings,  and  in  wells  in  the  gneissic  or  so-called 
primary  region  of  our  southern  Atlantic  slope.  On  examining  such  a 

*  Alexis  Julien,  Proceedings  of  the  American  Association  for  the  Advancement  of 
Science,  vol.  xxviii,  p.  311  ct  scq. 


ATMOSPHERIC  AGENCIES.  5 

section,  we  find  near  the  surface  perfect  soil,  generally  red  clay ;  beneath 
this  we  find  the  same  material,  but  lighter  colored,  coarser,  and  more 
distinctly  stratified ;  beneath  this,  but  shading  into  it  by  imperceptible 
gradations,  we  have  what  seems  to  be  stratified  rock,  but  it  crumbles 
into  co'arse  dust  in  the  hand ;  this  passes  by  imperceptible  gradations 
into  rotten  rock,  and  finally  into  perfect  rock.  There  can  be  no  doubt 
that  these  are  all  different  stages  of  a  gradual  decomposition.  But 
closer  observation  will  make  the  proof  still  clearer.  In  gneissic  and 
other  metamorphic  regions  it  is  not  uncommon  to  find  the  rock  trav- 
ersed, in  various  directions,  by  veins  of  quartz  or  flint.  Now,  in  sec- 
tions such  as  those  mentioned  above,  it  is  common  to  find  such  a  quartz- 
vein  running  through  the  rock  and  upward  through  the  superincumbent 
soil,  until  it  emerges  on  the  surface.  In  the  slow  decomposition  of  the 
rock  into  soil,  the  quartz-vein  has  remained  unchanged,  because  quartz 
is  not  affected  by  atmospheric  agencies.  Chemical  analysis,  also,  always 
shows  an  evident  relation  between  the  soil  and  the  subjacent  or  country 
rock,  except  in  cases  in  which  the  soil  has  been  brought  from  a  consid- 
erable distance. 

The  depth  to  which  soil  will  thus  accumulate  depends  partly  on  the 
nature  of  the  rock  and  the  rapidity  of  decomposition,  partly  on  the  slope 
of  the  ground,  and  partly  on 
climate.  In  Brazil,  undis- 
turbed soils  are  found  three 
hundred  feet  deep.*  When 
the  slope  is  considerable,  as 
at  d  (Fig.  1),  the  rocks  are 
Jhare,  not  because  no  soil  is 
formed,  but  because  it  is  re- 

FIG.  1.— Ideal  Section,  showing  Rock  passing  into  Soil. 

moved   as  fast  as  formed; 

while  at  a  the  soil  is  deep,  being  formed  partly  by  decomposition  of 
rock  in  situ,  and  partly  of  soil  brought  down  from  d.  Wherever  per- 
fect soil  is  found  resting  on  sound  rock,  the  soil  has  been  shifted. 

If  rocks  were  solid  and  impervious  to  water,  this  process  would  be 
almost  inconceivably  slow ;  but  we  find  that  all  rocks,  for  reasons  to  be 
discussed  hereafter,  are  broken  by  fissures  into  irregular  prismatic 
blocks,  so  that  a  perpendicular  cliff  of  rock  usually  presents  the  appear- 
ance of  rude  gigantic  masonry.  These  fissures,  or  joints,  increase  im- 
mensely the  surface  exposed  to  the  action  of  atmospheric  water.  Again, 
on  closer  inspection,  we  find  even  the  most  solid  parts  of  rocks,  i.  e.,  the 
blocks  themselves,  penetrated  with  capillary  fissures  which  allow  water 
to  reach  every  part.  Thus  the  rock  is  decomposed,  or  becomes  rotten, 
to  a  great  depth  below  the  surface.  But,  while  the  rock  is  gradually 

*  American  Journal  of  Science,  1884,  vol.  xxvii,  p.  130. 


ATMOSPHERIC  AGENCIES. 


FIG.  3.—^,  vegetal  soil;  6,  mineral  soil;  c.  harder 
portions  of  rock  left  in  process  of  disintegra- 
tion; d,  underlying  rock. 


FIG.  2. 

changed  into  soil,  the  soil  is  also  slowly  carried  away  by  agencies  to  be 
hereafter  considered ;  and  these  changes,  taking  place  more  rapidly  in 
some  places  than  in  others,  give  rise  to  a  great  variety  of  forms,  some 
of  which  are  represented  in  the  accompanying  figure  (Fig.  2). 

In  the  process  of  disintegra- 
tion the  original  blocks  lose  their 
prismatic  form,  and  become  more 
or  less  rounded,  and  are  then  called 
^Dividers  of  disintegration.  These 
may  lie  on  the  surface  (Fig.  2),  or 
may  be  buried  in  the  soil  (Fig.  3). 
When  of  great  size  and  very  solid, 
so  as  to  resist  decomposition  to  a  greater  extent  than  the  surrounding 
rocks,  they  often  form  huge 
rocking-stones  (Fig.  4).  These 
must  not  be  confounded  with 
true  bowlders  and  rocking- 
stones  which  are  brought  from 
a  distance,  by  agencies  which 
we  will  discuss  hereafter,  and 
which  are,  therefore,  entirely  different  from  the  subjacent  or  coun- 
try rock. 

General  Explanation. — The  process  of  rock-disintegration  may  be 
explained,  in  a  general  way,  as  follows :  Almost  all  rocks  are  composed 
partly  of  insoluble  materials,  and  partly  of  materials  which  are  slowly 
dissolved  by  atmospheric  water.  In  the  process  of  time,  therefore, 
these  latter  are  dissolved  out,  and  the  rock  crumbles  into  an  insoluble 
dust,  more  or  less  saturated  with  water  holding  in  solution  the  soluble 
ingredients.  To  illustrate :  common  hardened  mortar  may  be  regarded 
as  artificial  stone ;  it  consists  of  carbonate  of  lime  and  sand ;  the  car- 
bonate of  lime  is  soluble  in  water  containing  carbonic  acid  (atmospheric 
water),  while  the  sand  is  quite  insoluble.  If,  therefore,  such  mortar  be 
exposed  to  the  air,  it  eventually  crumbles  into  _sand,  moistened  with 
water  containing  lime  in  solution.  Again,  to  take  a  case  which  often 
occurs  in  Nature,  it  is  not  uncommon  to  find  rock  through  which  iron 
pyrites,  FeSa,  is  abundantly  disseminated.  This  mineral  is  insoluble ; 
but  under  the  influence  of  water  containing  oxygen  (atmospheric  water) 
it  is  slowly  oxidized  and  changed  into  sulphate  of  iron,  or  copperas, 
which,  being  soluble,  is  washed  out,  and  the  rock  crumbles  into  an 


FIG.  4. 


ATMOSPHERIC   AGEXCIES.  7 

insoluble  dust  or  soil,  saturated  with  a  solution  of  the  iron  salt.  We 
have  given  these  only  as  illustrative  examples.  We  now  proceed  to 
give  examples  of  the  principal  kinds  of  rocks,  and  of  the  soils  formed 
by  their  disintegration. 

Granite,  Gneiss,  Volcanic  Rocks,  etc. — Granite  and  gneiss  are  mainly 
composed  of  three  minerals,  quartz,  feldspar,  and  mica,  aggregated  to- 
gether into  a  coherent  mass.  Quartz  is  unchangeable  and  insoluble  in 
atmospheric  water.  Mica  is  also  very  slowly  affected.  Feldspar  is, 
therefore,  the  decomposable  ingredient.  But  feldspar  is,  itself,  a  com- 
plex substance,  partly  soluble  and  partly  insoluble.  It  is  essentially  a 
silicate  of  alumina,  united  with  a  silicate  of  potash  or  soda,  although  it 
often  contains  also  small  quantities  of  iron  and  lime.  Now,  while  the 
silicate  of  alumina  is  perfectly  insoluble,  the  other  silicates  are  slowly 
dissolved  by  atmospheric  water,  with  the  formation  of  carbonates,  and 
the  silicate  of  alumina  is  left  as  kaolin  or  clay.  But,  since  we  may 
regard  the  original  rock  as  made  up  of  quartz  and  mica,  bound  together 
by  a  cement  of  feldspar,  the  disintegration  of  the  latter  causes  the  whole 
rock  to  lose  its  coherence,  and  the  final  result  of  the  process  is  a  mass 
of  clay  containing  grains  of  sand  and  scales  of  mica,  and  moistened 
with  water  containing  a  potash  salt.  If  there  be  any  iron  in  the  feld- 
spar, or  if  there  be  other  decomposable  ingredients  in  the  rock  contain- 
ing iron,  such,  for  example,  as  hornblende,  the  clay  will  be  red.  This 
is  precisely  the  nature  of  the  soil  in  all  our  primary  regions.  Volcanic 
rocks  decompose  into  clay-soils  often,  though  not  always,  deeply  colored 
with  iron. 

Limestone. — Pure  limestone  may  be  regarded  as  composed  of  gran- 
ules of  carbonate  of  lime,  cohering  by  a  cement  of  the  same.  The  dis- 
solving of  the  cement  by  atmospheric  water  forms  a  lime-soil,  moistened 
with  a  solution  of  carbonate  of  lime  (hard  water).  Impure  limestone 
is  a  carbonate  of  lime,  more  or  less  mixed  with  sand  or  clay ;  by  disin- 
tegration it  forms,  therefore,  a  marly  soil. 

Sandstones. — Sandstones  consist  of  grains  of  sand  cemented  together 
by  carbonate  of  lime  or  peroxide  of  iron.  Where  peroxide  of  iron  is 
the  cementing  substance,  the  rock  is  almost  indestructible,  since  this 
substance  is  not  changed  by  atmospheric  water :  hence  the  great  value 
of  red  sandstone  as  a  building-material.  But,  when  carbonate  of  lime 
is  the  cementing  material,  this  substance,  being  soluble  in  atmospheric 
water,  is  easily  washed  out,  and  the  rock  rapidly  disintegrates  into  a 
sandy  soil. 

Slate. — In  a  similar  manner  slate-rocks  disintegrate  into  a  pure  clay 
soil  by  the  solution  of  their  cementing  material,  which  is  often  a  small 
quantity  of  carbonate  of  lime. 

There  can  be  no  doubt  that  all  soils  are  formed  in  the  manner  above 
indicated.  We  have  given  examples  of  soils  formed  in  situ,  but,  as 


8 


ATMOSPHERIC   AGENCIES. 


soils  are  often  shifted,  they  are  usually  composed  of  a  mixture  formed 
by  the  disintegration  of  several  kinds  of  rock.  In  some  cases  the  soil 
has  been  formed  in  situ  during  the  present  geological  epoch,  and  the 
process  is  still  going  on  before  our  eyes.  Such  are  the  soils  of  the  hills 
of  the  up-country  or  primary  region  of  our  Southern  Atlantic  States.* 
Sometimes  the  soil  formed  in  the  same  way  has  been  shifted  to  a  greater 
or  less  distance.  Such  are  the  soils  of  our  valleys  and  river-bottoms. 
In  still  other  cases  the  soil  has  been  formed  by  the  process  already  de- 
scribed, and  transported  during  some  previous  geological  epoch  and  not 
reconsolidated.  Such  are  many  of  the  soils  of  the  Southern  low-country 
or  tertiary  region. 

MECHANICAL  AGENCIES  OF  THE  ATMOSPHERE. 
Frost. — Water,  penetrating  rocks  and  freezing,  breaks  off  huge  frag- 
ments :  these  by  a  similar  process  are  again  broken  and  rebroken  until 
the  rock  is  reduced  to  dust.  These  effects  are  most  conspicuous  in  cold 
climates  and  in  mountain-regions.  In  cold  climates  huge  piles  of 
bowlders  and  earth  are  always  seen  at  the  base  of  steep  cliffs  (Fig.  5). 

Such  a  pile  of  materials,  the  ruins 
of  the  cliff  above,  is  called  a  talus. 
In  mountainous  regions  frost  is  a 
powerful  agent  in  disintegrating  the 
rocks,  and  in  determining  the  out- 
lines of  mountain-peaks.  This  is 
well  seen  in  the  Alps  and  in  the 
Sierra. 

Winds. — The  effect  of  winds  is 
seen  in  the  phenomenon  of  shifting 
sands.  At  Cape  Cod,  for  instance, 
the  sands  thrown  ashore  by  the  sea  are  driven  by  the  winds  inland,  and 
thus  advance  upon  the  cultivated  lands,  burying  them  and  destroying 
their  fertility.  The  sands  from  the  beach  on  the  Pacific  coast  near 
San  Francisco  are  driven  inland  in  a  similar  manner,  and  are  now  reg- 
ularly encroaching  upon  the  better  soil.  Large  areas  of  the  fertile 
alluvial  soil  of  Egypt,  together  with  their  cities  and  monuments,  have 
been  buried  by  the  encroachments  of  the  Sahara  Desert.  The  same 
phenomena  are  observed  on  various  parts  of  the  coast  of  France,  Hol- 
land, and  England.  The  rate  of  advance  has  been  measured  in  some 
instances.  Thus  on  the  coast  of  Suffolk  it  is  said  to  advance  at  the 
rate  of  about  five  miles  a  century;  at  Cape  Finisterre,  according  to 
Ansted,  at  the  rate  of  thirty-two  miles  per  century,  or  five  hundred  and 
sixty  yards  per  annum.  The  Dunes  of  England  and  Scotland  are  such 


FIG.  5. 


In  the  Northern  States,  in  the  region  of  the  Drift,  nearly  all  the  soil  has  been  shifted. 


RIVERS.  9 

barrens  of  drifting  sand.  Hills  may  be  formed  in  this  manner  thirty 
to  forty  feet  in  height.  In  the  nearly  rainless  regions  of  the  interior 
of  our  continent,  high  winds,  laden  with  sand  and  gravel,  are  a  power- 
ful agent  in  sculpturing  the  rocks  into  the  fantastic  forms  so  often 
found  there  *  In  such  regions,  also,  extensive  deposits  of  wind-borne 
particles  are  sometimes  found.  This  is  especially  true  in  the  interior 
of  Asia  and  in  China,  where,  according  to  Richthofen,  such  deposits 
are  hundreds  of  feet  in  thickness  and  cover  thousands  of  square  miles. 
The  geological  importance  of  dust-depo,QUs  has  only  recently  been  ap- 
preciated. 


CHAPTER  II. 

AQUEOUS  AGENCIES. 

THE  agencies  of  water  are  either  mechanical  or  chemicaL  The 
mechanical  agencies  of  water  may  be  treated  under  the  threefold  aspect 
of  erosion,  transportation,  and  sedimentary  deposits.  We  will  consider 
them  under  the  heads  of  Rivers,  Oceans,  and  Ice.  Under  chemical 
agencies  we  will  consider  the  phenomena  of  chemical  deposits  in 
^Springs  and  Lakes. 

(  Rivers  .......  Erosion,  Transportation,  Deposit. 

Mechanical.  \  Ocean  .......         " 

(  Ice  ..........         "  "  " 

chemical.  DT8iti?- 


SECTION  1.  —RIVERS. 

Under  the  head  of  river  agencies  we  include  all  the  effects  of  circu- 
lating meteoric  water  from  the  time  it  falls  as  rain  until  it  reaches  the 
ocean  :  i.  e.,  all  the  effects  of  Rain  and  Rivers. 

Water,  in  the  form  of  vapor,  fogs,  or  rain,  percolating  through  the 
earth,  slowly  disintegrates  the  hardest  rocks.  Much  of  these  percolat- 
ing waters,  after  accomplishing  the  work  of  soil-making,  already  treated 
in  the  preceding  chapter,  reappears  on  the  surface  in  the  form  of  springs, 
and  gives  rise  to  streamlets.  A  large  portion  of  rain-water,  however, 
never  soaks  into  the  earth,  but  runs  off  the  surface,  forming  rills,  which 
by  erosion  produce  furrows.  The  uniting  rills  form  rivulets,  which 
excavate  gullies.  The  rivulets,  uniting  with  one  another  and  with  the 
streamlets  issuing  from  springs,  form  torrents,  which  in  their  course 
excavate  ravines,  gorges,  and  canons.  The  uniting  torrents,  finally  issu- 

*  Gilbert,  U.  S.  Geographical  Surveys—  Lieutenant  Wheeler  in  charge,  vol.  iii,  Geology, 
p.  82. 


10  AQUEOUS  AGENCIES. 

ing  from  their  mountain-home  upon  the  plains,  form  great  rivers,  which 
deposit  their  freight  partly  in  their  course  and  partly  in  the  sea.  Such 
is  a  condensed  history  of  rain-water  on  its  way  to  the  ocean  whence  it 
came.  Our  object  is  to  study  this  history  in  more  detail. 

Erosion  of  Rain  and  Rivers. 

The  whole  amount  of  water  falling  on  any  land-surface  may  be 
divided  into  three  parts:  1.  That  which  rushes  immediately  off  the 
surface,  and  causes  the  floods  of  the  rivers,  especially  the  smaller 
streams ;  2.  That  which  sinks  into  the  earth,  and,  after  doing  its 
chemical  work  of  soil-making,  reappears  as  springs,  and  forms  the 
regular  supply  of  streams  and  rivers ;  and,  3.  That  which  reaches  the 
sea  wholly  by  subterranean  channels.  Of  these,  the  first  two  are  the 
grand  erosive  agents,  and  these  only  concern  us  at  present.  Of  these, 
the  former  predominate  in  proportion  as  the  land-surface  is  bare;  the 
latter  in  proportion  as  it  is  covered  with  vegetation. 

Hydrographical  Basin. — An  hydrographical  basin  of  a  river,  lake, 
or  gulf,  is  the  whole  area  of  land  the  rainfall  of  which  drains  into  that 
river,  lake,  or  guJJL  Thus  the  hydrographical  basin  of  the  Mississippi 
River  is  the  whole  area  drained  by  that  river  It  is  bounded  on  the 
east  and  west  by  the  Alleghany  and  Rocky  Mountains,  and  on  the 
north  by  a  low  ridge  running  from  Lake  Superior  westward.  The 
whole  area  of  continents,  with  the  exception  of  rainless  deserts,  may  be 
regarded  as  made  up  of  hydrographical  basins.  The  ridge  which  sepa- 
rates contiguous  basins  is  called  a  water-shed.  It  is  evident  that  every 
portion  of  the  land,  with  the  exception  of  the  rainless  tracts  already 
mentioned,  is  subject  to  the  erosive  agency  of  water,  and  is  being  worn 
away  and  carried  into  the  sea.  There  have  been  various  attempts  to 
estimate  the  rate  of  this  general  erosion. 

Rate  of  Erosion  of  Continents. — This  is  usually  estimated  as  follows : 
Some  great  river,  such  as  the  Mississippi,  is  taken  as  the  subject  of 
experiment.  By  accurate  measurement  during  every  portion  of  the 
year,  the  average  amount  of  water  discharged  into  the  sea  per  second, 
per  hour,  per  day,  per  year,  is  determined.  This  is  a  matter  of  no 
small  difficulty,  as  it  involves  the  previous  determination  of  the  average 
cross-section  of  the  river  and  the  average  velocity  of  the  current.  The 
average  cross-section  X  average  velocity  =  the  average  discharge  per 
second :  from  which  may  be  easily  obtained  the  annual  discharge.  Next, 
by  experiment  during  every  month  of  the  year,  the  average  quantity  of 
mud  contained  in  a  given  quantity  of  water  is  also  determined.  By  an 
easy  calculation  this  gives  us  the  annual  discharge  of  mud,  or  the  whole 
quantity  of  insoluble  matter  removed  from  the  hydrographical  basin  in 
one  year.  This  amount,  divided  by  the  area  of  the  river-basin,  will  give 
the  average  thickness  of  the  layer  of  insoluble  matter  removed  from  the 


EROSIOX   OF  RAIN  AND   RIVERS.  H 

basin  in  one  year.  To  this  must  be  added  the  soluble  matters,  which 
are  about  one  sixth  as  much  as  the  insoluble. 

Estimates  of  this  kind  have  been  made  for  two  great  rivers,  viz.,  the 
Ganges  and  the  Mississippi.  The  whole  amount  of  sediment  annually 
carried  to  the  sea  by  thejjranges  has  been  estimated  as_Gj368,000,000 
cubic  feet.  This  amount,  spread  over  the  whole  basin  of  the  Ganges 
(400,000  square  miles),  would  make  a  layer  -p^j  of  a  foot  thick.  The 
Ganges,  therefore,  erodes  its  basin  one  foot  in  1,751  years.*  The  area 
of  the  Mississippi  basin  is  1,244,000  square  miles.  The  annual  dis- 
charge of  sediment,  according  to  the  recent  and  accurate  experiments 
of  Humphrey  and  Abbot,  is  7,471,411,200  cubic -feet,  a  mass  sufficient 
to  cover  an  area  of  one  square  mile,  268  feet  deep.f  This  spread  over 
the  whole  basin  would  cover  it  4g*4ff  of  a  foot.  Therefore,  this  river 
removes  from  its  basin  a  thickness  of  one  foot  in  4,640  years.  The 
cause  of  the  great  difference  in  favor  of  the  Ganges  is,  that  this  river 
is  situated  in  a  country  subject  to  very  great  annual  fall  of  water,  the 
whole  of  which  falls  during  a  rainy  season  of  six  months.  The  rains 
are  therefore  very  heavy,  and  the  floods  and  consequent  erosion  propor- 
tionately great.  The  erosive  power  of  this  river  is  still  further  increased 
by  the  great  slope  of  the  basin,  as  it  takes  its  rise  in  the  Himalaya,  the 
highest  mountains  in  the  world. 

Now,  since  continents  may  be  regarded  as  made  up  of  hydrographi- 
cal  basins,  the  average  rate  of  their  erosion  may  be  determined  either  by 
making  similar  experiments  on  all  the  rivers  of  the  world,  or,  since  this 
is  impracticable,  by  taking  some  river  as  an  average.  We  believe  the 
Mississippi  is  much  nearer  an  average  river  than  the  Ganges.  It  can 
hardly  be  less  than  the  average,  for  a  considerable  portion  of  the  earth 
— as  rainless  deserts — is  not  subject  to  any  erosion.  It  is  probable, 
therefore,  that  the  whole  surface  of  continents  is  eroded  at  a  rate  not 
exceeding  one  foot  in  4,640  years.  For  convenience  we  will  call  it  one 
foot  in  5,000  years.  We  will  use  this  estimate  when  we  come  to  speak 
of  the  actual  erosion  which  has  occurred  in  geological  times. 

Law  of  Variation  of  Erosive  Power. — The  erosive  power  of  water,  or 
its  power  of  overcoming  cohesion,  varies  as  the  square  of  the  velocity  of 
the  current  (p  oc  ya).  The  velocity  depends  upon  the  slope  of  the  bed, 
the  depth  of  the  water,  and  many  other  circumstances,  so  numerous  and 
complicated  that  it  has  been  found  impossible  to  reduce  it  to  any  simple 
law.  The  angle  of  slope,  however,  is  evidently  the  most  important  cir- 
cumstance which  controls  velocity,  and  therefore  erosive  power.  In  the 
upper  portions  of  great  rivers,  like  the  Mississippi,  the  erosion  is  very 
great ;  while  in  the  plains  near  the  mouth  there  may  be  no  erosion,  but, 

*  Philosophical  Magazine,  vol.  v,  p.  261. 

f  Humphrey  and  Abbot,  Report  on  Mississippi  River,  pp.  148-150. 


12  AQUEOUS  AGENCIES. 

on  the  contrary,  sedimentary  deposit.  The  high  lands,  therefore,  espe- 
cially mountain-chains,  are  the  great  theatres  of  erosion.  Pure  water, 
however,  erodes  very  slowly,  the  main  agents  of  erosion  being  the  gravel 
and  sand  carried  along  by  the  current.  The  general  effect  of  erosion  is 
leveling.  If  unopposed,  the  final  effect  would  be  to  cut  down  all  lands 
to  the  level  of  the  sea,  at  an  average  rate  of  about  one  foot  in  five  thou- 
sand years.  But  the  immediate  local  effect  is  to  increase  the  inequalities 
of  land-surface,  deepening  the  furrows,  gullies,  and  gorges,  and  increas- 
ing the  intervening  ridges  and  peaks.  The  effect,  therefore,  is  like 
that  of  a  graver's  tool,  constantly  cutting  at  every  elevation,  but  making 
trenches  at  every  stroke. 

Thus  land-surfaces  everywhere,  especially  in  mountain-regions,  are 
cut  away  by  a  process  of  sculpturing,  and  the  debris  carried  to  the  low- 
lands and  to  the  sea.  The  smaller  lines  and  more  delicate  touches  are 
due  to  rain,  the  deeper  trenches  or  heavier  chiselings  to  rivers  proper. 
The  effects  of  the  former  are  more  general  and  far  greater  in  the  aggre- 
gate, but  the  effects  of  the  latter  are  far  more  conspicuous.  It  is  only 
under  certain  conditions  that  rain-sculpture  becomes  conspicuous. 
These  conditions  seem  to  be  a  bare  soil  and  absence  of  frost.  Beautiful 
examples  are  found  in  the  arid  regions  of  southern  Utah. 

We  now  proceed  to  discuss  the  more  conspicuous  effects  of  water 
concentrated  in  river-channels. 

EXAMPLES  OF  GREAT  EROSION  NOW  GOING  ON  :  WATERFALLS. 

The  erosive  power  of  water  is  most  easily  studied  in  ravines,  gorges, 
canons,  and  especially  in  great  waterfalls.  One  of  the  most  interesting 
of  these  is  Niagara. 

Niagara  :  General  Description. — The  plateau  on  which  stands  Lake 
Erie  (P  N,  Fig.  6)  is  elevated  about  three  hundred  feet  above  that  of 


L.ERIE. 


Fia.  6.— Ideal  Longitudinal  Section  through  Niagara  River  from  Lake  Erie  to  Lake  Ontario. 

Lake  Ontario,  and  is  terminated  abruptly  by  an  escarpment  about  three 
hundred  feet  high  (P).  From  this  point  a  narrow  gorge  with  nearly 
perpendicular  sides,  and  two  hundred  to  three  hundred  feet  deep,  runs 
backward  through  the  higher  or  Erie  plateau  as  far  as  the  falls  (N). 
The  Niagara  River  runs  out  of  Lake  Erie  and  upon  the  Erie  plateau  as 
far  as  the  falls,  then  pitches  a  hundred  and  sixty-seven  feet  perpendicu- 
larly, and  then  runs  in  the  gorge  for  seven  miles  to  Queenstown  ($), 
where  it  emerges  on  the  Ontario  plateau.  Long  observation  has  proved 


WATERFALLS. 


13 


that  the  position  of  the  fall  is  not  stationary,  but  slowly  recedes  at  a 
rate  which  has  been  variously  estimated  from  one  to  three  feet  per  an- 
num. The  process  of  recession  has  been  carefully  observed,  and  the 
reason  why  it  maintains  its  perpendicularity  is  very  clear.  The  surface- 
rock  of  Erie  plateau  is  a  firm  limestone  (a).  Beneath  this  is  a  softer 
shale  (b).  This  softer  rock  is  rapidly  eroded  by  the  force  of  the  falling 
water,  and  leaves  the  harder  limestone  projecting  as  table-rocks.  From 
time  to  time  these  projecting  tables  are  loosened  and  fall  into  the  chasm 
below.  This  process  is  facilitated  by  the  joint  structure  spoken  of  on 
page  5. 

Recession  of  the  Falls. — Naw,  there  is  every  reason  to  believe  that 
the  fall  was  originally  situated  at  Queenstown,  the  river  falling  over 
the  escarpment  at  that  place,  and  that  it  has  worked  its  way  backward 
seven  miles  to  its  present  position  by  the  process  we  have  just  described. 
These  reasons  are  as  follows :  1.  The  general  configuration  of  the  country 
as  already  described  forcibly  suggests  such  an  explanation  to  the  most 
casual  observer.  2.  A  closer  examination  confirms  it  by  showing  that 
the  gorge  is  truly  a  valley  of  erosion,  since  the  strata  on  the  two  sides 
correspond  accurately  (see  Fig.  7).  3.  As  already  seen,  the  falls  have 
receded  in  historic  times  at  a  rate  of  from  one  foot  to  three  feet  a  year. 
The  portion  of  the  gorge  thus  formed  under  our  eyes  does  not  differ  in 
any  essential  respect  from  other  portions  farther  down  the  stream.  The 
evidence  thus  far  is  not  perfectly  conclusive  that  the  gorge  was  formed 
by  the  present  river  during  the  present  geologic  epoch,  since  the  gorge 
may  have  been  eroded  during  a  previous  epoch,  and  the  present  river 
found  it,  appropriated  it  as  its  channel,  and  continued  to  extend  it. 
But  (4)  certain  stratified  deposits  have  been  found  by  Mr.  Lyell  and 


FIG.  7.— Ideal  Section  across  Chasm  below  the  Falls. 

others  on  the  upper  margin  of  the  ravine,  containing  shells,  all  of  which 
are  identical  with  the  shells  now  living  in  Niagara  River.  On  the  mar- 
gins of  all  rivers  we  find  stratified  deposits  of  mud  and  sand  containing 
dead  shell.  The  stratified  deposits  found  by  Mr.  Lyell  were  such  mud- 
banks  of  the  Niagara  River  before  the  falls  had  receded  so  far,  and 
therefore  when  the  river  still  ran  on  the  Erie  plateau  at  this  point. 


14:  AQUEOUS  AGENCIES. 

This  is  well  seen  in  the  subjoined  figure,  representing  an  ideal  cross- 
section  of  the  gorge  below  the  falls.  The  dotted  lines  represent  the 
former  bed  and  level  of  the  river ;  a  a  represent  the  banks  of  stratified 
mud  left  on  the  margin  of  the  gorge,  as  the  river  eroded  its  bed  down 
to  its  present  level. 

Other  Falls, — The  evidence  is  completed  by  examination  of  other 
great  falls.  In  almost  all  perpendicular  falls  we  find  a  similar  arrange- 
ment of  strata  followed  by  similar  results.  The  Falls  of  St.  Anthony, 
in  the  Mississippi  River,  are  a  very  beautiful  illustration.  Here  we  find 
a  configuration  of  surface  very  similar  to  that  in  the  neighborhood  of 
Niagara.  Above  the  falls  the  Mississippi  Eiver  runs  on  a  plateau  which 
terminates  abruptly  at  the  mouth  of  Minnesota  River  by  an  escarpment 
about  a  hundred  feet  high.  From  this  escarpment,  backward  through 
the  upper  plateau,  runs  a  gorge  with  perpendicular  sides  nearly  a  hun- 
dred feet  high  for  eight  miles  to  the  foot  of  the  falls.  The  river  above 
the  falls  runs  on  a  hard,  silurian  limestone  rock,  only  a  few  feet  in  thick- 
ness. Beneath  this  is  a  white  sandstone,  so  soft  that  it  can  be  easily 
excavated  with  the  fingers.  This  sandstone  forms  the  walls  of  the  gorge 
as  far  as  the  escarpment.  The  recession  of  the  falls  by  the  undermining 
and  falling  of  the  limestone  is  even  more  evident  than  at  Niagara. 
Tributaries  running  into  the  Mississippi  just  below  the  falls  are,  of 
course,  precipitated  over  the  margin  of  the  gorge.  Here,  therefore,  the 
same  conditions  are  repeated,  and  hence  are  formed  subordinate  gorges, 
headed  by  perpendicular  falls.  Such  are  the  falls  and  gorge  of  Little 
River  (Minnehaha),  which  runs  into  the  Mississippi  about  two  miles 
above  the  mouth  of  the  Minnesota  River. 

Another  admirable  illustration  of  the  conditions  under  which  per- 
pendicular falls  recede  is  found  in  the  falls  of  the  numerous  tributaries 
of  Columbia  River  where  the  great  river  breaks  through  the  Cascade 
Range.  The  Columbia  River  gorge  is  2,500  to  3,000  feet  deep.  The 
walls  consist  of  columnar  basalt  underlaid  near  the  water-level  by  a 
softer  conglomerate.  Every  tributary  at  this  point  emerges  from  a 
deep  gorge,  headed  two  or  three  miles  back  by  a  perpendicular  wall, 
over  which  is  precipitated  the  water  of  the  tributary  as  a  fall  200  to 
300  feet  high.  The  falling  water  erodes  the  softer  conglomerate,  un- 
dermines the  vertical-columned  basalt,  which  tumbles  into  the  stream 
and  is  carried  away ;  and  thus  the  fall  has  worked  back  in  each  case 
about  two  or  three  miles  to  its  present  position.*  All  of  this,  has  taken 
place  during  the  present  geological  epoch,  f 

*  Gilbert  has  shown  (American  Journal,  August,  1876)  that  comparative  freedom 
from  detritus  is  another  condition  of  the  formation  of  perpendicular  waterfalls.  In 
muddy  rivers  commencing  inequalities  are  filled  up  by  sediment,  and  waterfalls  can  not 
be  formed. 

f  American  Journal  of  Science  and  Art,  1874,  vol.  vii,  pp.  167,  259. 


WATERFALLS.  15 

The  wonderful  falls  of  the  Yosemite  Valley,  of  which  there  are  six 
in  a  radius  of  five  miles,  one  of  them  1,600  feet,  three  600  to  700  feet, 
and  two  over  400  feet  high,  seem  to  be  an  exception  to  the  law  given 
above.  Their  perpendicularity  seems  to  be  the  result  of  the  compara- 
tive recency  of  the  evacuation  of  -the  valley  by  an  ancient  glacier,  and 
therefore  the  shortness  of  the  time  during  which  the  rivers  have  been 
falling,  combined  with  the  hardness  of  the  granite  rocks.  The  Yo- 
semite gorge  was  not  made  by  the  present  rivers  during  the  present 
epoch. 

Time  necessary  to  excavate  Niagara  Gorge. — All  attempts  to  esti- 
mate accurately  the  time  consumed  in  excavating  Niagara  gorge  must 
be  unreliable,  since  we  do  not  yet  know  the  circumstances  which  con- 
trolled the  rate  of  recession  at  different  stages  of  its  progress.  Among 
these  circumstances,  the  most  important  are  the  volume  of  water,  and 
especially  the  hardness  of  the  rocks,  and  the  manner  in  which  hard  and 
soft  are  superposed.  The  present  position  of  the  falls  is  apparently 
favorable  for  rapid  recession.  Mr.  Lyell  thinks,  from  personal  observa- 
tion, that  the  average  rate  could  not  have  been  more  than  one  foot  per 
annum,  and  probably  much  less.  At  this  rate  it  would  require  about 
36,000  years.  More  recent  estimates  make  the  probable  rate  three  feet 
a  year,  and  the  time,  therefore,  12,000  years.  But  whether  we  adopt 
the  one  or  the  other  estimate,  this~tmie  must  not  be  confounded  with 
the  age  of  the  earth.  The  work  of  excavating  the  Niagara  chasm  be- 
longs to  the  present  epoch,  and  the  time  is  absolutely  insignificant  in. 
comparison  with  the  inconceivable  ages  of  which  we  will  speak  in  the 
subsequent  parts  of  this  work.  The  Falls  of  St.  Anthony  recedes  about 
five  feet  per  annum,  and  has  made  its  gorge  in  about  8,000  years 
(Wmchell). 

Ravines,  Gorges,  Canons.— We  have  already  seen  (page  12)  that 
ravines,  gorges,  etc.,  are  everywhere  produced  in  mountain-regions  by 
the  regular  operation  of  erosive  agents.  Nowhere  are  examples  more 
abundant  or  more  conspicuous  than  in  our  own  country,  and  especially 
in  the  Western  portion.  On  the  Pacific  slope,  the  most  remarkable  are 
the  gorges  of  the  Fraser  and  of  the  Columbia  Rivers,  fifty  miles  long 
and  several  thousand  feet  deep ;  those  of  the  North  and  South  Forks 
of  the  American  River,  2,000  to  3,000  feet  deep  in  solid  slate ;  the  canon 
of  the  Tuolumne  River,  with  its  Hetchlietchy  Valley ;  the  canon  of  the 
Merced,  with  its  Yosemite  Valley,  with  nearly  vertical  granite  cliffs, 
3,000  to  nearly  5,000  feet  high ;  and,  deepest  of  all,  the  grand  canon 
of  King's  River,  3,000  to  7,000  feet  deep,  in  hard  granite. 

Some  of  these  great  cafions  have  been  forming  ever  since  the  forma- 
tion of  the  Sierra  Range — i.  e.,  since  the  Jurassic  period.  It  is  possible, 
also,  that  in  some  of  them  the  erosive  agents  have  been  assisted  by 
antecedent  igneous  agencies,  producing  fissures,  which  have  been  en- 


16 


AQUEOUS  AGENCIES. 


larged  and  deepened  by  water  and  by  ice.  But  there  are  some,  at  least, 
which  may  be  proved  to  have  been  produced  wholly  by  erosion,  and 
that  during  the  present  or  at  least  during  very  recent  geological  times. 
We  refer  especially  to  those  which  have  been  cut  through  lava-streams. 
In  Middle  and  Northern  California  are  found  lava-streams  which 
have  flowed  from  the  crest  of  the  Sierra.  By  means  of  the  strata  on 
which  they  lie,  these  streams  are  known  to  have  flowed  after  the  end  of 
the  Tertiary  period.  Yet  the  present  rivers  have  since  that  time  cut 


FIG.  8. — Lava-Stream  cut  through  by  Rivers:  a  a,  Basalt;  b  b,  Volcanic  Ashes;  c  c,  Tertiary;  d  d, 
Cretaceous  Rocks.     (From  Whitney.) 

great  cafions  through  the  lava  and  into  the  underlying  rock,  in  some 
cases  at  least  2,000  feet  deep.  Such  facts  impress  us  with  the  immen- 
sity of  geological  times.  This  important  point  is  discussed  more  fully 
in  a  subsequent  part  of  this  work. 


FIG.  9.— Buttes  of  the  Cross  (Powell). 

But  nowhere  in  this  country,  or  in  the  world,  are  the  phenomena  of 
canons  exhibited  on  so  grand  a  scale,  and  nowhere  are  they  so  obviously 
the  result  of  pure  erosion,  as  in  the  region  of  the  Grand  Plateau  of 
Utah,  Arizona,  New  Mexico,  and  Colorado.  This  plateau  is  elevated 
7,000  to  8,000  feet  above  the  sea,  and  composed  entirely  of  nearly  hori- 
zontal strata,  comprising  nearly  the  whole  geological  series  from  the 
Tertiary  downward.  Through  this  series  all  the  streams  have  cut  their 


CANONS,   GORGES,   ETC. 


17 


way  downward,  forming  narrow  canons  with  almost  perpendicular  walls 
several  thousand  feet  deep,  so  that  in  many  parts  we  have  the  singular 
phenomenon  of  a  whole  river-system  running  almost  hidden  far  below 
the  surface  of  the  country,  and  rendering  the  country  entirely  impass- 
able  in  certain  directions  (see  Frontispiece).  Nor  is  the  erosion  con- 


FIG.  10.— Caion  of  the  Colorado  and  its  Tributaries  (from  a  Drawing  by  Newberry). 

fined  to  canons ;  for  the  rain-erosion  has  been  so  thorough  and  general 
that  much  of  the  upper  portion  of  the  plateau  has  been  wholly  carried 
away,  leaving  only  isolated  turrets  (buttes)  or  isolated  level  tables  with 
cliff-like  walls  (mesas)  to  indicate  their  original  height.  All  these  facts 
are  well  shown  in  Fig.  10.  The  explanation  of  these  deep  and  narrow 
canons  is  probably  to  be  found  in  the  predominance  of  stream-erosion 
over  general  disintegration  and  rain-erosion,  which  is  characteristic  of 
an  arid  climate  (Gilbert). 

Chief  among  these  canons  is  the  Grand  Carton  of  the  Colorado,  300 
miles  long  and  3,000  to  6,200  feet  deep,  forming  the  grandest  natural 
geological  section  known.  Into  this  the  tributaries  enter  by  side-ca- 
flons;of  nearly  equal  depth,  and  often  of  extreme  narrowness.  Fig.  11 
represents  the  natural  proportions  of  such  a  cafion. 

Time. — These  remarkable  canons  have  evidently  been  cut  wholly 
by  the  streams  which  now  occupy  them,  and  which  are  still  continuing 
the  work.  The  work,  probably  commenced  in  the  early  Tertiary  with 


18 


AQUEOUS  AGENCIES. 


the  emergence  of  this  portion  of  the  continent,  became  more  rapid  in 
the  latter  portion  of  the  Tertiary  with  the  great  elevation  of  the  plateau, 

and  has  continued  to  the  present  time. 
Thus,  causes  now  in  operation  are  identi- 
fied with  geological  agencies. 

In  the  Appalachian  chain  gorges  and 
valleys  of  erosion  are  abundant,  but  the 
evidences  of  present  action  are  less  obvi- 
ous, and  therefore  we  defer  their  treat- 
ment to  Part  II,  for  we  are  now  discussing 
agencies  still  in  operation.  Among  the 
more  remarkable  narrow  gorges  in  this 
region,  we  may  mention,  in  passing,  the 
Tallulali  Eiver  gorge,  several  miles  long 
and  nearly  1,000  feet  deep,  in  Rabun 
County,  Georgia,  and  the  gorge  of  the 
French  Broad  in  North  Carolina.  The 
general  effects  of  erosion  will  be  more 
fully  treated  under  Mountain  Sculpture 
(page  255). 

Transportation  and  Distribution  of 
Sediments. 


The  specific  gravity  of  most  rocks  is 
about  2  '5.  Immersed  in  water,  they  there- 
fore lose  nearly  half  their  weight.  This 
fact  greatly  increases  the  transporting 
power  of  water.  The  actual  transport- 
ing power  of  water  is  determined  partly 
by  experiment  and  partly  by  reasoning  on  the  general  laws  of  force. 
By  experiment  we  determine  the  transporting  power  under  a  given  set 
of  circumstances :  by  general  reasoning  we  determine  its  law  of  varia- 
tion, and  apply  the  data  given  by  experiment  to  every  possible  case. 

Experiments. — It  has  been  found  by  experiment  that  a  current, 
moving  at  the  rate  of  three  inches  per  second,  will  take  up  and  carry 
along  fine  clay  ;  moving  six  inches  per  second,  will  carry  fine  sand ; 
eight  inches  per  second,  coarse  sand,  the  size  of  linseed  ;  twelve  inches, 
gravel ;  twenty-four  inches,  pebbles ;  three  feet,  angular  stones  of  the 
size  of  a  hen's  egg.*  It  will  be  readily  seen  from  the  above  that  the 
carrying-poiver  increases  much  more  rapidly  than  the  velocity.  For 
instance,  a  current  of  twelve  incites  per  second  carries  gravel,  while  a 
current  of  three  feet  per  second,  only  three  times  greater  velocity, 


PIG.  11.— Section  of  the  Virgen  River 
(after  Gilbert). 


*  Page's  Geology,  p.  28 — Rankine. 


TRANSPORTATION   AND   DISTRIBUTION   OF  SEDIMENTS.  19 

carries  stones  many  hundred  times  as  large  as  grains  of  gravel.  Let  us 
investigate  the  law. 

Law  of  Variation.— If  the  surface  of  the  obstacle  is  constant,  the., 
force  of  running  water  varies  as  the  velocity  squared  :  /  a  v2  (1).  This' 
may  be  easily  proved.  Suppose  we  have  an  obstacle  like  the  pier  of  a 
bridge,  standing  in  water  running  with  any  given  velocity.  Now, 
if  from  any  cause  the  velocity  of  the  current  be  doubled,  since  mo- 
mentum or  force  is  equal  to  quantity  of  matter  multiplied  by  velocity 
(M  =  Q  X  V),  the .force  of  the  current  will  be  quadrupled,  for  there 
will  be  double  the  quantity  of  waterjstriking  the  pier  in  a  given  time 
with  double  the  velocity.  If  the  velocity  of  the  current  be  trebled, 
there  will  be  three  times  the  quantity  of  matter  striking  with  three 
times  the  velocity,  and  the  force  will  be  increased  nine  times.  If  the 
velocity  be  quadrupled,  the  force  is  increased  sixteen  times,  and  so  on. 

Next,  if  the  velocity  of  the  current  remains  constant,  while  the  size 
of  the  opposing  obstacle  varies,  then  evidently  the  force  of  the  current 
will  vary  as  the  opposing  surface :  if  the  opposing  surface  is  doubled, 
the  force  is  doubled  ;  if  trebled,  the  force  is  trebled,  etc.  But  in  similar 
figures,  surfaces  vary  as  the  square  of  the  diameter.  Therefore,  in  this 
case,  force  varies  as  diameter  squared  :  f1  oc  dz  (2).  Therefore,  when 
both  the  velocity  of  the  current  and  the  size  of  the  stone  or  other 
obstacle  vary,  then  the  force  varies  as  the  square  of  the  velocity  of 
the  current  multiplied  by  the  square  of  the  diameter  of  the  s'tone  : 
F(xv2xd2(3). 

This  last  equation  gives  the  law  of  variation  of  the  moving  force. 
But  the  resistance  to  be  overcome,  or  the  tveight  of  the  stone,  varies 
as  the  cube  of  the  diameters :  W  oc  d*.  We  have,  therefore,  both  the 

law  of  the  moving  force  and  the  law  of  the  resistance :  j  jJ*  v  %     ' 

Now  the  case  we  wish  to  consider  is  that  in  which  the  current  is  just 
able  to  move  the  stone,  or  when  F  oc  W.  In  this  case  d*  cc  v*  X  d*, 
or  d  oc  v*.  Substituting,  in  the  third  equation,  for  d  its  value, 
F  oc  v1  X  v*  =  v'.  We  place  these  equations  together,  so  that  they 
may  be  better  understood  : 

When  surface  =  constant         .         .         .  /  oc  c*  (1) 

When  velocity  =  constant       .         .         .  /'  a  d?  (2) 

When  both  vary F  oc  u2  x  ^  (3) 

But W  a  d3 

And  when  W  a  F,  then .         .         .         .  d3  a  «a  x  d* 

Dividing  by  d* d  oc  «* 

Substituting  in  3      .  •      .         .         .         .  F  oc  «3  x  v4 

Or F  oc  v9 

That  is,  the  transporting  power  of  a  current  or  the  weight  of  the  largest 
fragment  it  can  carry,  varies  as  the  sixth  power  of  the  velocity.  This 


I 


O 


FIG.  12. 


20  AQUEOUS  AGENCIES. 

seems  so  extraordinary  a  result  that,  before  accepting  it,  we  will  try  to 

make  it  still  clearer  by  an  example. 

Let  a  (Fig.  12)  represent  a  cubic  inch  of  stone,  which  a  current  of 

a  certain  velocity  will  just  move.     Now,  the  proposition  is  that,  if  the 

velocity  of  the  current  be  doubled,  it  will 
move  the  stone  Z>,  sixty-four  times  as  large. 
That  it  would  do  so  is  evident  from  the 
fact  that  the  opposing  surface  of  b  is  sixteen 
times  as  great  as  that  of  a,  and  the  moving 
force  would  be  increased  sixteen  times  from 
this  cause.  But  the  velocity  being  double, 
as -we  have  already  seen,  the  force  against 

\every  square  inch  of  Z»  will  now  be  four  times 
that  previously  against  a,  and,  therefore,,  the 
>w  whole  force  from  these  two  causes  would 
belGX^^Gl  times  as  great.  But  the 
weight  is  also  sixty-four  times  as  great; 
therefore,  the  current  would  be  just  able  to  move  it.  We  may  accept 
it,  therefore,  as  a  law,  that  the  transporting  power  varies  as  the  sixth 
power  of  the  velocity.  If  the  velocity,  therefore,  be  increased  ten 
times,  the  transporting  power  is  increased  1,000,000  times. 

We  have  seen  that  a  current  running  three  feet  per  second,  or  about 
two  miles  per  hour,  will  move  fragments  of  stone  of  the  size  of  a  hen's 
egg,  or  about  three  ounces'  weight.  It  follows  from  the  above  law  that 
a  current  of  ten  miles  an  hour  will  carry  fragments  of  one  and  a  half 
ton,  and  a  torrent  of  twenty  miles  an  hour  will  carry  fragments  of  100 
tons'  weight.  We  can  thus  easily  understand  the  destructive  effects  of 
mountain-torrents  when  swollen  by  floods. 

The  transporting  power  of  water  must  not  be  confounded  with  its 
erosive  power.  The  resistance  to  be  overcome  in  the  one  case  is  weight, 
in  the  other  cohesion  ;  the  latter  varies  as  the  square,  the  former  as  the 
sixth  power  of  the  velocity.  In  many  cases  of  removal  of  slightly  coher- 
ing material  the  resistance  is  a  mixture  of  these  two  resistances,  and  the 
power  of  removing  material  will  vary  at  some  rate  ^between  #a  and  v6. 

There  are  certain  corollaries  which  follow  from  the  above  law : 

A.  If  a  current  bearing  sediment  have  its  velocity  checked  by  any 
cause,  even  in  a  slight  degree,  a  comparatively  large  portion  of  the  sedi- 
ment is  immediately  deposited.  But  if,  on  the  other  hand,  the  velocity 
of  a  current  be  increased  by  any  cause,  in  never  so  small  a  degree,  it 
will  again  take  up  and  carry  on  materials  which  it  had  deposited  ;  in 
other  words,  it  will  erode  its  bed  and  banks ;  and  these  effects  are  sur- 
prisingly large  on  account  of  the  great  change  in  erosive  and  transport- 
ing power,  with  even  slight  changes  of  velocity. 

BI  Water,  whether  still  or  running,  has  a  wonderful  power  of  sorting 


RIVERS  SEEK  THEIR  BASE-LEVEL.  21 

materials.  If  heterogeneous  material,  such  as  ordinary  earth,  consisting 
of  grains  of  all  sizes,  from  pebbles  to  the  finest  clay,  be  thrown  into 
still  water,  the  coarse  material  sinks  first  to  the  bottom,  and  then  the  next 
finer,  and  the  next,  and  so  on,  until  the  finest  clay,  falling  last,  covers 
the  whole.  In  running  water  the  same  sorting  takes  place  even  more 
perfectly,  only  the  different  kinds  of  materials  are  not  dropped  upon 
one  another,  but  successively  farther  and  farther  down  the  stream  in  the 
order  of  their  fineness.  This  property  we  will  call  the  sorting  power  of 
ivater.  Advantage  is  often  taken  of  this  property  in  the  arts  to  separate 
materials  of  different  sizes  or  specific  gravities.  By  this  means  grains 
of  gold  are  separated  from  the  gravel  with  which  it  is  mingled,  and 
emery  or  other  powders  are  separated  into  various  degrees  of  fineness. 

We  will  now  apply  the  foregoing  simple  principles  in  the  explana- 
tion of  all  the  phenomena  of  currents. 

1. — Relation  of  Current-  Velocity  to  Erosion  and  Sedimentation. 

The  force  of  a  current  is  consumed  in  two  ways,  viz.,  by  transporta- 
tion and  erosion.  If  the  current  is  full-loaded,  its  whole  force  is  con- 
sumed in  transportation  and  none  is  left  over  for  erosion.  Such  a  river 
will  neither  erode  nor  deposit.  If  under-loaded,  the  river  will  erode  ; 
if  overloaded,  it  will  deposit.  Thus  a  current  of  pure  water  will  erode 
but  little,  because  it  carries  no  graving-tools.  If  we  add  sand  and 
gravel,  the  erosion  will  increase  to  a  maximum,  beyond  which  it  again 
decreases,  because  more  and  more  force  is  consumed  in  carrying,  and 
less  and  less  is  left  over  for  erosion ;  until  finally,  in  the  full-loaded  stream, 
erosion  ceases  and  sedimentation  begins.  Thus  the  Platte  and  Colorado 
Rivers  have  about  the  same  slope  and  velocity ;  but  while  the  Colorado 
is  deepening  its  channel,  the  Platte  on  the  whole,  remains  about  the 
same  level,  sometimes  cutting,  sometimes  depositing.  The  Colorado  is 
under-loaded,  the  Platte  full-loaded.  Again :  the  Feather  River,  during 
floods,  is  overloaded,  and  builds  up  by  deposit.  During  low  water  it 
scours  out  what  was  previously  deposited,  even  though  its  velocity  is 
much  less. 

2. — Rivers  seek  their  Base-Level. 

The  level  at  which  a  river  neither  cuts  nor  deposits  is  called  its[ 
base-level.  Every  river  is  seeking  this  level.  If  above  it,  it  seeks  it 
by  cutting ;  if  below  it,  it  seeks  it  by  building  up  by  sedimentation. 
Rivers  thus  become  delicate  indicators  of  up  or  down  movements  of 
land-surfaces.  Suppose  a  continent  to  rise  gradually  and  then  remain 
steady;  all  the  rivers  would  immediately  increase  their  velocity  and 
begin  to  cut.  Now,  in  making  the  resulting  gorge,  two  processes  are 
going  on,  viz.,  a  cutting  downward  by  the  river,  and  a  widening  out  by 
cliff-crumbling  and  rain-wash.  A  V-shaped  caflon  is  thus  usually 
formed,  whose  shape,  whether  sharp  or  wide,  will  depend  on  the  relative 


22 


AQUEOUS  AGENCIES. 


rate  of  these  two  processes.  They  would  continue,  however,  to  cut  deeper 
and  deeper,  until  they  finally  reached  their  base-level.  Then  they  would 
cut  no  deeper,  but  sweep  from  side  to  side,  widening  their  channels. 
Meanwhile,  rain- wash  would  continue  to  cut  down  their  divides.  Thus 
wide  channels  and  low  divides,  or  rounded  and  sweeping  curves,  are  very 
characteristic  of  old  topography,  while  deep  and  narrow  gorges  and 
cafions  are  a  sign  of  recent  elevation,  and  therefore  comparatively  new 
topography.  Moreover,  successive  movements  are  each  faithfully  re- 
corded. Thus  Fig.  13,  which  is  a  section  across  the  Grand  Canon  of 

the  Colorado,  shows  the 
following  events :  1.  The 
plateau  region  was  raised 
and  the  river  cut  down 
3,000  feet,  and  reached  its 
base-level.  2.  The  river 
sweeping  from  side  to  side, 
and  the  crumbling  of  the  cliffs,  gradually  widened  the'  cafion  to  its 
width  in  the  upper  part,  b  b.  3.  Another  rise  occurred,  and  the  river 
again  cut  3,000  feet  more,  and  made  the  inner  gorge,  a  a.  This  second 
rise  is  so  recent  that  the  river  has  not  yet  reached  its  base-level. 

On  the  other  hand,  suppose  a  continent,  by  sinking,  carries  its 
river-beds  below  their  base-level :  then  the  decreasing  slope  will  check 
the  velocity  of  the  current,  and  the  rivers  will  immediately  begin  to 
build  up  again  by  sedimentation  until  they  again  reach  their  base-level. 
For  example,  in  the  Mississippi  River  the  following  events  are  recorded  : 
1.  A  higher  condition  of  land,  during  which  it  reached  its  base-level, 
and  formed  the  broad  trough  r"  r"  r".  2.  A  subsidence  of  land  and  a 


FIG.  13.— Ideal  Section  across  Grand  Canon  (after  Button): 
a  a,  inner  gorge;  b  b,  outer  cafion  walls. 


FIG.  14.— Generalized  Section  across  the  Mississippi  River:  r"  r"  r" ,  old  bed;  r'  r',  second  bed;  r, 
present  bed;  d'  d',  old  deposits;  d  d,  present  deposits. 

building  up  by  sedimentation  d'  to  the  level  1 1.  3.  A  partial  re-eleva- 
tion and  a  cutting  down  200  feet,  to  the  level  r'  r'.  4.  A  resinking 
and  building  by  alluvial  deposit  d  of  about  50  feet.  Thus,  while  on  coast- 
lines, old  sea-margins  are  indicators  of  crust  movements,  in  the  interior 
of  continents  river-channels  may  be  used  for  the  same  purpose. 

3. — Stratification. 

We  have  seen  that  heterogeneous  material  thrown  into  still  water  is 
completely  sorted.     This  is  not  stratification,  since  the  various  degrees 


WINDING  COURSE  OF  RIVERS.  23 

of  fineness  graduate  insensibly  into  one  another.  But,  if  we  repeat  the 
experiment,  the  coarsest  material  will  fall  upon  the  finest  of  the  previ- 
ous experiment,  and  then  graduate  similarly  upward.  If  we  examine 
the  deposit  thus  made,  we  observe  a  distinct  line  of  junction  between 
the  first  and  the  second  deposit.  This  is  stratification,  or  lamination. 
For  every  repetition  of  the  experiment  a  distinct  lamina  is  formed.  It 
is  evident,  therefore,  that  to  produce  stratification  two  conditions  are 
necessary,  namely :  1.  An  heterogeneous  material ;  and,  2.  An  inter- 
mittently acting  cause.  Now,  these  two  conditions  are  always  present 
in  Nature  where  sediments  are  depositing.  Into  every  body  of  still 
water,  as  a  lake  or  sea,  rivers  bring  heterogeneous  material  torn  from 
the  land ;  but  this  process  is  not  equable,  being  increased  in  the  case  of 
small  streams  by  every  rain,  and  in  large  rivers  by  the  annual  floods. 
Therefore,  sedimentary  deposits  in  still  water  are  always  stratified. 

In  running  water^tfie  case  is  somewhat  different.  If  the  stream 
runs  with  a  velocity  at  all  times  the  same,  then  with  every  repetition 
of  the  foregoing  experiment  the  same  kind  of  material  falls  on  the 
same  spot — gravel  on  gravel,  sand  on  sand,  and  mud  on  mud — and 
there  will  be  no  stratification.  In  running  water,  therefore,  another 
condition  is  necessary,  namely,  a  variable  current.  For,  when  the 
velocity  increases,  coarser  material  will  be  carried  and  deposited  where 
finer  was  previously  deposited ;  when  the  velocity  decreases,  finer  will 
be  deposited  on  coarser,  and  very  perfect  stratification  is  the  result. 
Now,  these  three  conditions  are  always  present  in  every  natural  cur- 
rent. The  velocity  of  every  river-current  varies  not  only  very  greatly 
in  different  portions  of  the  year,  as  in  seasons  of  low  water  and  seasons 
of  flood,  but  also  (from  the  constant  shifting  of  the  subordinate  cur- 
rents of  the  stream)  from  day  to  day,  from  hour  to  hour,  and  even 
from  moment  to  moment.  It  follows,  therefore,  that  deposits  in  run- 
ning water  are  also  always  stratified.  Sometimes  extreme  beauty  and 
distinctness  of  stratification  in  the  deposits  of  large  rivers  are  due  to 
the  fact  that  the  different  branches  flood  at  different  seasons,  and  bring 
down  differently  colored  sediments. 

We  may,  therefore,  announce  it  as  a  law,  that  all  sedimentary  de- 
posits are  stratified;  and,  conversely,  that  all  stratified  masses  in 
which  the  stratification  is  the  result  of  sorted  material  are  sedimentary 
in  their  origin.  Upon  this  law  is  founded  almost  all  geological  rea- 
soning. 

4. —  Winding  Course  of  Rivers. 

The  winding  course  of  rivers  is  duejgartly  to  erosion  and  partly  to 
sedimentary  deposit.     It  is  most  conspicuous  and  most  easily  studied 
~TTrriYers  which  run  through  extensive  alluvial  deposit.     If  the  chan- 
nel of  such  a  river  be  made  perfectly  straight  by  artificial  means,  very 
soon  some  portion  of  the  bank  a  little  softer  than  the  rest  will  be  exca- 


AQUEOUS  AGENCIES. 


vated  ;  this  will  reflect  the  current  obliquely  across  to  the  other  side, 
which  will  become  similarly  excavated.  Thus  the  current  is  reflected 
from  side  to  side,  increasing  the  excavations.  In 
the  mean  time,  while  erosion  is  progressing  on  the 
outer  side  of  the  curves,  because  the  current  is 
swiftest  there,  deposit  is  taking  place  on  the  inner 
side,  because  there  the  current  is  slowest  :  thus, 
while  the  outer  curve  extends  by  erosion,  the  in- 
ner curve  extends,  pari  passu,  by  deposit  (Fig. 
15),  and  the  winding  continues  to  increase,  until, 
under  favorable  circumstances,  contiguous  curves 
on  the  same  side  run  into  each  other,  as  at  a  #, 
and  the  curve  c  on  the  other  side  is  thrown  out 
and  silted  up.  Thus  are  formed  the  crescentic 
lakes  or  lagoons  (I  I)  so  common  in  the  swamps  of 
great  rivers.  They  are  abundant  in  the  swamps 
of  all  the  Gulf  rivers,  especially  the  Mississippi. 
They  are  old  beds  of  the  river,  thrown  out  and 
silted  up  in  the  manner  indicated  above. 

5.  —  Flood-Plain  Deposits. 

All  great  rivers  annually  flood  portions  of 
level  land  near  their  mouths,  and  cover  them  with 
sedimentary  deposits.  The  whole  area  thus 
flooded  is  called  the  flood-plain.  These  flood- 
plains  are  very  extensive,  and  the  deposits  very 
large,  in  the  case  of  rivers  rising  in  lofty  mount- 
ains and  flowing  in  the  lower  portion  of  their 
course  through  extensive  tracts  of  flat  country. 
In  the  lofty  mountains  the  current  runs  with 
great  velocity,  and  gathers  abundant  sediment  ;  on  reaching  the  flat 
country  the  velocity  is  checked,  the  river  overflows,  and  the  sediment 
is  deposited.  The  flood-plain  of  the  Mississippi  River  is  30,000  square 
miles.  The  flood-plain  of  the  Nile  is  the  whole  land  of  Egypt. 

The  flood-plain  of  a  river  may  be  divided  into  two  parts,  viz.,  the 
river-swamp  and  the  delta.  The  river-swamp  is  that  part  which  was 
originally  land-surface  ;  the  delta,  that  part  which  has  been  reclaimed 
from  the  sea  or  lake  by  the  river.  We  will  take  up  these  in  succession. 
River-Swamp.  —  We  have  already  seen  that,  with  every  recurrence 
of  the  rainy  season  or  of  the  melting  of  snows,  the  flooding  and  the 
deposition  of  sediment  are  repeated.  Thus  the  river-swamp  deposit 
increases  in  thickness,  and  the  level  of  the  whole  flood-plain  rises  con- 
tinually. Fig.  16  is  an  ideal  section  showing  the  manner  in  which  the 
flood-plain  is  successively  built  up  :  a  a  a  is  the  supposed  original  con- 


River- 


FLOOD-PLAIN   DEPOSITS.  25 

figuration  of  the  surface,  #  b  the  successive  levels  of  deposit,  e  the  level 
of  the  river  at  low  water,  and  /  i  the  level  of  flood- water. 


FIG.  16.— Ideal  Section  of  a  River  subject  to  Floods. 

The  extent  of  such  river-swamp  deposits  is  sometimes  very  great. 
The  river-swamp  of  the  Nile  constitutes  the  whole  fertile  land  of  Egypt 
above  the  delta.  The  river-swamp  of  the  Mississippi  River,  or  its 
flood-plain  exclusive  of  the  delta,  extends  from  fifty  miles  above  the 
mouth  of  the  Ohio  to  the  head  of  the  delta,  a  distance  of  about  five 
hundred  miles ;  its  average  width  is  over  thirty  miles,  and  it  includes 
an  area  of  16,000  square  miles.  It  is  bounded  on  either  side  by  high 
bluffs  belonging  to  a  previous  geological  period.  The  depth  of  this 
deposit  at  the  head  of  the  delta  is  assumed  by  Lyell  to  be  264  feet.* 
But  Ijilgard  has  shown  that  but  a  small  portion  of  this  is  alluvium  or 
river  deposit  of  the  present  epoch. 

Natural  Levies. — It  is  seen  by  the  cross-section  (Fig.  16)  that  the 
level  of  the  river-swamp  slopes  gently  from  the  river  outward,  so  that 
the  river  is  bounded  on  each  side  by  a  higher  ridge,  d  d.  The  material 
of  this  ridge  is  coarser  than  that  of  the  swamp  farther  back.  Such 
natural  levees  are  found  along  all  rivers  subject  to  regular  overflows. 
They  are  formed  as  follows :  In  times  of  flood  the  whole  flood-plain  is 
covered  with  water  moving  slowly  seaward.  Through  the  midst  of 
this  wide  expanse  of  water  runs  the  rapid  current  of  the  river.  Now, 
on  either  side,  just  where  the  rapid  current  of  the  river  comes  in  con- 
tact with  the  comparatively  still  water  of  the  flood-plain,  and  is  checked 
by  it,  a  line  of  abundant  sediment  is  determined,  which  forms  the  natu- 
ral levee.  Except  in  very  high  freshets,  these  natural  ridges  are  not 
entirely  covered,  so  that  the  river  in  ordinary  floods  is  often  divided 
into  three  streams,  viz.,  the  river  proper  and  the  river-swamp  water  on 
either  side.  They  can  not,  however,  confine  the  river  within  its  bank 
and  prevent  overflows,  since  the  river-bed  is  also  constantly  rising  by 
deposit.  Thus  the  river-bed,  the  natural  levee,  and  the  river-swamp, 
all  rise  together,  maintaining  a  certain  constant  relation  to  one  an- 
other. 

Artificial  Levies. — This  constant  relation  is  interfered  with  by  the 
construction  of  artificial  levees.  These  are  constructed  for  the  purpose 
of  confining  the  river  within  its  banks,  and  thus  reclaiming  the  fertile 

*  Lyell,  Principles  of  Geology,  vol.  i,  p.  462. 


26  AQUEOUS  AGENCIES. 

lands  of  the  river-swamp.  As  the  bed  of  the  river  continues  to  rise 
by  deposit,  the  levees  must  be  constantly  elevated  in  proportion ;  but 
the  river-swamp,  being  deprived  of  its  share  of  deposit,  does  not  rise. 
Thus,  under  the  combined  effect  of  human  and  river  agencies  contend- 
ing for  mastery,  an  ever-increasing  embankment  is  formed,  until  finally 
the  river  runs  in  an  aqueduct  elevated  far  above  the  surrounding  plain. 
This  is  very  remarkably  the  case  with  the  river  Po,  which  is  said  to  run 
in  a  channel  that  has  been  thus  elevated  above  the  tops  of  the  houses 
in  the  town  of  Ferrara.  Fig.  17  is  an  ideal  cross-section  of  a  river  and 


FIG.  17. 

flood-plain,  left  at  first  to  the  action  of  natural  causes  for  a  time,  but 
afterward  interfered  with  by  the  construction  of  artificial  levees.  The 
dotted  strata  show  the  work  of  Nature,  and  the  nndotted  the  work  of 
man.  It  is  easy  to  see  that  the  destructive  effects  of  overflow  from 
accidental  crevasses  become  greater  and  greater  with  the  elevation. 
The  Po  has  thus  several  times  broken  through  its  levees  and  deserted 
its  bed,  destroying  several  villages.  The  best  examples  of  rivers  suc- 
cessfully leveed  are  those  of  Italy  and  Holland.  The  Mississippi  has 
never  been  successfully  leveed ;  but,  if  it  should  be,  it  would  commence 
to  build  up  a  similar  aqueduct,  until  the  whole  bed  of  the  river  would 
finally  rise  above  the  level  of  the  river-swamp.* 

6.— Deltas. 

Deltas  are  portions  of  land  situated  at  the  mouths  of  rivers,  and 
reclaimed  from  the  sea  ~by  their  agency.  Over  the  flat  surface  of  the 
delta  the  river  runs  by  inverse  ramification,  and  empties  by  many 
mouths.  They  are  usually  of  irregular  triangular  form,  the  apex  of 
the  triangle  pointing  up  the  stream.  The  delta  of  the  Nile  (Fig.  18) 
is  perhaps  the  best  example  of  the  typical  form.  As  seen  in  the  figure, 
at  the  head  of  the  delta  the  river  divides  into  branches,  and  communi- 
cates with  the  sea  by  many  mouths.  The  area  of  land  thus  made  va- 
ries with  the  size  of  the  river,  the  proportion  of  sediment  in  its  waters, 
and  the  time  it  has  been  making  sedimentary  accumulations.  The 

*  It  is  probable  that  the  effect  of  levees  in  raising  the  river-bed  has  been  greatly  ex- 
aggerated. Recent  observations  on  the  Po  seem  to  show  that  the  elevation  is  confined 
to  the  upper  reaches  of  the  flood-plain  region,  being  prevented  hi  the  lower  course  by 
the  increased  velocity  of  the  current  produced  by  levees. 


DELTAS. 


FIG.  18.— Delta  of  the  Nile. 


delta  of  the  Nile  is  100  miles  long  and  200  miles  wide  at  its  base ;  that 
of  the  Ganges  and  Brahmapootra  is  220  miles  long  and  200  miles  wide 
at  its  base,  comprising  an  area  of  20,000  square  miles.  The  delta  of 
the  Mississippi  (Fig.  19)  is  very  irregular  in  form,  and  is  an  admirable 


Fio.  19.— Delta  of  the  Mississippi. 


AQUEOUS  AGENCIES. 


illustration  of  the  manner  in  which  each  mouth  pushes  its  way  into 
the  sea.  Its  area  is  estimated  at  12,300  square  miles.  The  materials 
of  which  deltas  are  composed  are  usually  the  finest  sands  and  clays,  all 
the  coarser  materials  having  been  deposited  higher  up  the  stream. 

Deltas  are  formed  only  in  lakes  and  tideless  or  nearly  tideless  seas. 
In  tidal  seas,  the  sediments  brought  down  by  the  rivers  are  swept 
away  and  carried  to  sea  by  the  retreating  tide ;  and  instead  of  the  land 
encroaching  upon  the  domain  of  the  sea  by  the  formation  of  deltas, 
the  sea  encroaches  upon  the  land  by  the  erosive  action  of  the  tides,  and 
forms  bays  or  estuaries.  Thus  in  tideless  seas  or  lakes  the  rivers  empty 
by  many  slender  mouths,  while  in  tidal  seas  they  empty  by  wide  bays : 
thus,  for  example,  all  the  rivers  emptying  into  the  great  Canadian 
lakes,  and  all  the  rivers  emptying  into  the  Gulf  of  Mexico,  form 
deltas,  while  all  the  rivers  emptying  into  the  Atlantic  in  both  North 
and  South  America  form  estuaries.  In  Europe  all  the  rivers  emptying 
into  the  Black,  the  Caspian,  the  Mediterranean,  and  the  Baltic,  form 
deltas,  while  those  emptying  into  the  Atlantic  form  estuaries. 

Process  of  Formation.— The  process  of  formation  of  a  delta  may 
be  best  studied  by  observing  it  on  a  small  scale,  in  the  case  of  stream- 
lets running  into  ponds.  In  such  cases  we  observe  always  a  sand  or 
mud  flat  at  the  mouth  of  the  streamlet,  evidently  formed  by  the  sand 
and  clay  brought  down  by  the  current.  As  soon  as  the  current  strikes 
the  still  water  of  the  pond,  its  velocity  is  checked,  and  its  burden  of 
sediment  is  deposited.  Through  the  sand-flat  thus  formed  the  stream- 
let ramifies,  as  seen  in 
Fig.  20.  The  ramifica- 
tion seems  to  be  the  re- 
sult of  the  choking  of 
the  stream  by  its  own 
deposit,  which  forces  it 
to  seek  new  channels. 
The  sand-flat  is  gradu- 
ally extended  farther  and  farther  into  the  pond  by  successive  deposits, 
as  shown  in  Fig.  20.  Fig.  21  shows  the  irregular  stratified  appearance 
of  the  deposits  as  seen  on  cross-section.  In  all  such  cases  of  streams 
flowing  into  ponds  or  lakes,  the  stream  flows  in  at  a  muddy,  but  flows 
out  at  b  perfectly  clear,  having  deposited  all  its  sediment  in  the  pond 
or  lake.  Evidently  if  this  process  continues  without  interruption,  the 
pond  will  eventually  be  filled  up,  after  which,  of  course,  the  sediment 
will  be  carried  farther  down  the  stream.  In  this  manner  small  mount- 
ain-lakes are  often  entirely  filled  up.  The  Rhone  flows  into  Lake 
Geneva  a  turbid  stream,  but  flows  out  beautifully  transparent.  The 
whole  of  its  sediment  is  deposited  where  it  enters  the  lake,  and  it  has 
there  formed  a  delta  six  miles  long.  We  may  confidently  look  forward 


FIG.  20. 


DELTAS.  29 

to  the  time,  though  many  thousand  years  distant,  when  this  lake  will 
be  entirely  filled  up.     After  leaving  the  lake  the  Rhone  again  gathers 


sediment  from  tributaries  flowing  in  below  the  lake,  and  forms  another 
delta  where  it  empties  into  the  Mediterranean.  Many  examples  of 
lakelets  partially  filled,  or  entirely  filled  and  converted  into  meadows, 
are  found  among  the  Sierra  Mountains. 

In  the  section  view  (Fig.  21)  we  have  represented  the  strata  as 
irregular  and  highly  inclined.  This  is  called  oblique  lamination.  This 
can  only  occur  when  a  rapid  stream,  bearing  abundant  coarse  material, 
rushes  into  still  water.  But,  in  the  case  of  large  rivers  flowing  long 
distances  and  bearing  only  the  finest  sediment,  the  stratification  is 
much  more  regular  and  nearly  horizontal. 

Rate  of  Growth. — There  have  been  several  attempts  to  estimate  the 
rate  of  growth  of  deltas,  in  order  to  base  thereon  an  estimate  of  their 
age.  The  delta  of  the  Rhone  in  Lake  Geneva  has  advanqed  at  least 
one  and  a  half  mile  since  the  occupation  of  that  country  by  the  Romans ; 
for  the  ancient  town  Porta  Valesia  (now  Port  Valais),  which  stood  then 
on  the  margin  of  the  lake,  is  now  one  and  a  half  mile  inland.  The 
delta  of  the  same  river  at  its  mouth  in  the  Mediterranean  is  said  to 
have  advanced  twenty-six  kilometres,  or  sixteen  miles,  since  400  B.  c., 
or  thirteen  miles  during  the  Christian  era.*  The  delta  of  the  Po  has 
advanced  twenty  miles  since  the  time  of  Augustus;  for  the  town  Adria, 
a  seaport  at  that  time,  is  now  twenty  miles  inland.  But  the  most  elab- 
orate observations  have  been  made  on  the  Mississippi.  This  river,  as 
seen  in  Fig.  19,  has  pushed  its  way  into  the  Gulf  in  a  most  extraor- 
dinary manner.  According  to  Thomassy,t  and  also  Humphrey  and 
Abbot,  the  rate  of  advance  is  about  one  mile  in  sixteen  years.  The 
rate  of  progress  in  the  deltas  mentioned  has,  however,  probably  not 
been  uniform.  There  are  special  reasons  for  their  more  rapid  advance 
at  the  present-  time.  In  the  case  of  the  Po,  the  successful  leveeing  of 
this  river  has  transferred  to  the  sea  the  whole  of  the  sediment  which 
would  otherwise  have  been  spread  over  the  flood-plain.  In  the  case  of 
the  Mississippi,  for  many  centuries  the  principal  portion  of  the  deposit 
has  been  confined  to  a  narrow  strip  but  a  few  miles  wide,  and  the  ad- 
vance has  been  proportionately  rapid.  For  this  reason  the  river  has 

*  Archives  des  Sciences,  vol.  li,  p.  157.  f  G6ologie  pratique  de  la  Louisiane. 


30 


AQUEOUS  AGENCIES. 


ran  out  to  sea  for  more  than  fifty  miles,  confined  only  by  narrow  strips 
of  land,  the  continuation  of  the  natural  levees.  These  marginal  ridges 
are  continued  as  submarine  banks  even  much  beyond  the  present 
mouths  of  the  river.  The  rate  of  advance  of  the  Nile  delta  seems  to  be 
much  slower. 

Age  of  River-Deposits. — The  age  of  river-swamp  deposits  may  be 
estimated  by  determining  their  absolute  thickness  and  their  rate  of 
increase.  The  river  Nile  is  peculiarly  adapted  for  estimates  of  this 
kind,  because  we  have  on  its  alluvial  deposits  thereat  of  the  oldest 
civilization  and  the  oldest  known  monuments  of  human  art.  These 
monuments,  the  ages  of  which  are  approximately  known,  are  many 
of  them  more  or  less  buried  in  the  river-deposit.  At  Memphis,  the 


FIG.  22.— Ideal  Section  of  Delta  and  Submarine  Bank. 

foundation  of  the  colossal  statue  of  Rameses  II,  over  3,000  years  old, 
was  found  in  1854,  buried  about  nine  feet  in  river-deposit.*  This 
makes  the  rate  of  increase  of  the  deposit  three  and  a  half  inches  per 
century.  Experiments  at  Heliopolis  bring  out  nearly  the  same  result. 
The  whole  depth  of  the  alluvial  deposit  at  Memphis  was  found  to  be 
about  forty  feet,  which,  at  the  above  rate,  would  make  the  age  of  the 
deposit  at  this  point  about  13,500  years.  But  this  all  belongs  to  the 

human  epoch,  for  bricks  have 
been  found  beneath  the  lowest 
part.     The   alluvial  deposit  of 
''-...___  the  Nile   is  much   thicker   at 

some  points   than   forty   feet ; 
but,  on  the  other  hand,  the  rate 
of  increase  for  different  places 
J         \     is  probably  variable. 

;  The  age  of  a  delta  is  usually 
estimated  by  dividing  the  cubic 
contents  of  the  delta  by  the 
annuaj  mud-discharge.  The 
cubic  contents  of  the  delta  are 
estimated  by  multiplying  the 
superficial  area  by  the  mean 

tto.28.-Delta  and  Submarine  Bank.  dePth'        The     m6an    dePth    °f 

the  Mississippi  Delta,  as  deter- 
mined by  borings,  is  taken  by  Mr.  Lyell  as  528  feet,  the  superficial  area 


*  Philosophical  Magazine,  vol.  xvi,  p.  225. 


ESTUARIES.  .  31 

at  13,600  square  miles,  and  the  annual  mud-discharge  at  7,400,000,000 
cubic  feet.  Upon  these  data  he  makes  the  probable  age  of  the  delta 
33,500  years.  To  this  he  adds  half  as  much  for  the  age  of  the  river- 
swamp,  making  in  all  50,000  years. 

It  is  eviden-t,  however,  that  this  estimate  can  not  be  relied  on  as 
even  approximately  accurate.  For  there  is  no  reason  why  the  time  of 
river-swamp  deposit  should  be  added  to  that  of  the  delta,  for  they  were 
both  probably  formed  at  the  same  time — one  by  deposits  higher  up  the 
river,  the  other  by  deposits  at  the  mouth.  Again,  on  the  other  hand, 
the  estimate  takes  no  account  of  the  submarine  extension  of  the  delta, 
in  area  certainly,  and  in  cubic  contents  probably,  much  greater  than 
the  subaerial  delta.  Figs.  22  and  23  are  an  ideal  section  and  a  map  of 
a  delta  in  which  a  is  the  aerial  and  b  the  submarine  portion.  This 
would  greatly  increase  the  time. 

It  is  evident,  therefore,  that  although  the  problem  is  one  of  great 
interest,  we  are  not  yet  in  possession  of  data  to  make  a  reliable  estimate. 
Every  estimate,  however,  indicates  a  very  great  lapse  of  time. 

But  it  must  not  be  imagined,  as  all  estimators  seem  to  do,  that  this 
time,  be  it  greater  or  less  than  Mr.  Lyell's  estimate,  belongs  all  to  the 
present  geological  epoch.  Prof.  Hilgard  has  shown  that  the  true  allu- 
vial deposit  of  the  Mississippi  is  only  fifty  to  one  hundred  feet  thick. 
Beneath  this  the  deposit  belongs  to  the  Quaternary  or  preceding  geo- 
logical epoch. 

7. — Estuaries. 

We  have  already  seen  that  rivers  which  empty  into  iidfijess  seas 
communicate  with  the  sea  by  numerous  branches  traversing  an  alluvial 
flat,  formed  by  the  deposits  of  the  river ;  while  rivers  emptying  into 
tidal  seas  communicate  by  wide  mouths  or  bays,  formed  by  the  erosive 
action  of  the  flowing  and  ebbing  tide.  Such  bays  are  called  estuaries. 
We  have  fine  examples  of  estuaries  in  the  Amazon  and  La  Plata  Rivers, 
in  the  Delaware  and  Chesapeake  Bays,  in  the  friths  of  Scotland  and  the 
fiords  of  Norway ;  in  fact,  at  the  mouths  of  all  the  rivers  emptying  into 
the  Atlantic  on  our  own  coast  as  well  as  on  the  European  coast.  The 
mouth  of  the  Columbia  River  is  a  good  example  on  the  Pacific  coast. 
The  phenomena  of  a  delta  and  an  estuary  are  sometimes  combined  in 
the  same  river.  This  is  the  case  to  some  extent  in  the  Ganges. 

Mode  of  Formation. — Estuaries  are  evidently  formed_b^_ih&  erosive 
action  of  the  inflowing  and  outflowing  tide.  Their  shape,  narrow  above 
ImcTwidemug  toward  the~^ea,~ gives" "great  force  to  the  tidal  current, 
which,  entering  below  and  concentrated  in  the  ever-narrowing  channel, 
rushes  along  with  prodigious  velocity  and  rises  to  an  immense  height. 
In  the  Bay  of  Fundy  the  tide  rises  seventy  feet,  and  at  Bristol,  England, 
it  rises  forty  feet,  in  Puget  Sound  twenty-five  feet.  Sometimes,  from 
obstructions  at  the  mouth  of  the  river,  the  tide  enters  as  one  or  more 


32  AQUEOUS  AGENCIES. 

immense  wavesj  rushing  along  like  an  advancing  cataract.  This  is 
called  an  eagre  or  lore.  The  finest  examples  are  perhaps  in  the  Amazon 
and  Tsien-tang  Rivers.  In  the  eagre  of  the  Amazon  "  the  tide  passes 
up  in  the  form  of  three  great  waves,  thirteen  to  twenty-three  feet 
high."  *  In  the  Tsien-tang,  a  single  wave  plunges  along  at  the  rate  of 
twenty-five  miles  an  hour,f  with  perpendicular  front,  like  an  advancing 
cataract,  four  or  five  miles  wide  and  thirty  feet  high.  In  the  river 
Severn  also  we  have  a  remarkable  example  of  an  eagre.  According  to 
the  laws  already  developed  (pp.  19  and  20),  the  erosive  and  transport- 
ing power  of  such  currents  must  be  immense. 

Deposits  in  Estuaries. — The  larger  portion  of  the  materials  thus 
eroded  is  carried  out  to  sea  by  the  retreating  tide,  and  will  be  again 
spoken  of  under  "  Sea-deposits."  A  portion  of  these  materials,  how- 
ever, is  always  deposited  in  the  estuary  in  sheltered  coves  and  bays 
(Fig.  24,  a  and  Z>),  and  often,  when  the  outflowing  tide  is  obstructed  by 
sand-spits  and  islands  at  the  mouth,  over  every  portion  of  the  estuary. 
In  addition  to  this,  especially  in  rivers'  subject  to  great  freshets,  there 
are  deposits  of  silt  from  the  river.  Thus  many  estuaries  are  occupied 
alternately,  during  the  wet  and  dry  seasons,  by  fresh  and  brackish  or  salt 
water,  and  the  deposits  in  them  are  therefore  alternately  fresh -water 
and  salt-water  deposits,  containing  fresh- water  and  salt  or  brackish 
water  shells.  These  alternations  are  highly  characteristic  of  estuary- 
deposits  in  all  geological  periods ;  in  fact,  of  all  deposits  at  the  mouths 
of  rivers  where  river  and  ocean  agencies  meet. 

8.— Bars. 

Bars  are  invariably  formed  in  accordance  with  the  law  already 
enunciated  as  that  controlling  all  current-deposits,  viz.,  if  the  velocity 
of  a  current  bearing  sediment  be  checked,  the  sediment  is  deposited. 

There  are  two  positions  in  which  bars  are  formed  :  1.  At  the  mouths 
of  rivers ;  and,  2.  At  the  head  of  the  estuaries.  In  the  first  position 


FIG.  24.— An  Estuary. 


*  Branncr,  Science,  1884,  vol.  iv,  p.  488. 

f  American  Journal  of  Science  and  Arts,  1855,  vol.  xx,  p.  305. 


BARS.  33 

(Fig.  24,  d  d)  the  bar  is  formed  by  the  contact  of  the  river-current 
with  the  still  water  of  the  ocean.  It  is  most  marked  in  the  case  of 
"estuaries.  The  outflowing  tide  scours  out  the  estuary,  carrying  with  it 
sediment  partly  brought  down  by  the  river,  and  partly  the  debris  of 
land  eroded  by  the  inflowing  tide.  The  larger  portion  of  this  is  dropped 
as  soon  as  the  tidal  current  comes  in  contact  with  the  open  sea  and  is 
checked  by  it.  They  are  usually  irregularly  crescentic  in  form.  Such 
are  the  bars  at  the  mouths  of  all  harbors.  In  the  second  position  they 
are  found  just  where  the  upward  current  of  the  inflowing  tide  meets 
the  downward  current  of  the  river,  and  makes  still  water.  At  this 
point  we  have  not  only  a  bar,  but  usually  also  an  extensive  marsh 
caused  by  the  daily  overflow  of  the  river.  Through  this  marsh  the 
river  winds  in  a  very  devious  course,  as  is  common  in  all  rivers  whose 
banks  are  alluvial. 

Thus,  then,  in  rivers  like  the  Mississippi,  emptying  into  tideless  seas 
and  forming  deltas,  there  is  but  one  bar,  viz.,  that  at  the  mouth ;  while 
in  rivers  forming  estuaries  there  are  two  bars,  an  outer  and  an  inner. 
This  inner  bar  may  be  many  miles  up  the  river.  In  the  Hudson  River 
the  inner  bar  is  a  hundred  and  forty  miles  up  the  river,  and  only  a  few 
miles  below  Albany.  This  is  really  the  head  of  tide- water  in  this  river.* 

Bars,  being  produced  by  natural  and  constantly-acting  causes,  can 
not  usually  lie  permanently  removed,  though  they  may  be  sometimes 
greatly  improved.  If  they,  are  scraped  away  by  dredging-machines, 
they  are  speedily  reformed  on  the  same  spot.  If  we  cause  the  river 
itself  to  remove  them,  as  has  sometimes  been  done  by  narrowing  the 
channel  and  thus  increasing  the  erosive  power,  we  indeed  remove  the 
bar,  but  it  is  reformed  farther  down-stream  at  a  new  point  of  equi- 
librium. In  some  cases,  however,  bars  have  been  permanently  removed. 
This  has  been  done  for  the  Danube,  and  recently  by  Capt.  Eads  for  the 
Mississippi,  by  the  construction  of  jetties  running  out  to  deep  water. 
These  confine  the  current,  increase  its  velocity,  and  cause  the  river  to 
scour  away  its  bar,  and  thenceforth  to  deposit  its  sediment  in  water  so 
deep  that  it  will  require  centuries  to  build  up  again  from  the  bottom, 
and  re-form  the  bar. 

"We  have  thus  traced  river  agencies  from  their  source  to  the  sea. 
This  brings  us  naturally  to  ocean  agencies. 

*  There  is  another  important  principle  affecting  the  formation  of  bars  in  rivers  empty- 
ing into  seas,  viz.,  the  flocculation  and  consequent  precipitation  of  clay  sediments,  by  salt- 
water (Ililgard). 


34:  AQUEOUS  AGENCIES. 

SECTION  2. — OCEAN. 
Waves  and  Tides. 

Waves. — Waves  produce  no  current,  and  therefore  no  geological 
effect  in  deep  water.  The  erosive  effect  of  this  agent  is  almost  entirely 
confined  to  the  coast-line,  but  at  this  point  is  incessant  and  powerful. 
The  average  force  of  waves  on  the  west  coast  of  Scotland  for  the  sum- 
mer months  is  estimated  by  Stevenson  at  611  pounds  per  square  foot, 
and  for  the  winter  months  at  2,086  pounds  per  square  foot.*  In  violent 
storms  the  force  is  estimated  at  6,000  pounds  per  square  foot,f  and 
fragments  of  rock  of  many  hundred  tons'  weight  are  often  hurled  to  a 
considerable  distance  on  the  land.  These  fragments  hurled  against  the 

shore  are  the  prin- 
cipal agent  of  wave- 
erosion.  The  ra- 
pidity of  the  erosion 
of  a  coast-line  by  the 
action  of  waves  is 
determined  partly 
by  the  softness  and 
partly  by  the  incli- 
nation of  the  strata. 
If  the  strata  turn 
their  faces  to  the 

waves,  particularly  if  inclined  at  a  small  angle,  the  effect  of  the  waves 
is  comparatively  slight  (Fig.  25) ;  but,  if  the  edges  of  the  strata  are  ex- 
posed to  the  waves,  the  erosion  is  much  greater.  For  instance,  if  the 
strata  be  horizontal,  as  in  Fig.  26,  then  the  strata  are  undermined  and 


FIG.  25. 


FIG.  26.— Section  of  an  Exposed  Cliff. 


FIG.  27. 


form  overhanging  table-rocks,  which  from  time  to  time  fall  into  the 
sea ;  if  the  strata  are  vertical  or  highly  inclined  and  their  edges  turned 
to  the  sea,  then  an  exceedingly  irregular  coast-line  is  formed  and  the 
erosion  is  very  rapid,  as  the  f <frce  of  the  waves  is  concentrated  upon  the 
re-entering  angles.  Fig.  27  is  a  map  view  of  a  coast,  in  which  from  a  to 


*  Dana's  Manual,  p.  654. 


f  Herschel's  Physical  Geography,  p.  75. 


WAVES  AND  TIDES. 


35 


FIG.  28. 


£  the  waves  strike  the  edges,  while  from  a  to  c  they  strike  the  faces  of 
the  same  rocky  strata.  The  arrow  shows  the  direction  of  the  dip  of  the 
strata.  The  difference  in  the  form  of  the  coast-line  is  seen  at  a  glance. 

Waves,  cutting  ever  at  the  shore-line  only,  act  like  an  horizontal  saw. 
The  receding  shore-cliif,  therefore,  leaves  behind  it  an  ever-increasing 
subaqueous  platform  which  marks  the  amount  of  recession.  This  is 
shown  in  the  section  (Fig.  28),  in  which  s  is  the  present  shore-line,  I  the 
water-level,  a  ~b  the  platform,  s'  the  original  shore-line,  and  s'  b  c  the 
original  slope  of  bottom.  The  recession  of  the  shore-line  and  the  for- 
mation of  the  shore  platform  have  been  accurately  observed  in  Lake 
Michigan  (Andrews). 
Level  platforms  termi- 
nated by  cliffs,  therefore, 
when  found  inland, 
sometimes  indicate  the 
position  of  old  shore- 
lines. 

Tides.— The  tide  is 

a  wave  of  immense  base,  and  three  or  four  feet  in  height  in  the  open 
ocean,  produced  by  the  attractjve  force  of  the  moon  and  sun  on  the 
waters  of  the  ocean.  The  velocity  of  this  wave  is  very  great,  since  it 
travels  around  the  earth  in  twenty-four  hours.  In  the  open  ocean  it 
produces  very  little  current,  .only  a  slow  transfer  of  the  water  back  and 
forth,  too  slow  to  produce  any  geological  effect ;  *  but  in  shallow  water, 
where  the  progress  of  the  wave  is  impeded,  it  piles  up  in  some  cases 
forty  to  fifty  feet  in  height,  and  givesj-ise  to  currents  of  great  velocity 
and  immense  erosive  power.  By  this  means  bays  and  harbors  are 
formed,  and  straits  and  channels  are  scoured  out  and  deepened.  Tides 
also  act  an  important  part  in  assisting  the  action  of  waves  upon  the 
whole  coast-line.  The  action  of  waves  on  exposed  cliffs  quickly  forms 
accumulations  of  debris  at  their  base,  composed  of  sand,  mud,  shingle, 
or  rocky  fragments  (Fig.  26),  which  receive  first  and  greatly  diminish 
the  shock  of  the  waves  upon  the  cliff.  The  incessant  beating  of  the 
waves  upon  this  debris  reduces  it  to  a  finer  and  finer  condition,  and 
the  retreating  waves  bear  much  of  it  seaward ;  so  that,  even  without 
the  assistance  of  any  other  agent,  the  protection  is  incomplete,  and  the 
erosion  therefore  progresses.  But  if  strong  tidal  currents  run  along  the 
coast,  these  effectually  remove  such  debris  and  leave  the  cliff  exposed 
to  the  direct  action  of  the  waves. 

Examples  of  the  Action  of  Waves  and  Tides.— The  coasts  of  the 
United  States  show  many  examples  of  the  erosive  action  of  waves  and 
tides.  The  form  of  the  whole  New  England  coast  is  largely  determined 


*  Herschel's  Physical  Geography,  p.  64. 


36  AQUEOUS  AGENCIES. 

by  this  cause.  The  softer  parts  are  worn  away  into  harbors  by  the 
waves  and  scoured  out  by  the  tides,  while  the  harder  parts  reach  out 
like  rocky  arms  far  into  the  sea.  Sometimes  only  small  rocky  islands, 
stripped  of  every  vestige  of  earth,  mark  the  position  of  the  former  coast- 
line. Boston  Harbor  and  the  rocky  points  and  islands  in  its  vicinity  are 
good  examples.  The  process  is  still  going  on,  and  its  progress  may  be 
marked  from  year  to  year. 

On  the  Southern  coast  examples  of  a  similar  process  are  not  want- 
ing. At  Cape  May,  for  instance,  the  coast  is  wearing  away  at  a  rate 
of  about  nine  feet  per  annum.  The  more  exposed  portions  about 
Charleston  Harbor,  such  as  Sullivan's  Island,  are  said  to  be  wearing 
away  even  more  rapidly.  As  a  general  fact,  however,  the  low,  sandy,  or 
muddy  shores  of  the  Southern  coasts  are  receiving  accessions  more 
rapidly  than  they  are  wearing ;  while,  on  the  contrary,  the  New  Eng- 
land coast,  as  proved  by  its  rocky  character,  is  losing  much  more  than 
it  gains.  The  shores  of  Lake  Superior  (Fig.  29)  furnish  many  beauti- 


FIG.  29.— Lake  Superior. 

f  til  examples  of  the  action  of  waves — in  this  case,  of  course,  unassisted 
by  tides.  The  general  form  of  the  lake  along  its  south  shore  is  deter- 
mined by  the  varying  hardness  of  the  rock ;  the  two  projecting  promon- 
tories La  Pointe  (a)  and  Keweenaw  Point  (c)  being  composed  of  hard, 
igneous  rocks,  while  the  intervening  bays  1}  and  d  are  softer  sandstone. 
On  the  south  shore,  about  e,  between  La  Pointe  and  Fond  du  Lac  (/), 
the  conditions  of  rapid  erosion  are  beautifully  seen.  The  shores  are 
sandstone  cliffs,  with  nearly  horizontal  strata.  These  have  been  eroded 
beneath  by  the  waves,  in  some  places  for  hundreds  of  feet,  forming 
immense  overhanging  table-rocks,  supported  by  huge  sandstone  pillars 
of  every  conceivable  shape.  Among  these  huge  pillars,  and  along  these 
low  arches  and  gloomy  corridors,  the  waves  dash  with  a  sound  like  thun- 
der. From  time  to  time  these  overhanging  table-rocks,  with  their  load 
of  earth  and  primeval  forests,  fall  into  the  lake. 


WAVES  AND  TIDES.  37 

The  coasts  of  Europe  furnish  examples  on  a  more  magnificent  scale, 
and  have  been  more  carefully  studied.  The  cliffs  of  Norfolk  are  carried 
away  at  a  rate  of  three  feet,  and  those  of  Yorkshire  six  feet,  annually. 
The  church  of  the  Reculvers,  on  the  coast  of  Kent,  near  the  mouth  of 
the  Thames,  stood,  in  the  time  of  Henry  VIII,  one  mile  inland.  Since 
that  time  the  sea  has  steadily  advanced  until,  in  1804,  a  portion  of  the 
churchyard  fell  in,  and  the  church  was  abandoned  as  a  place  of  wor- 
ship. The  church  itself,  ere  this,  would  have  been  undermined  and 
fallen  in,  had  it  not  been  protected  by  artificial  means.  There  are  many 
instances  in  the  German  Ocean  of  islands  which  have  been  entirely 
washed  away  during  the  historic  period. 

The  tidal  currents  through  the  British  and  Irish  Channels,  along  the 
western  coasts  of  Ireland  and  Scotland,  among  the  Orkneys  and  Heb- 
rides, and  especially  along  the  coast  of  Norway,  are  very  powerful. 
Along  this  latter  coast  it  forms  the  celebrated  Maelstrom.  The  erosive 
effects  of  the  sea  are,  therefore,  very  conspicuous.  On  the  south  and 
east  coast  of  England  the  erosion  is  now  progressing  rapidly.  On  the 
west  coast  of  Ireland  and  Scotland  the  waste  is  not  now  so  great,  be- 
cause the  softer  material  is  all  removed,  but  the  configuration  of  the 
coast  shows  the  waste  which  it  has  suffered.  A  glance  at  a  good  map 
of  Ireland  shows  a  deeply-indented  western  coast,  composed  entirely 
of  alternating  rocky  promontories  and  deep  bays.  On  the  western  coast 
of  Scotland,  and  especially  on  the  Orkney,  Shetland,  and  Hebrides  Isl- 
ands, the  wasting  effect  of  the  sea  has  been  still  greater.  Not  only 
have  we  here  the  same  character  of  coast  as  already  described  (as  seen 
in  the  friths  of  Scotland),  but  many  small  islands  have  been  eroded, 
until  only  a  nucleus  of  the  hardest  rock  is  left ;  and  even  these  have 
been  worn  until  they  seem  but  the  ghastly  skeletons  of  once  fertile  isl- 
ands. Figs.  30  and  31  will  give  some  idea  of  the  appearance  of  these 
spectral  islands. 


FIG.  30. 


38 


AQUEOUS  AGENCIES. 


The  coast  of  Norway  consists  entirely  of  deep  fiords  alternating 
with  jutting  headlands  of  hardest  rock  several  thousand  feet  high. 
Along  this  intricately-dissected  coast  there  runs  a  chain  of  high,  rocky 


FIG.  31. 

islands,  which  in  an  accurate  map  is  scarcely  distinguishable  from  the 
coast  itself,  being  separated  only  by  narrow,  deep  fiords.  Toward  the 
northern  part  of  the  coast  the  crest  of  the  Scandinavian  chain  seems  to 
run  directly  along  the  jutting  promontories  of  the  coast-line,  for  these 
headlands  are  the  most  elevated  part  of  the  country ;  in  fact,  in  some 
parts  it  would  seem  that  the  original  crest  was  at  one  time  still  farther 
west,  along  the  line  of  coast-islands.  If  so,  then  the  sea  has  not  only« 
carried  away  the  whole  western  slope,  but  has  broken  through  the  main 
axis,  leaving  only  these  isolated  rocky  islands  as  monuments  of  its 
former  position,  and  is  even  now  carrying  its  ravages  far  inland  on  the 
eastern  slope.  In  the  case  of  Norway,  however,  and  probably  in  case 
of  nearly  all  bold,  rocky  coasts,  the  intricacy  of  the  coast-line  is  not 
due  wholly  or  even  principally  to  the  action  of  waves  and  tides,  but  also 
to  other  causes  to  which  we  shall  refer  hereafter. 

Transporting  Power. — The  transporting  power  of  waves  is  immense- 
ly great,  often  taking  up  and  hurling  on  shore  masses  of  rock  hundreds 
of  tons  in  weight ;  but,  being  entirely  confined  to  the  coast-line,  the  dis- 
tance to  which  they  carry  is  necessarily  very  limited.  There  are  some 
instances,  however,  of  materials  carried  to  great  distances  by  the  inces- 
sant action  of  waves.  Thus,  according  to  Prof.  Bache,  coast-sand  is 
carried  slowly  farther  and  farther  south  by  the  action  of  waves,  and 
siliceous  sand  is  found  at  Cape  Sable  on  the  extreme  southern  point  of 
Florida,  although  the  whole  Florida  coast  as  far  as  St.  Augustine  is 
composed  of  coral  limestone  alone.  He  accounts  for  this  by  supposing 
that  the  trend  of  the  United  States  coast  is  such  that  waves  coming 
from  the  east  strike  the  coast  obliquely  and  fall  off  toward  the  south, 


OCEANIC  CURRENTS.  39 

carrying  each  time  a  little  sand  with  them.  A  similar  phenomenon 
has  been  observed  on  Lake  Michigan ;  the  sands  are  carried  steadily 
toward  the  south  end,  where  they  accumulate. 

Deposits. — The  invariable  effect  of  waves,  chafing  back  and  forth 
upon  coast  debris,  is^  to  wear  off  their  angles  and  thus  to  form  rounded 
fragments  and  granules.  Thus,  peoples, ~shmgle,  and  round-grained 
.sand,  though  produced  by  all  currents,  are  especially  characteristic  of 
wave-action.  Ripple-marks  are  also  characteristic  of  current-action 
in  shallow  water.  They  are,  therefore,  always  formed  on  shore  by  the 
action  of  waves  and  tides.  By  means  of  these  characteristics  of  shore 
deposit,  many  coast-lines  of  previous  geological  epochs  have  been  deter- 
mined. 

We  have  seen  that  waves  usually  destroy  land.  In  many  cases, 
however,  they  also  make  land.  This  is  the  case  whenever  other  agen- 
cies, such  as  river  or  tidal  currents,  drop  sediment  in  shallow  water, 
and  therefore  within  reach  of  wave-action.  We  shall  again  speak  of 
these  under  the  head  of  Land  formed  by  Ocean  Agencies. 

Oceanic  Currents. 

The  ocean,  like  the  atmosphere,  is  in  constant  motion,  not  only  on 
its  surface,  but  throughout  its  whole  mass.  The  general  direction  of 
the  currents  in  the  two  cases  is  also  similar,  but  there  are  disturbing  and 
complicating  causes  peculiar  to  each,  which  interfere  with  the  regularity 
and  simplicity  of  the  phenomena.  If  the  currents  of  the  atmosphere 
are  more  variable  on  account  of  the  greater  levity  of  the  fluid,  oceanic 
currents  have  also  their  peculiar  disturbing  causes  in  the  existence  of 
impassable  barriers  in  the  form  of  continents.  In  both  atmosphere  and 
sea,  currents  may  also  be  deflected  by  submarine  banks,  for  mountain- 
chains  are  the  banks  of  the  aerial  ocean. 

Theory  of  Oceanic  Currents. — By  some  distinguished  physicists, 
oceanic  currents  have  been  attributed  entirely  to  the  action  of  the  trade- 
winds*  There  can  be  no  doubt  that  this  is  a  real  cause;  yet  it  seems 
probable,  nay,  almost  certain,  that  the  great  and  controlling  cause  of 
currents  of  the  ocean,  as  of  the  air,  is  difference  of  temperature  between 
the  equatorial  and  polar  regions,  f  We  will,  therefore,  discuss  the  sub- 
ject from  this  point  of  view,  although  the  effect  would  be  much  the 
same,  whatever  be  our  view  of  the  theory.  For  the  sake  of  clearness, 
we  will  take  first  the  simplest  case,  and  then  introduce  disturbing  in- 
fluences and  show  their  effects. 

Suppose,  first,  the  earth  covered  with  a  universal  ocean,  continually 
heated  at  the  equator,  and  cooling  at  the  poles ;  the  difference  of  den- 

*  Herschel,  Physical  Geography,  p.  13 ;  and  Croll,  Climate  and  Time, 
f  Guyot,  Earth  and  Man,  p.  189. 


4-0  AQUEOUS  AGENCIES. 

sity  of  the  equatorial  and  polar  seas  would  cause  exchange  or  circulation 
between  these  regions  by  means  of  north  and  south  currents  in  all 
longitudes,  the  equatorial  currents  being  superficial  because  warm,  and 
the  polar  currents  deep-seated  because  cold.  It  is  obviously  impossible, 
however,  that  the  principal  exchange  should  be  with  the  pole  itself, 
since  this  is  but  a  point,  but  with  the  northern  regions.  Observation 
shows  that  it  is  between  the  equator  and  the  polar  circle.  In  the  case 
we  are  now  considering,  the  exchange,  being  in  all  longitudes,  would 
be  scarcely,  if  at  all,  perceptible. 

Suppose,  second,  the  earth  be  set  a  rotating :  then  the  currents  pass- 
ing from  either  polar  to  the  equatorial  region  would  be  deflected  more 
and  more  to  the  westward  until,  uniting  at  the  equator,  they  would 
there  form  a  directly  westward  equatorial  current  running  around  the 
earth.  This  westward-moving  water  would  be  constantly  turning  north- 
ward and  southward  in  all  longitudes  as  a  superficial  current,  and  finally 
eastward  about  the  polar  circle,  to  join  again  the  deep-seated  polar  cur- 
rent going  to  the  equator ;  thus  forming  a  series  of  regular  ellipses 
lying  over  each  other  in  strata,  dipping  eastward  and  outcropping 
westward — as  represented  in  Fig.  32.  As  the  north  and  south  currents 
a  a'  and  #  V  would  take  place  in  all  longitudes,  they  would  be  scarcely, 
if  at  all,  perceptible ;  but  the  east  currents  d  d',  and  the  westward 
equatorial  current  c  c,  where  all  these  unite,  would  be  decided. 

In  the  third  place,  introduce  continents  passing  across  the  equator 
from  north  to  south,  forming  impassable  barriers  to  the  east  and 

west  currents  c  c  and  d  d. 
Then  many  of  the  lines  of 
current  a  a  a  would  be 
crowded  against  the  west- 
ern shore  of  the  ocean, 
and  of  the  lines  1)  b  l>  against 
the  eastern  shore,  forming 
in  each  case  by  concentra- 
tion very  decided  currents, 
while  in  mid-ocean  these 

FIG.  32.— The  strong  lines  aaa  show  superficial,  and  the    currents  would  be  still  im- 
dotted  lines  bbb  deep-seated  currents.  . 

perceptible.     Ihusthejoer- 

ceptible  currents  of 'an  ocean  situated  between  continents  would  be  rep- 
resented by  the  figure  (Fig.  33)  taken  from  Dana. 

Besides  the  main  currents  above  mentioned  there  would  be  minor 
exchanges  with  the  pole  itself.*  A  portion  of  the  eastward  current  d 
and  d'  would  turn  north  and  southward,  e  e\  and  circling  around  would 
return  toward  the  equator  as  a  deep-seated  current  under  «,  hugging 

*  Dana's  Manual,  p.  38. 


OCEANIC   CURRENTS. 


41 


the  shore  on  account  of  the  westward  tendency  of  all  currents  moving 
toward  the  equator. 

The  effect  of  the  trade-winds  would  be  to  conspire  with  the  cause 
already  discussed  in  the  formation  of  the  equatorial  current  c  c',  and  by 
the  reflection  of  this  from  continents, 
the  other  currents  spoken  of. 

Application.  —  We  will  now  apply 
these  principles  in  the  explanation  of  the 
currents  of  the  Atlantic  Ocean,  for  these 
are  best  known. 

Currents  coming  from  the  north  and 
south  on  the  African  coast,  and  corre- 
sponding to  b  b'  in  the  diagram  Fig.  33, 
unite  to  form  an  equatorial  current  c  c\ 
which  stretches  across  the  Atlantic  until, 
striking  (Fig.  34)  against  the  coast  of 
South  America,  it  turns  north  and  south, 
a  a'.  The  southern  branch  has  not  been 

accurately    traced.       It    probably    turns    FIG.  33.— Ideal  Diagram,  showing  General 
-,•,-,  ,       7,  ,     .          .  Course  of  Oceanic  Currents. 

gradually  eastward,  rf,  and  forming  a 

grand  circle  in  the  southern  Atlantic  joins  again  the  South  African 

current  b'.     The  northern  branch,  «,  runs  along  the  coast  of  South 


jfffi****^ 
&/ 

(i'O/ 


'   •  -'     '- 


90' 


60 


30 


30° 


60° 


.90 


FIG.  34. — General  Course  of  Currents  of  the  Atlantic. 


42  ,        AQUEOUS  AGENCIES. 

America,  through  the  Caribbean  Sea  and  into  the  Gulf  of  Mexico,  from 
which  emerging  it  runs  with  great  velocity  through  the  narrow  straits 
of  Florida  and  thence  under  the  name  of  the  Gulf  Stream  along  the 
coast  of  North  America,  turning  more  and  more  eastward  in  obedi- 
ence to  the  law  already  mentioned,  until  it  becomes  an  eastward  cur- 
rent, d,  about  50°  to  60°  latitude ;  and  then  stretches  across  to  the  coast 
of  Europe,  and  turns  again  southward  to  join  the  equatorial  current. 
A  portion  of  it,  however,  in  its  eastward  course  turns  northward,  e,  and 
returns  as  a  cold  polar  current  hugging  the  shore  of  North  America  as 
a  cold  wall  to  the  Gulf  Stream,  and  thus  passes  south. 

Geological  Agency  of  Oceanic  Currents.— The  velocity  of  oceanic 
currents  is  generally  small,  although,  in  the  case  of  the  Gulf  Stream,  at 
the  Florida  Straits,  it  reaches  almost  the  velocity  of  a  torrent,  viz., 
three  and  a  half  to  five  miles  per  hour.  The  volume  of  water  carried 
by  them  is  almost  inconceivably  great ;  it  is  estimated  that  the  Gulf 
Stream  alone  carries  many  times  more  water  than  all  the  rivers  of  the 
globe.  According  to  Croll,  it  is  equal  to  a  current  fifty  miles  wide  and 
one  thousand  feet  deep,  running  at  a  rate  of  four  miles  per  hour.  The 
geological  agency  of  these  powerful  currents  in  modifying  the  bottom 
of  the  sea  by  erosion  may  be,  and  by  sedimentary  deposit  must  be, 
very  important,  though  as  yet  comparatively  little  known. 

One  of  the  chief  functions  of  oceanic  currents  is  the  transportation 
and  distribution  over  the  open-sea  bottom  of  sediments  brought  down 
by  the  rivers.  By  far  the  larger  part  of  the  debris  of  the  land  is  cer- 
tainly dropped  near  the  shore,  and  marginal  sea-bottoms  are  everywhere 
the  great  theatres  of  sedimentation ;  but,  without  the  agency  of  marine 
currents,  none  would  reach  open  sea,  all  would  be  dropped  near  shore. 
By  the  agency  of  these,  however,  the  finer  portions  are  carried  and 
widely  distributed  over  certain  portions  of  deep-sea  bottoms.  We 
have  undoubted  evidence  of  this  in  some  cases.  Thus  the  sediments 
brought  down  by  the  Amazon  are  swept  seaward  by  a  strong  tide,  and 
then  taken  by  the  oceanic  current  which  sweeps  along  that  coast,  and 
carried  300  miles  and  deposited  much  of  it  on  the  coast  of  Guiana. 
According  to  Humboldt,  the  same  stream  carries  sediment  from  the 
Caribbean  into  the  Gulf  of  Mexico.*  There  is  little  doubt,  too,  that 
much  of  the  sediments  brought  into  the  Gulf  of  Mexico  by  the  Gulf 
rivers  is  swept  along  by  the  Gulf  Stream,  and  a  part  of  it  deposited  on 
Florida  Point  and  the  Bahama  Banks.  The  surface  transparency  of 
the  Gulf  Stream  is  no  objection  to  this  view,  as  a  little  reflection  will 
show.  LQcean-currents  differ  from  rivers,  in  the  fact  that  the  former 
run  in  perfectly  smooth  beds  of  still  water.  There  are,  therefore,  no 
subordinate  currents  from  side  to  side,  or  up  and  down,  whereby  in  river- 

*Lyell's  Principles  of  Geology. 


OCEANIC  CURRENTS.  43 

currents  the  water  is  thoroughly  mixed  up,  and  the  finer  sediments 
preventing  from  settling.  In  ocean-currents  the  conditions  are  as  favor- 
able for  subsidence  as  in  still  water.  It  is  evident,  therefore,  that  sedi- 
ments carried  by  ocean-currents  must  in  a  little  time  sink  out  of  sight, 
although  from  the  great  depth  of  these  currents  they  may  still  be  car- 
ried to  considerable  distances.  Deep-sea  deposits  have  until  recently 
received  little  attention,  although  they  are  acknowledged  to  be  of  the 
greatest  geological  importance. 

s  Submarine  Banks. — These  are  usually  accumulations  of  material 
dropped  by  currents.  They  an-  formed  under  conditions  similar  to 
those  which  determine  the  formation  of  bars ;  i.  e.(^either  by  the  meet- 
ing of  opposing  sediment-laden  currents  or  else  by  such  a  current  coming 


FIG.  35.— Tides  of  the  German  Ocean.    The  curved  lines  represent  successive  positions  of  the  ad- 
vancing tide. 

in  contact  with  still  water.)  In  fact,  the  outer  bar  is  a  true  submarine 
bank.  The  currents  may  be  either  tidal  or  oceanic  or  river.  Admira- 
ble examples  of  both  those  modes  of  formation  are  found  in  the  Ger- 
man Ocean.  The  tidal  wave  from  the  Atlantic  strikes  the  British  Isles, 
passes  round  in  both  directions,  and  enters  this  ocean  from  the  north 
around  the  north  point  of  Scotland,  and  from  the  south  through  the 


44:  AQUEOUS  AGENCIES. 

British  Channel  and  Straits  of  Dover  (Fig.  35).  These  two  currents 
coming  from  opposite  directions  meet  and  make  still  water,  and  there- 
fore deposit  their  sediment  and  form  banks.  Again,  the  tidal  current 
is  concentrated  in  the  British  Channel,  and  runs  with  great  velocity, 
scouring  out  this  channel,  and  in  addition  gathering  abundant  sediment 
from  the  rivers  emptying  into  the  channel.  Thus  loaded  with  sedi- 
ment it  rushes  through  the  narrow  Straits  of  Dover,  and,  coming  in 
contact  with  the  still  water  of  the  German  Sea,  forms  eddies  on  either 
side,  and  deposits  its  sediments.  Besides  the  banks  thus  formed,  there 
are,  of  course,  bars  formed  at  the  mouths  of  the  rivers  emptying  into 
this  shallow  sea.  By  a  combination  of  all  these  causes,  we  explain  the 
numerous  ban'ks  which  render  the  navigation  of  this  sea  so  dangerous. 
But  great  banks  far  away  from,  shore  are  usually  formed  by  oceanic 
currents.  Thus  the  Banks  of  Newfoundland  are  evidently  formed, 
partly  at  least,  by  the  meeting  of  the  polar  current  (e,  Fig.  34),  bearing 
icebergs  loaded  with  earth,  and  the  warm  current  of  the  Gulf  Stream, 
perhaps  also  bearing  its  share  of  fine  sediment.  Again,  the  Gulf 
Stream,  rushing  at  high  velocity  (four  miles  per  hour)  through  the 
narrow  Straits  of  Florida,  coming  in  contact  with  the  still  water  of 
the  Atlantic  beyond  and  forming  eddies  on  each  side,  and  depositing 
sediment,  has  certainly  contributed  to  form,  if  it  has  not  wholly  formed, 
the  Bahama  Banks  on  one  side,  and  the  bank  on  which  the  Florida 
reefs  are  built  on  the  other.  It  is  probable  that  many  other  peculiari- 
ties of  the  Atlantic  bottom  in  the  course  of  the  Gulf  Stream  may  be 
similarly  accounted  for.* 

Land  formed  by  Ocean  Agencies.—  Upon  submarine  banks,  however 
these  may  be  produced,  are  gradually  formed  islands.  These  islands 
are  always  formed  by  the  immediate  agency  of  waves.  As  soon  as  the 
submarine  bank  rises  so  near  the  surface  that  the  waves  touch  bottom, 
and  form  breakers,  these  commence  to  throw  up  the  sand  or  mud  until 
an  island  is,  formed,  which  continues  to  grow  by  the  same  agency,  until 
it  becomes  inhabited  by  plants  and  animals,  and  finally  by  man.  The 
height  of  such  islands  above  the  sea  will  depend  upon  the  height  of  the 
tides  and  the  force  of  the  waves.  They  are  seldom  more  than  fifteen 
feet  above  high  water.  Thus,  we  find  that  extensive  banks  are  always 
dotted  over  with  islands.  In  this  manner  are  formed  the  low  islands  so 
common  about  the  mouths  of  harbors  and  estuaries,  also  the  narrow 
sand-spits  all  along  our  Southern  coast,  separating  the  harbors  and 
sounds  from  the  ocean.  Fig,  36,  which  is  a  map  of  the  North  Carolina 
coast,  will  give  a  good  idea  of  these  sand-spits.  In  the  course  of  time 
such  sounds,  being  protected  in  some  measure  by  the  sand-spits  from 

*  See  the  author's  views  on  this  subject,  American  Journal  of  Science,  vol.  xxiii,  p, 
45,  1857;  Nature,  vol.  xxii,  p.  558,  1880;  Science,  vol.  ii,  p.  764,  1883. 


GLACIERS. 


the  scouring  action  of  the  tides,  are 
gradually  filled  up  with  sediments 
brought  down  by  the  rivers,  leaving 
only  narrow  passages  for  the  flow  of 
the  tide.  In  this  manner  were 
formed  the  sea-islands  all  along  our 
Southern  coast,  separate~d  from  the 
mainland  only  by  narrow  tidal  in- 
lets. These  tidal  inlets  may  become 
filled  up,  and  the  whole  coast-line 
transferred  farther  seaward. 

A  large  portion  of  the  coasts  of 
the  world  is  thus  bordered  by  wave- 
formed  islands.  We  have  already 
seen,  however,  that  on  some  coasts, 
e.  g.,  Norway,  Scotland,  etc.,  islands 
are  formed  by  the  destructive  ac- 
tion of  waves.  Bordering 'jxlands, 
so  common  along  all  coasts,  are 
therefore  of  two  classes,  and  formed 
by  two  opposite  effects  of  waves — 
the  one  land-destroying,  the  other 
land-forming.  The  islands  of  one 
class  are  high  and  rocky,  of  the  other  low  and  sandy  or  muddy ;  the 
former  are  the  scattered  remains  of  an  old  coast-line,  the  latter  the 
commencing  points  of  a  new  coast-line.* 

SECTION  3. — ICE. 

The  agency  of  ice  will*  be  considered  under  the  heads  of  Glaciers 
and  Icebergs ;  the  effects  of  frost  in  disintegrating  rocks  having  been 
already  treated  of  under  Atmospheric  Agencies.  It  is  only  compara- 
tively recently  that  the  great  importance  of  ice  as  a  geological  agent 
has  been  recognized.  To  Agassiz  is  due  the  credit  of  having  first 
fully  recognized  this  importance. 

Glaciers. 

Definition. — In  many  parts  of  the  earth,  where  the  mountains  reach 
into  the  region  of  perpetual  snow,  and  other  favoring  conditions  are 
present,  we  find  that  the  mountain-valleys  are  occupied  by  masses  of 
compact  ice,  connected  with  the  snow-cap  above,  but  extending  far 
below  the  snow-line  into  the  region  of  cultivated  fields,  and  moving 
slowly  but  constantly  down  the  slope  of  the  valley.  Such  valley-pro- 


Fio.  36. — Coast  of  North  Carolina. 


*  Coast  islands  arc,  however,  often  formed  by  subsidence 


margins. 


46  AQUEOUS  AGENCIES. 

longations  of  the  perpetual  snow^caps  are  called  glaciers.  The  exist- 
ence of  glaciers  and  their  motion  are  necessitated  by  the  great  law  of 
circulation,  so  universal  in  Nature.  For  in  those  countries  where 
glaciers  exist,  the  waste  of  perpetual  snow  by  evaporation  is  small  in 
comparison  with  the  supply  by  the  fall  of  snow.  There  would  be  no 
limit,  therefore,  to  the  accumulation  of  snow  on  mountain-tops,  if  it 
did  not  run  off,  down  the  slope,  by  these  ice-streams,  and  thus  return 
into  the  general  circulation  of  meteoric  waters.  Glaciers  extend  not 
only  far  below  the  snow-line,  but  even  far  below  the  mean  line  of  32°. 
In  the  Alps  the  snow-line  is  about  9,000  *  feet  above  the  sea-level, 
while  some  of  the  glaciers  extend  down  to  within  3,225  feet  (Prest- 
wich)  of  the  same  level,  i.  e.,  more  than  5,000  feet  below  the  snow-line. 

Necessary  Conditions. — The  conditions  necessary  to  the  formation 
of  glaciers  are  :  1.  The  mountain  must  rise  into  the  region  of  perpetual 
snow,  for  the  snow-cap  is  the  fountain  of  glaciers.  2.  There  must  be 
considerable  changes  of  temperature,  and  therefore  alternate  thawings 
and  freezings.  This  condition  seems  necessary  to  the  gradual  compact- 
ing of  snow  into-glacier-ice.  The  want  of  this  condition  is  apparently 
the  cause  of  the  non-existence,  or  small  development,  of  glaciers  in 
tropical  regions.  3.  A  moist  atmosphere  is  favorable  to  their  produc- 
tion, for  the  moister  the  climate  the  greater  is  the  snow-fall,  and  the 
smaller  is  the  waste  by  evaporation,  and  therefore  the  greater  the 
excess  which  must  run  off  by  glaciers.  This  is  an  additional  reason 
why  glaciers  are  not  formed  under  the  equator ;  for  the  great  capacity 
for  moisture  of  the  air  in  this  zone  increases  the  waste  while  it  decreases 
the  fall  of  snow.  This  is  also  the  reason  of  the  scanty  formation  of 
glaciers  in  the  Sierra  Mountains,  and  their  abundance  and  magnitude 
in  the  Alps. 

Ramifications  of  Glaciers. — We  have  said  glaciers  are  valley-prolon- 
gations of  the  ice-cap.  Now,  mountain-valleys  are  of  two  kinds,  viz., 
1.  The  deeper  and  larger  longitudinal  valleys,  between  parallel  ranges ; 
and,  2.  The  transverse  or  radiating  valleys,  transverse  in  case  of  ridges, 
and  radiating  in  case  of  peaks.  The  longitudinal  valleys  may  be  formed 
either  by  erosion  or  by  igneous  agencies  folding  the  crust  of  the  earth  ; 
but  the  transverse  or  radiating  valleys  are  always  formed  by  erosion. 
It  is  these  valleys  of  erosion  which  are  occupied  by  glaciers.  In  coun- 
tries where  there  are  no  glaciers  they  are  occupied,  of  course,  by 
streams.  We  have  already  shown  (p.  9)  how  these  valleys  commence 
near  the  top  of  the  mountain  as  furrows,  which,  uniting,  form  gullies, 
and  these,  in  their  turn,  forming  ravines  and  gorges,  thus  becoming  less 
and  less  numerous,  but  larger  as  we  approach  the  base  of  the  mountain. 
In  the  same  manner,  therefore,  as  streams  ramify,  so  also  do  glaciers. 

*  Dana's  Manual  of  Geology. 


GLACIERS. 


47 


48  AQUEOUS  AGENCIES. 

The  only  difference  is  the  degree  of  ramification.  Streams  ramify 
almost  infinitely,  while  glaciers  seldom  have  more  than  three  or  four 
tributaries.  Fig.  37  is  a  map  of  the  Mont  Blanc  glacier  region.  By 
inspection  of  this  map  it  will  be  seen  that  the  Mer  de  Glace,  m,  receives 
four  tributaries,  marked  t,  ?,  g,  etc.  On  page  55  is  an  enlarged  view 
of  the  same  glacier  with  its  tributaries. 

Motion  of  Glaciers. — Again,  we  have  said  in  our  definition  that  gla- 
ciers are  in  constant  motion.  By  the  law  of  circulation,  constant  down- 
ward motion  is  as  necessary  to  the  idea  of  a  glacier  as  it  is  to  that  of  a 
river,  since  both  the  glacier  and  the  river  carry  away  the  excess  of  sup- 
ply over  evaporation.  But  a  glacier,  though  in  constant  motion,  never 
passes  beyond  a  certain  point,  where  the  slow  downward  motion  is 
exactly  balanced  by  the  melting  of  the  ice  by  sun  and  air.  This  point 
is  called  the  loiver  limit  of  the  glacier.  As  long  as  conditions  remain 
unchanged,  the  lower  end  of  the  glacier  remains  exactly  at  the  same 
point,  although  the  substance  of  the  glacier  moves  always  downward. 
But  if  external  conditions  change,  the  point  of  the  glacier  may  move 
upward  or  downward.  There  are  two  opposing  conditions  which  de- 
termine the  position  of  the  point  of  the  glacier,  viz.,  the  rate  of  mo- 
tion and  the  rate  of  melting.  Thus,  during  a  succession  of  cool,  damp 
years,  the  melting  being  less  rapid,  the  point  of  the  glacier  moves 
slowly  down,  sometimes  invading  cultivated  fields  and  overturning 
huts,  until  it  finds  a  new  point  of  equilibrium.  During  a  succession  of 
warm  and  dry  years,  on  the  contrary,  the  melting  being  more  rapid, 
the  point  retreats,  to  find  a  new  point  of  equilibrium  higher  up  the 
mountain.  Again,  during  a  cycle  of  years  of  heavy  snow-fall,  the  gla- 
cier is  flooded,  its  motion  increased,  and  its  point  advances;  while 
during  a  cycle  of  smaller  snow-fall  its  dimensions  shrink,  its  motion 
is  retarded,  and  its  point  retreats.  But,  whether  the  point  be  station- 
ary, or  advance  or  recede,  the  substance  of  the  glacier  is  ever  moving 
steadily  onward.  It  may  be  compared  to  those  rivers,  in  dry,  sandy 
countries,  which  run  ever  toward  the  sea,  but  never  reach  beyond  a 
certain  point,  being  absorbed  by  the  sand. 

Graphic  Illustration. — These  facts  may  be  graphically  represented 
as  follows  :  Taking  first  the  motion  constant  in  time,  and  the  melting 
variable,  let  a  d  (Fig.  38)  equal  the  length  of  the  mountain-slope, 
and  the  line  a  b  (=  c  d)  the  velocity  of  the  glacier-motion  taken  as 
unifofm.  This  velocity  varies  with  the  slope,  as  will  be  seen  hereafter, 
but  is  little  affected  by  the  elevation.  It  may  be  taken,  therefore,  as 
the  same  in  every  part  of  the  slope,  and  therefore  correctly  represented 
by  equal  lines,  i.  e.,  by  the  ordinates  of  the  parallelogram  a  I  c  d.  The 
melting  power  of  the  sun  and  air,  on  the  contrary,  regularly  increases 
^om  the  top,  where  it  is  almost  nothing,  to  the  bottom  of  the  mount- 
ain. We  will,  therefore,  represent  it  by  the  increasing  ordinates  of  the 


GLACIEES. 


triangle  a  e  d.  At  #,  therefore,  where  the  ordinates  of  the  triangle  and 
of  the  parallelogram  are  equal  to  each  other,  will  be  the  lower  limit  of 
the  glacier.  During  a  succession  of  cool  years 
the  rate  of  melting  will  be  represented  by  the 
ordinates  of  the  smaller  triangle  a  e'  d,  and  the 
point  of  the  glacier  will  advance  to  z.  During 
a  succession  of  warm,  dry  years,  the  rate  of 
melting  will  be  represented  by  the  larger  trian- 
gle a  e"  d,  and  the  point  of  the  glacier  will  re- 
cede to  y.  Taking  next  the  melting  as  con- 
stant in  time,  and  represented  as  before  by  the 
line  a  e,  and  the  motion  as  variable ;  then,  if 
the  rate  of  motion  be  represented  by  ordi- 
nates of  the  line  b  c,  the  point  of  the  glacier 
will  be  at  x  as  before.  But,  during  a  cycle  of 
glacial  flood,  the  rate  of  motion  is  increased  and 
represented  by  a  broken  line  b"  c",  and  the 
point  of  equilibrium  is  advanced  to  z';  and, 
during  a  cycle  of  diminished  snow-fall  and 
shrunken  glacier,  the  rate  of  motion  is  repre- 
sented by  V  c',  and  the  point  of  equilibrium 
retreats  to  y'. 

Of  these  two  factors  of  advance  and  retreat, 
the  second  is  probably  the  greatest ;  for,  in 
the  same  region  and  under  the  same  climatic 
conditions,  some  glaciers  may  be  advancing  and 

some  retreating.  The  reason  is  as  follows :  As  in  small  streams  the 
floods  quickly  follow  the  rain,  while  in  long  rivers  like  the  Mississippi 
the  flood  at  the  mouth  may  be  delayed  a  week  or  ten  days ;  so  in  short 
glaciers  the  ice-flood  may  reach  the  point  in  five  or  ten  years,  while  in 
long  glaciers  it  may  take  fifty  or  more  years.* 

Line  of  the  Lower  Limit  of  Glaciers. — We  have  said,  again,  that  the 
glacier  reaches  below  the  snow-line.  There  are  three  lines,  or  rather 
spheroidal  surfaces,  running  above  the  surface  of  the  earth,  which  are 
apt  to  be  confounded  with  one  another,  and  must,  therefore,  be  now 
defined.  ^These  are  the  line  of  perpetual  snow^  the  mean  line  of  32°, 
and  the  line  of  the  lower  limit  of  glaciers^)  The  line  of  perpetual  snow, 
at  the  equator,  is  about  16,000  to  17,000  feet  above  the  sea-level.  As 
we  approach  the  poles  it  gradually  approaches  the  sea-level,  until  it 
touches  at  or  near  the  poles,  forming  thus  a  spheroid  more  oblate  than 
the  earth  itself  (Fig.  39).  Next  follows  the  mean  line  of  32°.  This 
commences  at  the  equator,  E,  coincident  with  the  snow-line  (it  may 


«•       e    e'    c    c' 

FIG.  38.—  Diagram  showing  the 
Causes  of  Advance  and  Re- 
treat. The  dotted  lines  rep- 
resent increase  and  decrease 
of  melting,  the  broken  lines 
increase  and  decrease  of  mo- 
tion. 


'ft 


*  Forcl,  Archives  des  Sciences,  vol.  vi,  pp.  5,  and  448,  1881. 


50 


AQUEOUS  AGENCIES. 


be  even  above  it — Dana),  but  diverges  as  we  pass  toward  the  pole, 
and  finally  touches  the  sea-level  at  about  66°  north  and  south  latitude, 
at  I  I.  Below  this,  again,  is  the  line  of  lower  limit  of  glaciers,  which, 

commencing  again 
nearly  coincident  with 
the  two  preceding,  at 
the  equator,  approach- 
es and  touches  the  sea- 
level  at  about  50°  lati- 
tude, or,  under  favor- 
able circumstances,  at 
even  lower  latitudes. 
The  difference  be- 
tween these  lines  is 
often  several  thousand 
feet.  In  the  Alps,  the 
line  of  32°  is  2,000  feet, 
and  the  line  o .  lower 
limit  of  glaciers  5,000 
feet,  below  the  snow- 
line.  In  some  parts 
of  the  arctic  region, 
the  line  of  32°  is  3,500 
feet  below  the  snow-line,  and  in  Norway  the  lower  limit  of  glaciers 
is  4,000  feet  below  the  line  of  32°  (Dana).  For  the  sake  of  simplicity 
we  have  represented  the  surfaces,  of  which  these  lines  are  the  sections, 
as  regular  spheroids  ;  but,  in  fact,  they  are  very  irregular,  being  much 
influenced  by  climate.  Their  intersection,  with  the  sea-level  will, 
therefore,  not  be  along  lines  of  latitude,  but  will  be  irregular,  like  iso- 
therms. As  the  line  a  c  marks  the  lower  limit  of  glaciers  in  different 
latitudes,  it  is  evident  that  at  c  glaciers  will  touch  the  sea,  and  beyond 
this  point  will  run  far  into  the  sea.  It  is  in  this  manner,  as  we  will  see 
hereafter,  that  icebergs  are  formed.  In  Chili,  glaciers  touch  the  sea- 
level  at  46°  40'  south  latitude.* 

General  Description. — In  glacial  regions  a  mountain-valley  is  occu- 
pied in  its  highest  part  by  perpetual  snow ;  below  this,  farther  down 
the  valley,  by  neve — a  granular  snow,  intermediate  between  snow  and 
ice ;  still  farther  down,  by  true  glacier- ice ;  and,  finally,  by  a  river  (Fig. 
44).  This  river  is  formed  partly  by  the  melting  of  the  whole  surface 
of  the  glacier,  both  above  and  below,  and  partly  by  the  natural  drain- 
age of  the  valley.  The  glacier,  however,  is  the  principal  source.  From 
the  point  of  every  glacier,  therefore,  runs  a  river. 


FIG.  39.  —General  Relation  of  Limit  of  Glaciers  to  Snow-Line. 


D'Archiac,  Histoire  de  G£ologie. 


GLACIERS.  51 

The  size  of  glaciers  varies  very  much.  Alpine  glaciers  are  some  of 
them  fifteen  miles  long,  and  vary  from  half  a  mile  to  three  miles  in 
breadth,  and  from  one  hundred  to  six  hundred  feet  in  thickness.  In 
the  region  about  Mont  Blanc  and  Finsteraarhorn  alone  there  are  about 
four  hundred  glaciers.  In  the  temperate  regions  of  North  America, 
glaciers  are  found  only  on  the  Pacific  coast,  in  the  Sierra  and  Cascade 
Kanges.  On  Mount  Shasta,  and  especially  on  Mount  Rainier,  glaciers 
equal  to  those  of  the  Alps  have  been  recently  found.  In  the  Himalaya 
Mountains  they  are  developed  upon  a  much  more  gigantic  scale ;  but 
it  is  only  in  arctic  regions  that  we  can  form  any  just  conception  of  their 
immense  importance  as  geological  agents.  In  Spitzbergen  a  glacier 
was  seen  eleven  miles  wide  and  four  hundred  feet  thick  at  the  point.* 
Of  course,  this  thickness  only  represents  the  part  above  water.  By  far 
the  larger  part,  or  six  sevenths,  is  below  water-level.  In  Greenland  the 
great  Humboldt  Glacier  enters  the  sea  with  a  point  forty-five  miles  wide 
and  three  hundred  feet  thick  (Kane).  The  Muir  Glacier,  Alaska,  is 
several  hundred  miles  long.f  But  even  these  examples  give  an  incom- 
plete idea  of  the  whole  truth.  Greenland  is  apparently  entirely  cov- 
ered with  an  immense  sheet  of  ice,  several  thousand  feet  thick,  which 
moves  slowly  seaward,  and  enters  the  ocean  through  immense  fiords.  J 
Judging  from  the  immense  barrier  of  icebergs  found  by  Captain 
Wilkes  (United  States  Exploring  Expedition)  on  its  coast,  the  antarctic 
continent  is  probably  even  more  thickly  covered  with  ice  than  Green- 
land. 

We  are  apt  to  suppose  that  the  surface  of  a  glacier  must  be  smooth. 
This  is,  however,  very  far  from  being  true.  On  the  contrary,  the  ex- 
treme roughness  of  the  ice-surface  renders  the  ascent  along  the  glacier 
extremely  difficult.  This  inequality  of  surface  is  due  partly  to  unequal 
melting  and  partly  to  vrevasses,  or  fissures.  The  unequal  melting  is 
produced  as  follows:  A  stone,  lying  on  the  surface  of  a  glacier,  pro- 
tects the  surface  beneath  from  the  rays  of  the  sun.  Meanwhile  the 
surrounding  ice.  is  melted,  until  finally  the  slab  of  stone  stands  on  a 
column  of  ice  often  several  feet  in  height  (Fig.  40).  A  slab  seen 
by  Forbes  measured  23  feet  long,  17  feet  wide,  and  3£  feet  thick, 
and  rested  on  a  column  13  feet  high.  In  such  cases  the  stone  finally 
falls  off,  leaving  a  sharp  pinnacle,  and  another  column  commences  to 
form  under  the  stone.  In  this  manner  are  formed  what  are  called 
needles.  .When  we  consider  that  there  are  immense  numbers  of  stones 
on  the  glacier-surface,  we  can  easily  see  that  these  needles  will  multi- 
ply indefinitely.  If,  on  the  other  hand,  a  thin  stratum  of  earth  stains 
the  surface  of  the  glacier  in  spots,  these  spots  will  melt  faster  than  the 

*  Dana's  Manual.  f  Mehan,  Am.  Jour.  Sci.,  vol.  xxviii,  p.  74,  1884. 

\  Dr.  Rink,  Archives  dcs  Sciences,  vol.  xxvii,  p.  155. 


AQUEOUS  AGENCIES. 


surrounding  ice,  because  more  absorbent  of  heat,  and  thus  form  deep 
holes. 

An  admirable  illustration  of  extreme  inequality  of  the  surface  of 
ice  is  seen  in  the  case  of  the  small  residual  glacier  still  remaining  on 


FIG.  40.— Ice-Pillars  on  Parker  Creek  Glacier,  California  (after  Russell). 

Mount  Lyell,  Sierra  Nevada.*  On  the  top  of  Mount  Lyell  there  is  an 
immense  amphitheatre  (cirque),  filled  with  snow  and  ice.  In  August 
the  surface  of  this  ice-field  is  set  with  ice-blades,  three  to  four  feet  high 
and  only  two  feet  apart,  as  in  the  section  Fig.  41.  They  are  probably 

formed  as  follows :  In  winter,  when  the 
snow  is  deep  and  light,  it  is  blown  into 
wind-ripples  on  a  large  scale.  These  soon 
become  fixed  by  surface  melting  and  freez- 
ing, and  then  the  greater  action  of  the 
sun  in  the  troughs,  partly  by  the  reverber- 
ation of  heat  and  partly  by  accumulation 
of  dust  there,  causes  these  to  become 
deeper  and  deeper.  It  is  necessary  to  re- 
member that  there  is  little  snow  nor  rain  in  this  region  after  about  the 
first  of  May  until  November. 

Again,  fissures  or  crevasses,  often  of  great  size,  ten  to  twenty  feet 
wide,  one  hundred  feet  deep,  and  sometimes  running  entirely  across  the 
glacier,  are  very  abundant.  As  the  surface  of  the  glacier  is  often  cov- 
ered with  snow,  and  the  fissures  thus  concealed,  they  form  the  most 
dangerous  feature  connected  with  Alpine  travel.  The  law  which  gov- 
erns their  formation  will  be  discussed  hereafter ;  suffice  'it  to  say  that 


FIG.  41. 


See  paper  by  the  writer,  American  Journal  of  Science,  vol.  v,  p.  333,  1873. 


GLACIERS. 


53 


the  great  transverse  fissures  are  formed  by  the  glacier  passing  over  an 
angle  formed  by  a  sudden  change  in  the  slope  of  the  bed.  Streams, 
produced  by  the  melting  of  ice,  running  on  the  surface  of  the  glacier, 
plunge  into  these  fissures  with  a  thundering  noise,  and  hollow  out  im- 
mense wells,  called  moulins,  and  magnificent  ice-caves.  Although  the 
glacier  moves,  the  greaF  crevasses  and  the  wells  with  their  falls  remain 
stationary,  precisely  as  the  position  of  a  rapid  or  breaker  remains  sta- 
tionary, although  the  river  runs  onward  ;  and  for  the  same  reason,  viz., 
that  it  is  reformed  always  on  the  same  spot. 

From  all  these  causes  the  surface  of  a  glacier  is  often  studded  over 
with  conical  masses  and  projecting  points  of  every  conceivable  shape. 
This  is  well  shown  in  the  accompanying  figure  (Fig.  42).  These  in- 


FIG  42.— Inequalities  of  the  Surface  of  a  Glacier  (after  Agassiz). 

equalities  are,  of  course,  the  result  of  differential  melting.  The  whole 
melting  (ablation)  is  much  greater,  even  as  much  as  twenty-five  feet 
in  the  course  of  the  summer.* 

Earth  and  Stones,  etc.— The  surface  of  a  glacier  is,  moreover,  largely 
covered  with  earth  and  stones  gathered  in  its  course  from  the  crumbling 
cliffs  on  either  side.  These  are  often  so  abundant  as  almost  to  cover 
the  surface.  More  usually,  however,  they  are  distributed  in  two  or  more 
rows,  called  moraines.  Fig.  43  is  a  view  of  a  glacier,  with  its  moraines 
and  lateral  crevasses. 

Such  is  a  general  description  of  the  appearance  of  a  glacier.  There 
are,  however,  several  points  which,  by  their  importance  and  interest, 

*  Prestwich,  Geology,  vol.  i,  p.  176. 


54  AQUEOUS  AGENCIES. 

require  special  notice.     These  are  :  1.  Moraines  ;  2.  Glaciers  as  a  geo- 
logical agent ;  3.   Glacier -motion  ;  and,  4.   Glacier-structure. 


FIG.  43.— Zennatt  Glacier  (Agassiz). 

Moraines. 

/ 

There  are  four  kinds  of  moraines  described  by  writers,  viz.,  lateral 
moraines,  medial  moraines,  terminal  moraines,  and  ground  moraines. 
Lateral  moraines  are  continuous  lines  of  earth  and  stones,  arranged  • 
on  either  margin  of  the  glacier  and  evidently  formed  from  the  ruins  of 
the  crumbling  cliffs  of  the  inclosing  valley.  This  debris  does  not  fall 
from  every  part  of  the  valley-sides,  but  generally  only  from  certain 
bold,  projecting  cliffs.  It  is  converted  into  a  continuous  line  by 
the  motion  of  the  glacier,  just  as  light  materials  thrown  constantly 
into  a  river  at  one  point  would  appear  as  a  continuous  line  on  the 
stream. 

Medial  moraines  are  similar  lines  of  debris,  occupying  the  central 
portions  of  the  glacier.  Sometimes  there  is  but  one ;  sometimes  two,  or 
more ;  sometimes  the  whole  surface  of  the  glacier  is  almost  covered  with 
them.  The  true  explanation  was  first  pointed  out  by  Agassiz.  They 
are  formed  by  the  coalescence  of  the  interior  lateral  moraines  of  tribu- 
tary glaciers,  carried  down  the  main  trunk  by  the  motion  of  the  ice- 
current.  The  accompanying  map  (Fig.  44)  of  the  Mer  de  Glace  and 


f 


MORAINES. 


55 


its  tributaries  shows  clearly  the  manner  in  which  these  moraines  are 

formed.     Both  lateral  and  medial  moraines  are  generally  situated  on  a 

ridge  of  ice,  sometimes  fifty  to  eighty  feet  high,  evidently  formed  by 

the  protection  of  the  ice,  in  this 

part,  from  the  melting  power  of 

the  sun.     The  fragments  of  rock 

brought  down   by  glaciers   are 

often   of   enormous   size.      One 

described  by  Forbes  contained 

244,000  cubic  feet. 

The  ground  moraine  is  the 
mass  of  debris  carried  between 
the  glacier  and  its  bed.  It  is 
derived  partly  from  erosion  of 
the  bed,  and  partly  from  top  ma- 
terial (lateral  and  medial  mo- 
raines) ingulfed  and  carried 
down  to  the  bottom. 

Everything  which  falls  upon 
the  surface  of  the  glacier  is  slow- 
ly and  silently  carried  downward 
by  this  ice-stream,  and  finally 
dropped  at  its  point.  Much 
finely- triturated  matter  is  also 
pushed  along  beneath  the  gla- 
cier, and  finds  its  way  to  the 
same  point.  In  the  course  of 
time  an  immense  accumulation 
is  formed,  of  somewhat  cres- 
centic  shape,  as  seen  in  Fig.  44. 

This  accumulation  is  called  the  terminal  moraine.  It  is  the  delta 
of  this  ice-river.  The  existence  of  moraines  is  a  constant  witness  of 
the  motion  of  the  glaciers. 

Glaciers  as  a  Geological  Agent. 

Glaciers,  like  rivers,  erode  the  surface  over  which  they  move,  carry 
the  materials  gathered  in  their  course  often  to  great  distances,  and 
finally  deposit  them.  In  all  these  respects,  however,  the  effects  of  their 
action  are  perfectly  characteristic. 

Erosion. — When  we  consider  the  weight  of  glaciers  and  their  un~ 
yielding  nature  as  compared  with  water,  it  is  easy  to  see  that  their 
erosive  power  must  be  very  great.  This  is  increased  immensely  by 
fragments  of  stone  of  every  conceivable  size  carried  along  between  the 
glacier  and  its  bed.  These  partly  fall  in  at  the  sides  and  become 


FIG.  44.— Mer  de  Glace. 


56 


AQUEOUS  AGENCIES. 


jammed  between  the  glacier  and  the  confining  rocks,  partly  fall  into 
crevasses  and  work  their  way  to  the  bed,  and  partly  are  torn  from  the 
rocky  bed  itself.  But  on  the  other  hand,  on  account  of  their  slow  mo- 
tion, glacier-erosion  is  by  force  of  pressure,  while  that  of  water  is  by 
force  of  impact.  The  effects  of  glacier- erosion  differ  entirely  from 
those  of  water  :  1.  Water,  by  virtue  of  its  perfect  fluidity,  wears  away 
the  softer  spots  of  rock,  and  leaves  the  harder  standing  in  relief ;  while 
a  glacier,  like  an  unyielding  rubber,  grinds  both  hard  and  soft  to  one 
level.  This,  however,  is  not  so  absolutely  true  of  glaciers  as  might  be 
supposed.  Glaciers,  for  reasons  to  be  discussed  hereafter,  conform  to 
large  and  gentle  inequalities  of  their  beds,  though  not  to  small  ones, 
acting  thus  like  a  very  stiffly  viscous  body.  Thus  their  beds  are  worn 
into  very  remarkable  and  characteristic  smooth  and  rounded  depressions 
and  elevations  called  roches  moutonnees  (Fig.  45).  Sometimes  large 


FIG.  45.— Koches  Moutonnees  of  an  Ancient  Glacier,  Colorado  (after  Hayden). 


and  deep  hollows  are  swept  out  by  a  glacier  at  some  point  where  the 
rock  is  softer  or  where  the  slope  of  the  bed  changes  suddenly  from  a 
greater  to  a  less  angle.  If  the  glacier  should  subsequently  retire,  water 
accumulates  in  these  excavations  and  forms  lakelets.  Such  lakelets  are 
common  in  old  glacial  beds. 

2.  The  lines  produced  by  water- erosion,  if  detectible  at  all,  are 
always  more  or  less  irregular  and  meandering ;  while  those  produced  by 
glaciers  are  straight  and  parallel  (Fig.  46). 

Thus,  smooth,  gently-billowy  surfaces,  marked  with  straight,  parallel 


GLACIERS  AS  A  GEOLOGICAL  AGEXT. 


57 


scratches,  are  very  characteristic  of  glacial  action.  We  will  call  such 
surfaces  glaciated,  and  the  process  glaciation. 

3.  The  turbidity  of  ordinary  rivers  is  usually  yellowish,  the  turbidity 
of  glacial  rivers  is  always  milky.  The  one  is  due  to  sediments  derived 
from  soil,  and  therefore  oxidized ;  the  other  is  due  to  ground-up  sound 
rock  or  rock-meal. 

Transportation. — The  transporting  power  of  glaciers  follows  no  law 
similar  to  that  pointed  out  under  rivers — in  fact,  it  has  no  relation  at 
all  to  velocity.  The  reason  is,  that  the  stone  rests  on  the  surface  as  a 
floating  body.  There  is,  therefore,  no  limit  to  the  transporting  power. 
Bowlders  of  250,000  cubic  feet  are  carried  with  the  same  ease  and  the 
same  velocity  as  the  finest  dust. 

Deposit — Balanced  Stones. — A  water-current  carrying  stones  bruises 
and  rounds  their  corners,  and  deposits  them  always  in  the  most  secure 
positions ;  but  glaciers  often  deposit  huge  angular  fragments  of  rock 
in  the  most  insecure  positions — so  nicely  balanced,  sometimes,  that  a 
touch  of  the  hand  will  dislodge  them.  The  reason  is,  they  are  set 


FIG.  46.— Glacial  Scorings  (after  Agassiz). 

down  by  the  gradually  melting  ice  with  inconceivable  gentleness.  Thus 
balanced  stones,  rocking-stones,  etc.,  are  common  in  glacial  regions. 
In  using  these  as  a  sign  of  glacial  action,  however,  we  must  recollect 
that  a  bowlder  dropped  by  any  agent,  or  even  a  bowlder  of  disintegra- 
tion (p.  6),  may  in  time  become  a  rocking-stone,  by  slow  but  irregular 
disintegration  changing  the  position  of  the  center  of  gravity.  But  angu- 
lar erratics  in  insecure  positions  are  very  characteristic  of  glacial  action. 
Material  of  the  Terminal  Moraine. — The  material  of  the  terminal 
moraine  is  very  characteristic  :  1.  It  consists  of  fragments  of  every  con- 


58 


AQUEOUS  AGENCIES. 


ceivable  size,  from  huge  bowlders  down  to  fine  earth,  mixed  together 
into  an  heterogeneous  mass  entirely  different  from  the  neatly-sorted  de- 
posits from  water.  It  is,  therefore,  entirely  unsorted  and  unstratified, 
and  without  organic  remains.  2.  The  mass  consists  of  two  parts,  viz., 
that  which  was  carried  on  the  top  of  the  glacier,  and  that  which  was 
forced  out  beneath  (ground  moraine).  The  first  consists  of  loose  ma- 
terial containing  angular,  unworn  fragments ;  the  other  of  fine  compact 
material  containing  fragments  worn  and  polished,  and  scratched  with 
straight,  parallel  scratches,  but  in  both  cases  entirely  different  from 
water-worn  pebbles.  In  all  respects,  therefore,  the  action  of  glaciers  is 
characteristic  and  can  not  be  confounded  with  that  of  water. 

Evidences  of  Former  Extension  of  Glaciers.— It  is  by  evidence  of 
this  kind  that  the  former  great  extension  of  glaciers  in  regions  where 

they  now  exist,  and  the  former 
existence  of  glaciers  in  regions 
where  they  no  longer  exist,  have 
been  proved.  We  have  already 
stated  that  during  a  succession 
of  cool,  damp  seasons,  a  glacier 
may  extend  far  beyond  its  pre- 
vious limits.  Similar  changes 
take  place  also  in  the  depth  of 
a  glacier.  In  a  word,  glaciers 

are  subject  to  floods  like  rivers ;  only  these  floods,  instead  of  being  an- 
nual, are  secular.  Now,  as  rivers  after  floods  leave  floating  material 
stranded  on  the  banks,  showing  the  height  of  the  flood - 
water,  so,  in  the  decrease  of  a  glacier,  lines  of  bowlders 
are  left  stranded,  often  delicately  balanced,  on  ledges 
high  up  the  sides  of  the  valley.  These  lines  of  bowl- 
ders mark  the  former  height  of  the  glacier.  Some  of 
these  lines  have  been  found  in  the  Alps  2,000  feet  above 
the  present  level.  Fig.  47  is  a  cross-section  of  a  glacial 
valley.  The  dotted  lines  show  the  former  level.  In 
the  same  valleys  we  find  old  terminal  moraines  (Fig. 
48,  a)  miles  beyond  the  present  limit  of  the  glacier. 
The  characteristic  planing,  polishing,  and  parallel  scor- 
ing, have  been  found  equally  far  above  the  present  level 
and  beyond  the  present  limit  of  Alpine  glaciers. 

Glacial  Lakes. — When  a  glacier  retreats,  the  water 
of  the  river  which  flows  from  its  point  may  accumulate 
in  great  rock-lasins  scooped  out  by  the  glacier,  or  else 
behind  the  old  terminal  moraines.  In  these  two  ways 
lakes  are  often  formed. 


FIG.  47.— Section  across  Glacial  Valley,  showing  old 
Lateral  Moraines. 


-v'.\ 


MOTION   OF  GLACIERS  AND   ITS   LAWS.  59 


Motion  of  Glaciers  and  its  Laws. 

Evidences  of  Motion. — That  glaciers  move  slowly  down  their  valleys 
was  long  known  to  Alpine  hunters.  Rude  experiments  of  the  first  scien- 
tific explorers  confirmed  this  popular  notion.  Hugi  in  1827  built  a  hut 
upon  the  Aar  glacier.  This  hut  was  visited  from  year  to  year  by  scien- 
tific explorers  and  its  change  of  position  measured.  In  1841  Agassiz 
found  that  it  had  moved  1,428  metres  in  fourteen  years,  or  about  100 
metres  (330  feet)  per  annum.  The  ruins  of  Agassiz's  hut  (Hotel 
Neuchatalois),  built  in  1840,  were  found  in  1884.  They  had  moved  in 
forty-four  years  7,900  feet.*  Numerous  other  observations  from  year  to 
year  by  Agassiz  and  others,  on  the  position  of  conspicuous  bowlders  ly- 
ing on  the  surface  of  glaciers,  confirmed  these  results  and  placed  the  fact 
of  glacier-motion  beyond  doubt.  But  the  most  important  observations 
determining  both  the  rate  and  the  laws  of  glacier-motion  were  made 
in  1842  by  Prof  Agassiz  on  the  Aar  glacier,  and  Prof.  Forbes  on  the 
Mer  de  Glace.  By  these  experiments,  carefully  made  by  driving  stakes 
into  the  glacier,  in  a  straight  row  from  one  side  to  the  other,  and  ob- 
serving the  change  in  the  relative  position  of  the  stakes,  it  was  deter- 
mined that  the  center  of  the  glacier  moved  faster  than  the  margins. 
This  differential  motion  is  the  capital  discovery  in  relation  to  the  mo- 
tion of  glaciers.  It  is  claimed  by  both  Agassiz  and  Forbes.  It  had, 
however,  been  previously  distinctly  stated,  though  not  proved,  by  Bishop 
Rendu. 

Laws  of  Glacier-Motion. — The  term  differential  motion  is  a  con- 
densed expression  for  all  the  laws  of  glacier-motion.  It  asserts  that 
the  different  parts  of  a  glacier  do  not  move  together  as  a  solid,  but 
move  among  themselves  in  the  manner  of  a  fluid.  A  glacier  moves 
like  a  fluid,  though  a  very  stiff,  viscous  fluid ;  its  motion  may  therefore 
be  rightly  called  viscoid.  We  will  mention  some 
of  the  most  important  laws  of  fluid  motion,  and 
show  that  glaciers  conform  to  them  : 

1.  TJie  Velocity  of  the  Central  Parts  is  greater 
than  that  of  the  Margins. — This  well-known  law 
of  currents,  the  result  of  friction  of  the  fluid 
against  the  containing  banks,  was  completely  proved 
in  the  case  of  glaciers  by  the  experiments  of  Agas- 
siz and  Forbes,  and  recently  confirmed  in  the  most 
perfect  manner  by  Tyndall.  A  line  of  stakes,  '  Fie.  49. 

a  b  c  d  efg,  placed  in  a  straight  row  across  a  gla- 
cier, becomes  every  day  more  and  more  curved,  as  seen  in  Fig.  49. 
The  exact  rate  of   motion  for   each  stake  is  easily  measured  by  the 


e 

.  c---o  •- 


/ 


*  Nature,  vol.  xxx,  p.  477,  1884. 


60  AQUEOUS  AGENCIES. 

theodolite.  The  rate  of  the  center  is  often  many  times  greater  than 
that  of  the  margins. 

2.  The  Velocity  of  the  Surface  is  greater  than  that  of  the  Bottom. 
—This  law  of  currents,  which  is  the  necessary  result  of  friction  on  the 

bed,  is  more  difficult  to  prove  in  the  case  of  glaciers,  because  it  is  dif- 
ficult to  get  a  vertical  section.  The  necessary  observation  was,  how- 
ever, successfully  accomplished  by  Prof.  Tyndall  in  1857.  We  have 
already  said  (page  56)  that  glaciers  conform  to  large  but  not  to  small 
inequalities  of  their  channels :  a  glacier,  therefore,  passing  by  a  narrow 

side -ravine  will  expose  its  whole 
thickness  on  the  side.  Prof.  Tyn- 
dall, having  found  such  a  side  ex- 
posure more  than  140  feet  vertical, 
placed  three  pegs  in  a  vertical  line, 
one  near  the  top,  one  near  the  mid- 
FIQ  5Q  ""  die  and  one  at  the  bottom  (Fig.  50, 

a  b  c).      The  vertical   line   became 

more  and  more  inclined  daily.  The  daily  motion  at  top  was  six  inches, 
in  the  middle  4*5  inches,  and  at  the  bottom  2'5  inches.  Thus,  glaciers, 
like  rivers,  slide  on  their  beds  and  banks,  producing  erosion ;  but,  also, 
the  several  layers,  both  horizontal  and  vertical,  slide  on  each  other. 

3.  The  Velocity  increases  with  the  Slope. — Fig.  51  represents  the 
surface-slope  of  the  glacier  Du  Geant,  G  ;  the  Mer  de  Glace,  M ;  and 
the  glacier  De  Bois,  B  ;  and  their  daily  motion.     The  increase  of  ve- 
locity with  the  slope  is  evident. 

4.  The  Velocity  increases  with  the  Fluidity. — The  daily  motion  of 
glaciers  is  greater  in  summer,  when  the  ice  is  rapidly  melting,  than  in 
winter ;  and  in  mid-day  than  at  night. 

G 

18  IN  M_ 

5° 
12  ° 

FIG.  51. 

5.  Tlie  Velocity  increases  with  the  Depth. — In  the  Alps,  where  the 
thickness  is  200  to  300  feet,  the  mean  daily  motion  is  one  to  three 
feet ;  but  in  Greenland,  where  the  thickness  is  2,000  to  3,000  feet,  the 
daily  motion,  in  spite  of  the  much  lower  temperature,  is  in  some  cases 
60  feet*  or  even  99  feet.f     The  Muir  glacier  in  Alaska  moves  70  feet 
a  day  (Wright). 

6.  Fluid  Currents  conform  to  the  Irregularities  of  their  Channel. — 
Glaciers,  like  water-currents,  conform  to  the  inequalities  of  the  bottom 

*  Holland,  Journal  of  Geological  Society,  vol.  xxxiii,  p.  142  et  seq. 
f  Science,  vol.  xi,  p.  259,  1888. 


VISCOSITY   THEORY   OF   FORBES. 


61 


FIG.  52. 


and  sides  of  their  channels.     They  have  their  shallows  and  their  deeps, 

their  narrows  and  their  lakes,  their  cascades,  their  rapids,  and  their 

tranquil  portions.     Fig.  52  shows  a  glacier 

running  through  a  narrow  gorge   into  a 

wide  lake  of  ice,  and  again  through  another 

gorge.     There  is  this  difference,  however, 

between  a  glacier  and  a  water-current,  viz., 
that,  while  the  latter 
conforms  to  even  the 
minutest  and  sharpest 
outlines,  the  former  con- 
forms only  to  the  larger 
or  more  gentle.  In  this, 
a  glacier  acts  like  a  stiff, 
viscous  fluid. 

7.  The  Line  of  Swiftest  Motion  is  more  sinuous 
than  the  Channel. — We  have  already  seen  that  this  is 
true  of  rivers  (page  24).  The  line  of  swiftest  current 
is  reflected  from  side  to  side,  increasing  the  curves  by 
erosion.  The  same  has  been  recently  proved  by  Tyn- 
dall  to  be  the  case  with  glaciers.  Fig.  53  represents 
a  portion  of  a  sinuous  glacier,  like  the  Mer  de  Glace : 
FIG.  53.  the  dotted  line  represents  the  line  of  swiftest  motion. 

Theories  of  Glacier  Motion. 

There  are  few  subjects  connected  with  the  physics  of  the  earth 
which  have  excited  more  interest  than  that  of  glacier-motion.  The 
subject  is  one  of  exceeding  beauty,  and  not  without  geological  im- 
portance. Passing  over  several  very  ingenious  theories  which  have 
now  been  abandoned,  the  first  theory  which  was  conceived  in  the  true 
inductive  spirit,  and  which  explains  the  differential  motion,  is  that  of 
Prof.  James  Forbes. 

Viscosity  Tlieory  of  Forbes. 

Statement  of  the  Theory. — According  to  Forbes,  ice,  though  appar- 
ently so  hard  and  solid,  is  really,  to  a  slight  extent,  a  viscous  body.  In 
small  masses  this  property  is  not  noticeable,  but  in  large  masses  and 
under  long-continued  pressure  it  slowly  yields,  and  will  flow  like  a  stiffly 
viscous  fluid.  In  large  masses  like  a  glacier,  this  steady,  powerful  press- 
ure is  furnished  by  the  immense  weight  of  the  superincumbent  ice. 

Argument. — It  is  evident  that  this  theory  completely  accounts  for 
all  the  phenomena  of  glacier- motion,  even  in  their  minutest  details. 
A  glacier,  beyond  all  doubt,  moves  like  a  viscous  body,  but  it  is  still  a 
question  whether  it  does  so  by  virtue  of  a  property  of  viscosity.  The 


(32  AQUEOUS  AGENCIES. 

proposition  that  ice  is  a  viscous  substance  seems  at  first  palpably  ab- 
surd. It  is  necessary,  therefore,  to  show  that  this  proposition  is  not  so 
absurd  as  it  seems. 

The  properties  of  solidity  and  liquidity,  though  perfectly  distinct 
and  even  incompatible  in  our  minds,  nevertheless,  in  Nature,  shade  into 
one  another  in  the  most  imperceptible  manner.  Malleability, plasticity, 
and  viscosity,  are  intermediate  terms  of  a  connecting  series.  The  idea 
which  underlies  all  these  expressions  is  that  of  capacity  of  motion  of 
the  molecules  among  themselves  without  rupture  :  the  difference  among 
them  being  the  greater  or  less  resistance  to  that  motion.  In  the  case 
of  malleable  bodies,  like  the  metals,  great  force  is  required  to  produce 
motion ;  in  plastic  bodies,  like  wax  or  clay,  less  force  is  required ;  in 
viscous  bodies,  like  stiff  tar,  motion  takes  place  spontaneously  but 
slowly ;  while  in  liquids  it  takes  place  freely  and  with  little  or  no  resist- 
ance. In  all  these  cases,  if  the  pressure  be  sufficient,  the  body  will 
change  its  form  without  rupture — in  other  words,  will  floiv.  Now,  by 
increasing  the  mass  we  may  increase  the  pressure  to  any  extent. 
Therefore,  all  malleable,  ductile,  plastic,  or  viscous  bodies,  if  in  suffi- 
ciently large  masses,  will  flow  like  water.  Thus,  a  mass  of  lead,  suffi- 
ciently thick,  would  certainly  flow  under  the  pressure  of  its  own  weight. 

But  solid  bodies  may  be  divided  into  two  great  classes,  viz.,  bodies 
which  are  malleable,  plastic,  or  viscous,  and  bodies  which  are  brittle ; 
the  very  idea  of  brittleness  being  that  of  total  incapacity  of  motion 
among  the  particles  without  rupture.  Now,  ice  belongs  to  the  class  of 
brittle  bodies.  Forbes  attempts  to  remove  this  difficulty  by  showing 
that  many  apparently  brittle  bodies  will  also  flow  under  their  own 
weight ;  for  instance,  pitch,  so  hard  and  brittle  that  it  flies  to  pieces 
under  a  blow  of  the  hammer,  will,  if  the  containing  barrel  be  removed, 
flow  and  spread  itself  in  every  direction.  So,  also,  molasses-candy, 
made  quite  hard  and  brittle,  will  still  flow  by  standing.  A  remarkable 
pitch-lake,  about  three  miles  in  circumference,  occurs  in  Trinidad. 
The  pitch  is  described  as  in  constant,  slow-boiling  motion,  coming  up 
in  the  center,  flowing  over  to  the  circumference,  and  again  sinking 
down.  Yet  this  pitch,  in  small  masses,  would  be  called  solid  and 
brittle.  Struck  with  a  hammer,  it  flies  to  pieces  like  glass.  In  fact, 
the  essential  peculiarity  of  a  stiff,  viscous  body,  in  which  it  differs 
from  malleable  or  plastic  bodies,  is,  that  it  yields  only  to  slowly -applied 
force. 

Forbes,  therefore,  thinks  that  glacier-ice  is  an  exceedingly  stiff,  vis- 
cous substance,  which,  though  apparently  brittle  in  small  quantities  and 
to  sudden  force,  yet,  under  the  slow-acting  but  powerful  pressure  of 
its  own  weight,  flows  down  the  slope  of  its  bed,  squeezing  through 
narrows  and  spreading  out  into  lakes,  conforming  to  all  the  larger  and 
gentler  inequalities  of  bed  and  banks,  but  not  to  the  sharper  ones. 


REGELATION   THEORY   OF  TYNDALL. 


63 


The  velocity  of  motion  is  small  in  the  same  proportion  as  the  viscous 
mass  is  stiff.  The  descent  of  the  Mer  de  Glace  from  the  cascade  of  the 
Glacier  du  Geant  to  the  point  of  Glacier  de  Bois,  a  distance  of  ten  miles, 
is  4,000  feet.  Water,  under  these  circumstances,  would  rush  with  fear- 
ful velocity.  The  glacier  moves  but  two  feet  in  twenty-four  hours. 

Such  viscosity  of  ice  as  supposed  by  Forbes  is  now  proved  by  ex- 
periments. Ice-boards  supported  at  the  two  ends  bend  into  an  arc 
under  their  own  weight.  Cylinders  of  snow  compacted  into  ice  may 
be  bent  in  the  hand  to  a  semicircle  without  rupture,*  and  bars  of  ice 
may  even  be  stretched  by  slow  pulling,  f 

Regelation  Theory  of  Tyndall. 

If  ice  be  indeed  a  viscous  body,  then  there  seems  no  reason  why  it 
should  not  yield  to  pressure  even  in  small  masses,  if  the  pressure  be 
sufficiently  slowly  graduated.  In  the  hands  of  a  skillful  experiment- 
alist it  ought  to  exhibit  this  property.  Prof.  Tyndall  tried  the  ex- 
periment. Masses  of  ice  of  various  forms  were  subjected  to  slowly- 
graduated,  hydrostatic  pressure.  In  every  case,  however  slowly  grad- 
uated the  pressure,  the  ice  broke ;  but  if  the  broken  fragments  were 
pressed  together,  they  reunited  into  new  forms.  In  this  manner,  ice  in 
the  hands  of  Prof.  Tyndall  proved  as  plastic  as  clay :  spheres  of  ice 
(«,  Fig.  54)  were  flattened  into  lenses  ( £),  hemispheres  (c)  were  changed 


FIG.  54.—  A  B  C,  molds;  ace,  original  forms  of  the  ice;  b  df,  the  forms  into  which  they 

were  molded. 

into  bowls  (d),  and  bars  (e)  into  semi-rings  (/).  He  even  asserts  that 
ice  may  be  molded  into  any  desirable  form ;  e.  g.,  into  vases,  statuettes, 
rings,  coils,  knots,  etc.  Here,  then,  we  have  a  power  of  being  molded 
such  as  was  not  dreamed  of  before ;  but  this  power  was  not  depend- 
ent on  a  property  of  viscosity,  but  upon  another  property  long  known, 
but  only  recently  investigated  by  Faraday,  viz.,  the  property  of  re-ge- 
lation. 

*  Aitkin,  American  Journal  of  Science,  vol.  v,  p.  305,  third  series,  1873. 
f  American  Journal  of  Science,  vol.  xxxiv,  p.  149,  1887;  and  Nature,  vol.  xxxix,  p. 
203,  1888. 


61  AQUEOUS  AGENCIES. 

Regelation. — If  two  slabs  of  ice  be  laid  one  atop  of  the  other,  they 
soon  freeze  into  a  solid  mass.  This  will  take  place  not  only  in  cold 
weather,  but  in  midsummer,  or  even  if  boiling  water  be  thrown  over 
the  slabs.  If  a  mass  of  ice  be  broken  to  pieces,  and  the  fragments  be 
pressed  or  even  brought  in  contact  with  one  another,  they  will  quickly 
unite  into  a  solid  mass.  Snow  pressed  in  the  warm  hand,  though  con- 
stantly melting,  gradually  becomes  compacted  into  solid  ice.  This  very 
remarkable  but  imperfectly  understood  property  of  ice  completely  ex- 
plains the  phenomena  of  molding  ice  by  experiment.  By  this  property 
the  broken  fragments  reunite  in  a  new  form  as  solid  as  before.  We 
may  possibly  call  this  property  of  molding  under  pressure  plasticity 
(although  it  is  not  true  plasticity,  since  it  does  not  mold  without  rupt- 
ure, but  by  rupture  and  reyelation) ;  but  it  can  not  in  any  sense  be  called 
viscosity,  for  the  true  definition  of  viscosity  is  the  property  of  yielding 
under  tension  —  the  property  of  stretching  like  molasses-candy,  or 
melted  glass ;  but  ice  in  the  experiments,  according  to  Tyndall,  did  not 
yield  in  the  slightest  degree  to  tension.  In  the  experiment,  if,  instead 
of  placing  the  straight  bar  at  once  into  the  curved  mold,  it  had 
been  placed  successively  in  a  thousand  molds,  with  gradually-increased 
curvature,  or,  still  better,  if  placed  in  a  straight  mold,  and  this  mold, 
while  under  pressure,  curved  slowly,  then  there  would  have  been  no 
sudden  visible  ruptures,  bnt  an  infinite  number  of  small  ruptures  and 
regelations  going  on  all  the  time.  The  ice  ivould  have  behaved  precise- 
ly like  a  viscous  body.  Now,  this  is  precisely  what  takes  place  in  a  glacier. 

Application  to  Glaciers. — A  glacier,  on  account  of  its  immense  mass, 
is,  in  its  lower  parts,  under  the  heavy  pressure  of  its  own  weight 
tending  to  mold  it  to  the  inequalities  of  its  own  bed,  and  in  every  part 
under  a  still  more  powerful  pressure — a  pressure  proportioned  to  the 
height  of  the  head  of  the  glacier — urging  it  down  the  slope  of  its  bed. 
Under  the  influence  of  this  pressure  the  mass  is  continually  yielding  by 


fracture  of  all  sizes,  but,  after  changing  the  position  of  its  parts,  again 
tmiting  by  regelation.  By  this  constant  process  of  crushing,  change  of 
form,  and  reunion,  the  glacier  behaves  like  a  plastic  or  viscous  body ; 
though  of  true  plasticity  or  true  viscosity  there  is,  according  to  Tyn- 
dall, none.  In  fact,  we  have  in  the  phenomena  of  glaciers  the  most 
delicate  test  of  viscosity  conceivable ;  but  we  find  the  glaciers  will  not 
stand  the  test.  For  instance,  the  slope  of  the  Mer  de  Glace  at  one 
point  changes  from  4°  to  9°  25'*  (Fig.  55),  and  yet  the  glacier,  although 

*  Tyndall,  Glaciers  of  the  Alps. 


RECENT   THEORIES.  05 

moving  but  two  feet  a  day,  can  not  make  this  slight  bend  without  rupt- 
ure ;  for  at  this  point  there  are  always  large  transverse  fissures  which 
heal  up  below  by  pressure  and  regelation.  In  another  place  the  gla- 
cier is  similarly  broken  by  passing  an  angle  produced  by  a  change  of 
slope  of  only  2°.  It  seems  almost  impossible  that  a  body  having  the 
slightest  viscosity  should  be  fractured  under  these  circumstances.  Tyn- 
dall  concludes,  therefore,  that  the  motion  of  glaciers  is  viscoid,  but 
the  body  is  not  viscous — the  viscoid  motion  being  the  result,  not  of  the 
property  of  viscosity,  but  of  fracture,  change  of  position,  and  regela- 
tion. 

Comparison  of  the  Two  Theories. — Forbes's  theory  supposes  motion 
among  the  ultimate  particles,  without  rupture.  Tyndall's  supposes 
motion  among  discrete  particles  by  rupture,  change  of  position,  and 
regelation.  The  undoubted  viscoid  motion  is  equally  explained  by 
both :  by  the  one,  by  a  property  of  viscosity  ;  by  the  other,  by  a  prop- 
erty of  regelation.  There  can  be  little  doubt  that  both  views  are  true, 
and  that  both  properties  are  concerned  in  glacial  motion. 

Recent  Theories. 

droll's  Theory. — Croll  has  recently,  in  his  work  on  Climate  and 
Time,  brought  forward  a  theory  which  has  attracted  much  attention. 
Moseley  had  previously  attempted  to  prove  the  untenableness  of  all 
theories  attributing  the  motion  of  glaciers  to  gravity,  by  showing  ex- 
perimentally that  the  shearing  force  of  ice  (the  force  necessary  to 
slide  one  layer  on  another,  as  in  differential  motion)  is  many  times 
greater  than  that  portion  of  gravity  which  acts  in  the  direction  of  the 
slope  of  a  glacial  bed.  Croll,  accepting  Moseley's  view  in  regard  to 
the  shearing  force  of  ice,  but  accepting  also  gravity  as  the  moving 
force  of  glaciers,  thinks  to  reconcile  these  by  supposing  that  there  is  in 
ice,  when  subjected  to  heat,  a  momentary  loss  of  cohesion  by  melting, 
which  is  transferred  from  molecule  to  molecule,  giving  rise  thereby  to 
a  kind  of  intestine  molecular  motion  similar  in  its  effects  to  viscosity. 
The  process  is  as  follows :  Heat  falling  on  glacier-ice  melts  its  sur- 
face. The  water  thus  formed  runs  down  to  a  lower  level,  and  is 
again  refrozen.  Now,  what  takes  place  conspicuously  on  the  surface 
takes  place  molecularly  in  the  interior  of  the  icqi  In  every  part  the 
ice-molecules  are  melting  and  refreezing.  A  molecule  takes  up  heat 
by  melting,  runs  down  to  an  infinitesimally  lower  point,  refreezes,  and 
in  so  doing  gives  up  its  heat  and  melts  another  molecule,  -which  in  its 
turn  seeks  a  lower  position,  and,  by  refreezing,  transfers  its  heat  and 
fusion  to  still  another  molecule,  and  so  on.  Thus  the  whole  glacier  is 
in  a  state  of  molecular  movement  downward. 

The  theory  is  ingenious,  but  somewhat  obscure.  We  will,  there- 
fore, dismiss  it  with  two  remarks :  1.  Moseley's  objection  to  gravity  as 
5 


66  AQUEOUS  AGENCIES. 

the  moving  force  of  glaciers  is  invalidated  by  the  fact  that  he  does 
not  take  sufficiently  into  account  the  effect  of  time  and  slowly -applied 
pressure  in  determining  shearing ;  and  in  stiffly  viscous  substances 
time  is  the  controlling  element.  2.  Until  we  understand  better  than 
we  now  do  the  actual  behavior  of  ice-molecules  in  glacial  motion, 
CrolPs  theory  must  be  regarded  only  as  a  modification  (though,  per- 
haps, an  important  modification)  of  Forbes's ;  for  it  supposes  a  mo- 
lecular differential  motion  determined  by  gravity,  and  into  which  both 
heat  and  time  enter  as  elements.  It  is  an  attempted  physical  explana- 
tion of  the  viscosity  of  ice. 

Thomson's  Theory. — Some  time  ago  James  Thomson  brought  for- 
ward a  theory  which  deserves  far  more  attention  than  it  has  yet  re- 
ceived. Thomson  shows  that  the  fusing-point  of  ice  is  loioered,  and, 
therefore,  that  ice  at  or  near  its  fusing-point  (as  is  the  fact  in  glaciers) 
is  promptly  melted  by  pressure.  Now,  it  is  obvious  that,  in  the  dif- 
ferential motion  of  glaciers,  whatever  point  at  any  moment  receives 
the  greatest  stress  of  pressure  must  melt  and  give  way,  and,  the  stress 
being  relieved,  it  must  immediately  again  refreeze.  Meantime,  by 
change  of  relative  position  of  parts,  the  stress  is  transferred  to  some 
other  point,  which  in  its  turn  melts,  gives  way,  is  refrozen,  and  trans- 
fers its  stress  to  still  another  point,  and  so  on.  If  we  compare  this 
theory  with  TyndalPs,  in  both  cases  the  ice  gives  way  at  the  point  of 
greatest  stress — in  the  one  case  stress  of  tension,  in  the  other  of  press- 
ure— in  the  one  case  by  fracture,  in  the  other  by  melting.  Differential 
motion,  therefore,  in  the  one  case  is  by  fracture,  change  of  position, 
and  regelation  ;  in  the  other  by  melting,  change  of  position,  and  reye- 
lation. 

Structure  of  Glaciers. 

There  are  two  points  connected  with  the  structure  of  glaciers  which 
require  notice,  viz.,  the  veined  structure  and  the  fissures. 

Veined  Structure. — The  ice  of  glaciers  is  not  homogeneous,  but  con- 
sists of  white  vesicular  ice  (white  because  vesicular),  banded,  often  very 
beautifully,  with  solid  transparent  blue  ice  (transparent  blue  because 
solid),  the  banding  sometimes  so  delicate  that  a  hand-specimen  looks 
like  striped  agate.  These  blue  veins  are  not  continuous  planes,  but 
apparently  very  flat  lenticular  in  shape,  varying  in  thickness  from  a 
line  to  several  inches,  and  in. length  from  a  few  inches  to  several  feet. 
Their  direction  being  parallel  to  one  another,  they  give  a  stratified  or 
cleavage  structure  to  the  glacier,  and,  in  melting,  the  glacier  often 
splits  or  cleaves  along  these  planes.  According  to  Prof.  Forbes,  look- 
ing upon  the  glacier  as  a  whole,  we  may  regard  the  strata  as  taking 
the  form  represented  by  the  subjoined  figures.  In  a  section  parallel  to 
the  surface  (Fig.  56,  a),  the  strata  outcrop  in  the  form  of  loops.  A 
cross-section  (Fig.  56,  b)  shows  them  lying  in  troughs,  and  a  longi- 


THEORIES  OF  STRUCTURE. 


67 


tudinal  vertical  section  (Fig.  56,  c)  shows  the  manner  in  which  they 
dip.    Fig.  57  is  an  ideal  glacier  cut  in  several  directions,  and  combining 


Fiu.  56.— Sections  of  a  Glacier. 


Pio.  57.  —  Ideal  Diagram,  showing 
Structure  of  Glacier*  (after  Forbes). 


in  one  view  the  three  sections  given  above.  It  is  generally  impossible 
to  trace  the  veins  around  from  side  to  side.  Sometimes  they  are  most 
distinct  on  the  margins,  and  then  are  called  marginal  veins ;  some- 
times at  the  point  of  the  loop — transverse  veins  ;  sometimes  tributaries 
running  together,  as  in  the  figure  (Fig.  57) — the  interior  branches  of 
the  two  loops*  coalesce,  and  are  flattened  against  one  another,  and  form 
longitudinal  veins. 

Fissures. — These  are  also  marginal,  transverse^  and  longitudinal. 
The  marginal  fissures  are  shown  in  Fig.  43 ;  they  are  always  at  right 
angles  to  the  marginal  veins. 

Theories  of  Structure. 

Fissures. — There  can  be  no  doubt  that  the  great  fissures  or  crevasses 
are  produced  by  tension  or  stretching y  and  that  their  direction  is  always 
at  right  angles  to  the  line  of  greatest  tension.  Thus  the  transverse 
fissures  are  produced  by  the  stretching  of  the  glacier  in  passing  over  a 
salient  angle.  The  marginal  fissures  are  produced  by  the  dragging  or 
pulling  of  the  swifter  central  portions  upon  the  slower  marginal  por- 
tions. It  has  been  proved  by  Hopkins,  the  English  physicist  and  geolo- 
gist, that  the  line  of  greatest  tension  from  this  cause  would  be  inclined 
45°,  with  the  course  of  the  glacier  as  shown  by  the  arrows  (Fig.  58). 
The  fissures  should  be  at  right  angles  to  these  lines,  and,  therefore,  also 
inclined  45°  with  the  margin,  and  running  upward  and  inward.  The 
longitudinal  fissures  are  best  seen  where  a  glacier  runs  through  a  nar- 


68 


AQUEOUS  AGENCIES. 


FIG.  58. 


FIG.  59. 


FIG.  60. 


row  gorge  out  on  an  open  plain.  The  lateral  spreading  of  the  glacier 
causes  it  to  crack  longitudinally  (Fig.  59).  Fig.  GO^s  a  longitudinal 
vertical  section  of  the  same. 

Veined  Structure. — Tyndall  has  shown  conclusively  that  veins  are 
always  at  right  angles  to  the  line  of  greatest  pressure,  and  that,  there- 
fore, they  are  produced  by  press- 
ure. Thus  fissures  and  veins, 
being  produced  by  opposite 
causes — one  by  tension  and  the 
other  by  pressure — are  formed 
under  opposite  conditions.  As 
transverse  fissures  are  produced 
by  the  longitudinal  stretching 
of  a  glacier  passing  over  a  sa- 
lient angle,  so  transverse  veins 
are  formed  by  the  longitudinal 
compression  of  a  glacier  passing 

over  a  re-entering  angle.  Fig.  60  is  a  section  of  the  Rhone  glacier 
(Fig.  59),  showing  the  crevasses  (c  c  c)  produced  by  the  steep  declivity, 
and  the  veined  structure  (s  s  s)  produced  by  the  compression  conse- 
quent upon  the  change  of  angle  on  coming  out  on  the  plain.  The 
relation  of  crevasses  and 
vein-structure  is  still  bet- 
ter shown  in  the  ideal  sec- 
tion (Fig.  61). 

Again,  as  marginal  fis- 
sures are  produced  by  the 
pulling  of  the  central  por- 
tions upon  the  lagging 
margins  behind,  so  the 

marginal  veins  are  produced  by  the  crowding  or  pushing  of  the  swifter 
central  parts  on  the  slower  marginal  parts  in  front  (Fig.  62).  The 
marginal  veins  are,  therefore,  inclined  to  the  margin  about  45°,  but 


THEORIES   OF  STRUCTURE. 


69 


pointing  inward  and  doivnward,  and,  therefore,  at  right  angles  to  the 
crevasses.     The  relation  of  these  to  one  another  is  shown  in  Fig.  63. 

Finally,  as  longitudinal  fissures  are  produced  by  lateral  spreading 
(Fig.  59),  so  longitudinal  veins  are  produced  by  lateral  compression. 
This  is  best  seen  where  two  tributaries  meet  at  a  high  angle  (Fig.  64) — 
for  instance,  where  the  Glacier  du  Geant  and  the  Glacier  de  Lechaud 


FIG.  62, 


FIG.  63. 


FIG.  64. 


form  the  Mer  de  Glace  (Fig.  44).     All  these  facts  have  been  experi- 
mentally illustrated  by  Tyndall. 

Physical  Theory  of  Veins.— There  is  little  doubt  that  veins  are 
formed  by  pressure  at  right  angles  to  the  direction  of  the  veins;  but 
how  pressure  produces  this  structure  is  very  imperfectly  understood. 
Probably  at  least  a  partial  explanation  is  contained  in  the  following 
propositions :  1.  White  vesicular  ice  by  powerful  pressure  is  crushed,  the 
air  escapes,  and  the  ice  is  refrozen  into  solid  blue  transparent  ice.  2. 
Ice  being  a  substance  which  expands  in  freezing,  and,  therefore,  con- 
tracts in  melting,  its  freezing  and  melting  point  is  lowered  by  pressure. 
Therefore,  ice  at  or  near  32°  Fahr.  is  melted  by  pressure.  Now,  the 
glacier  is  under  powerful  pressure  of  its  own  weight,  and  the  stress  of 
this  pressure  is  ever  changing  from  point  to  point  by  the  changing 
position  of  the  particles  produced  by  the  motion.  Thus  the  glacier  in 
places  is  ever  melting  under  pressure,  and  again  refreezing  by  relief  of 
pressure.  The  melting  discharges  the  air-bubbles,  and,  in  refreezing, 
the  ice  is  blue.  3.  No  substance  is  perfectly  homogeneous,  and  of 
equal  strength  in  all  parts ;  therefore,  this  crushing  and  melting,  and 
consequent  conversion  of  white  into  blue  ice,  take  place  irregularly  in 
spots.  4.  As  ice  of  a  glacier  acts  like  a  viscous  substance,  the  final 
effect  of  pressure  would  be  to  flatten  these  spots,  both  white  and  blue, 
in  the  direction  of  greatest  pressure,  and  extend  them  in  a  direction  at 
right  angles  to  the  pressure,  and  thus  create  bands  in  this  direction.  5. 
Differential  motion  would  also  tend  to  bring  the  veins  into  the  direction 
indicated  by  Forbes. 


70 


AQUEOUS  AGENCIES. 


Floating  Ice — Icebergs. 

We  have  already  seen  (page  50)  that  at  a  certain  latitude,  varying 
from  46°  in  South  America  to  about  65°  in  Norway,  glaciers  touch  the 
surface  of  the  ocean.  Beyond  this  latitude,  they  run  out  to  sea  often  to 
great  distances.  By  the  buoyant  power  of  water,  assisted  by  tides  and 
waves,  these  projecting  floating  masses  are  broken  off,  and  accumulate 
as  immense  ice-barriers  in  polar  seas,  or  are  drifted  away  by  currents 
toward  the  equator.  Such  floating  fragments  of  glaciers  are  called  ice- 
bergs. Fig.  65  is  an  ideal  section,  through  a  glacial  valley,  in  which 
a  g  is  the  glacier,  ~b  the  cliffs  beyond,  I  s'  the  sea-level,  and  i  an  iceberg. 


FIG.  65.— Formation  of  Icebergs. 

The  principal  source  of  the  icebergs  of  the  north  Atlantic  is  the 
coast  of  Greenland.  This  country  is  an  elevated  table-land,  sloping 
in  every  direction  to  a  coast  deeply  indented  like  Norway,  with  alter- 
nate deep  fiords  and  jutting  headlands.  The  whole  table-land  is  com- 
pletely covered  with  an  ice-slieet,  probably  several  thousand  feet  thick, 
moving  slowly  seaward,  and  discharging  through  the  fiords  as  immense 
glaciers,*  which,  as  already  explained,  form  icebergs.  In  this  remarka- 
ble country  no  water  falls  from  the  atmosphere  except  in  the  form  of 
snow,  and  all  the  rivers  are  glaciers.  The  geological  effects  of  such  a 
moving  ice-sheet  may  be  easily  imagined.  The  whole  surface  of  the 
country  rock  must  be  polished  and  scored,  the  general  direction  of  the 
striae  being  parallel  over  large  areas. 

The  antarctic  continent  is  probably  similarly,  and  even  more  thick- 
ly, ice-sheeted,  for  the  humid  atmosphere  of  that  region  is  very  favorable 
to  the  accumulation  of  snow  and  ice.  Captain  Wilkes  found  an  impen- 
etrable ice-barrier,  in  many  places  150  to  200  feet  high,  for  1,200  miles 
along  that  coast.  From  this  ice-barrier,  icebergs  separate  and  are  drifted 
toward  the  equator. 

*  Dr.  Rink,  Archives  des  Sciences,  vol.  xxvii,  p.  155. 


FLOATING   ICE— ICEBERGS. 


71 


The  formation  of  icebergs  in  polar  regions,  and  their  drifting  into 
warmer  latitudes,  to  be  melted  there,  are  evidently  a  necessary  conse- 
quence of  the  great  law  of  circulation,  for  otherwise  ice  would  accumu- 
late without  limit  in  these  regions.  But,  by  glacial  motion,  the  excess 
is  brought  down  to  the  sea,  broken  off  as  icebergs,  carried  southward 
by  currents,  and  there  melted  and  returned  into  the  general  circulation 
of  meteoric  waters. 

General  Description. — The  number  of  icebergs  accumulated  about 
polar  coasts  is  almost  inconceivable.  Scoresby  counted  500  at  one 


FIG.  66. 

view.  Kane  counted  280  of  the  first  magnitude  at  one  view.  They 
are  often  200  and  sometimes  even  400  feet  high,  and  the  mass  above 
water  66,000,000  cubic  yards  (Dr.  Rink).  As  the  specific  gravity  of 
ice  is  0-918,  if  these  were  solid  ice,  there  would  be  but  one  twelfth 
above  water;  but  as  glacier-ice  is  somewhat  vesicular,  there  is  about 
one  seventh  above  water.  The  thickness  of  some  of  these  icebergs 
must  therefore  be  2,000  to  3,000  feet,  and  their  volume  near  500,000,000 
cubic  yards,  which  is  about  equivalent  to  a  mass  one  mile  square  and 


FIG.  67. 


72  AQUEOUS  AGENCIES. 

500  feet  thick.  Under  the  influence  of  the  melting  power  of  the  sun  un- 
equally affecting  different  parts,  they  assume  various  and  often  strange 
forms.  The  accompanying  figure  (Fig.  66)  gives  the  usual  appearance 
in  the  northern  Atlantic.  Those  separated  from  the  antarctic  barrier 
present,  before  they  have  been  much  acted  upon  by  the  sun,  a  much 
more  regularly  prismatic  appearance.  Fig.  67  gives  the  appearance  of 
one  of  these  prismatic  blocks  or  tables,  180  feet  high,  seen  by  Sir  James 
Ross  in  the  antarctic  seas. 

Icebergs  as  a  Geological  Agent— Erosion. — The  polishing  and  scor- 
ing effects  of  the  ice-sheets  and  of  their  discharging  glaciers  must,  of 
course,  extend  over  the  sea-bottoms  about  polar  coasts  as  far  as  the 
glaciers  touch  bottom,  which,  considering  their  immense  thickness, 
must  be  for  considerable  distances  (Fig.  65,  s'  to  (/).  This,  however,  is 
glacier  agency  rather  than  iceberg  agency.  On  being  separated  they 
float  away,  and  are  carried  by  currents  with  their  immense  loads  of 
earth  and  bowlders,  amounting  often  to  100,000  tons  or  more,  as  far 
as  40°  or  even  36°  latitude,  where,  being  gradually  melted,  they  drop 
their  burden.  If  the  water  be  not  sufficiently  deep,  they  ground,  and 
being  swayed  by  waves  and  tides  they  chafe  and  score  the  bottom  in  a 
somewhat  irregular  manner ;  or,  packing  together  in  large  fields,  and 
urged  onward  by  powerful  currents,  they  may  possibly  score  the  bot- 
tom over  considerable  areas  somewhat  in  the  manner  of  glaciers.  A 
large  iceberg  will  ground  in  water  2,000  and  2,500  feet  deep ;  they 
have  been  found  by  James  Ross  actually  aground  in  1,560  feet  of  water 
off  Victoria  Land.  A  true  glaciated  surface,  however,  can  not  be  pro- 
duced by  icebergs. 

Deposits. — The  bottom  of  the  sea  about  polar  shores  is  found  deep- 
ly covered  with  the  materials  brought  down  by  glaciers  and  dropped 
by  icebergs  (Fig.  65).  Again,  similar  materials  are  carried  by  icebergs 
as  far  as  these  are  drifted  by  currents,  and  spread  on  the  bottom  of  the 
sea  everywhere  in  the  course  of  these  currents.  Where  stranded  ice- 
bergs accumulate,  as  on  the  banks  of  Newfoundland,  large  quantities  of 
such  materials  are  deposited.  These  banks  are  jn  fact  supposed  to 
have  been  formed,  in  part  at  least,  in  this  way.  Such  deposits  have 
not  been  sufficiently  examined  ;  they  are  probably  somewhat  similar  to 
those  of  glaciers,  exhibiting,  however,  some  signs  of  the  sorting  power  of 
water.  Balanced  stones  or  bowlders  in  insecure  positions  can  hardly 
be  left  by  icebergs. 

Shore-Ice. 

In  cold  climates  the  freezing  of  the  surface  of  the  water  forms 
sheets  of  ice  many  inches  or  even  feet  thick,  and  of  great  extent,  about 
the  shores  of  rivers,  bays,  and  seas.  They  often  inclose  stones  and 
bowlders  of  considerable  size,  and  when  loosened  in  spring  from  the 
shore  they  bear  these  away,  and  again  drop  them  at  considerable  dis- 


MECHANICAL   AGENCIES   OF   WATER.  73 

tances  from  their  parent  rock.  Also  such  sheets  packed  together  in 
large  masses,  and  driven  ashore  by  river  and  tidal  currents,  and  chafed 
back  and  forth  by  waves,  produce  effects  on  the  shore-rocks  somewhat 
similar  to  the  scoring,  polishing,  and  even  the  roches  moutonnees  of 
glacier-action.  On  a  rising  or  on  a  subsiding  coast  such  scorings  and 
polishings  may  extend  over  wide  areas,  and  thus  simulate  true  glacial 
action.  These  effects  are  well  seen  on  the  shores  of  the  St.  Lawrence 
liiver  and  Gulf. 

The  importance  of  the  study  of  ice-agencies  will  be  seen  when  we 
come  to  explain  the  phenomena  of  the  Drift  or  Glacial  period. 

Comparison  of  the  Different  Forms  of  the  Mechanical  Agencies  of 

Water. 

Rivers  and  glaciers  are  constantly  cutting  down  all  lands,  bearing 
away  the  materials  thus  gathered,  and  depositing  them  on  the  sea- 
margins.  Acting  alone,  therefore,  their  effect  must  be  to  diminish  the 
height  and  to  extend  the  limits  of  the  land.  Ocean  agencies,  on  the 
other  hand,  by  tides  and  currents  bear  away  to  the  open  sea  the  mate- 
rials brought  down  from  the  land,  and  thus  tend  to  prevent  marginal 
accumulations ;  and  by  waves  and  tides  constantly  eat  away  the  coast- 
line, and  thus  strive  to  extend  the  domain  of  the  sea.  Thus,  while 
river  and  ocean  agencies  are  in  conflict  with  one  another  at  the  coast- 
line, the  one  striving  to  extend  the  limits  of  the  land,  and  the  other 
of  the  sea,  yet  they  co-operate  with  each  other  in  destroying  the  in- 
equalities of  the  earth's  surface,  and  are  therefore  called  leveling  ai/c/i- 
cies.  Moreover,  it  is  evident  that  the  erosion  of  the  land  and  the  fill- 
ing up  of  the  seas  are  correlative,  and  one  is  an  exact  measure  of  the 
other.  Now,  we  have  seen  (page  11)  that  the  probable  rate  at  which 
all  continents  are  being  cut  down  by  rivers  is  about  one  foot  in  4,500  to 
5,000  years.  But  since  the  ocean  is  about  three  times  the  extent  of 
the  land,  this  spread  evenly  over  the  bottom  of  the  sea  would  make  a 
stratum  about  four  inches  thick.  Therefore,  we  conclude  that,  neg- 
lecting the  destructive  effects  of  waves  and  tides  on  the  coast-line, 
which,  according  to  Phillips,*  are  small  in  amount  compared  with  gen- 
eral erosion  of  the  land-surface,  we  may  say  that  stratified  deposits  are 
now  forming,  or  the  ocean-bed  filling  up,  at  the  average  rate  over  the 
whole  bottom  of  about  four  inches  in  5,000  years. 

*  Phillips,  Life  on  the  Earth,  p.  13  L 


74:  AQUEOUS  AGENCIES. 

SECTION  4. — CHEMICAL  AGENCIES  OF  WATEK. 
Subterranean  Waters,  Springs,  etc. 

As  we  have  already  seen  (page  9),  of  the  rain  which  falls  on  any 
hydrographical  basin,  a  part  runs  from  the  surface,  producing  universal 
erosion.  A  second  part  sinks  into  the  earth,  and,  after  a  longer  or 
shorter  subterranean  course,  comes  up  as  springs,  and  unites  with  the 
surface-water  to  form  rivers ;  while  a  third  portion  never  comes  up  at 
all,  but  continues  by  subterranean  passages  to  the  sea.  This  last  por- 
tion is  removed  from  observation,  and  our  knowledge  concerning  it  is 
very  limited.  But  there  are  numerous  facts  which  lead  to  the  convic- 
tion that  it  is  often  very  considerable  in  amount.  In  many  portions  of 
the  sea  near  shore,  springs,  and  even  large  rivers,  of  fresh  water,  are 
known  to  well  up.  Thus,  in  the  Mediterranean  Sea,  "  a  body  of  fresh 
water  fifty  feet  in  diameter  rises  with  such  force  as  to  cause  a  visible 
convexity  of  the  sea-surface."*  Similar  phenomena  have  been  ob- 
served in  many  other  places  in  the  same  sea,  and  also  in  the  Gulf  of 
Mexico  near  the  coast  of  Florida,  among  the  West  India  Isles,  and  near 
the  Sandwich  Islands.  Besides  the  last  mentioned,  there  is  still  another 
portion  of  subterranean  water  existing  permanently  in  every  part  of 
the  earth  far  beneath  the  sea-level,  filling  fissures  and  saturating  sedi- 
ments to  great  depths,  and  only  brought  to  the  surface  by  volcanic 
forces.  This,  in  contradistinction  from  the  constantly-circulating  me- 
teoric water,  may  be  called  volcanic  water. 

Springs. — The  appearance  of  subterranean  waters  upon  the  surface 
constitutes  springs.  They  occur  in  two  principal  positions,  viz. :  1. 


FIG.  68.— Hill-side  Spring.  FIG.  69. 

Upon  Mil-sides,  just  where  porous,  water-bearing  strata  such  as  sand 
outcrop,  underlaid  by  impervious  strata  like  clay  ;  2.  On  fissures  pene- 
trating the  country  rock  to  great  depth. 

Most  of  the  small  springs  occurring  everywhere  belong  to  the  first 
class.  The  figure  (Fig.  68)  represents  a  section  of  a  hill  composed 
mostly  of  porous  strata,  #,  but  underlaid  by  impervious  clay  stratum,  c. 
Water  falling  upon  the  surface  sinks  through  b  until  it  comes  in  contact 

*  Herschel's  Physical  Geography. 


SUBTERRANEAN   WATERS,   SPRINGS,   ETC. 


75 


Flo.  70. — Fissure-Spring. 


with  c,  and  then  by  hydrostatic  pressure  moves  laterally  until  it  emerges 
at  a.  Sometimes  this  is  a  geological  agent  of  considerable  importance, 
modifying  even  the  forms  of  mountains,  and  producing  land-slips,  etc. 
Thus  the  Lookout  and  Raccoon  Mountains,  in  Tennessee,  are  table- 
mountains  of  nearly  horizontal  strata,  separated  by  erosion-valleys. 
These  mountains  are  all  of  them  capped  by  a  sandstone  stratum  about 
100  feet  thbk,  underlaid  by  shale.  The  water  which  falls  upon  the 
mountain  emerges  in  numerous  springs  all  around  where  the  sandstone 
cap  comes  in  contact  with  the  underlying  shale.  The  sandstone  is 
gradually  undermined,  and  falls 
from  time  to  time,  and  thus  the 
cliff  remains  always  perpendic- 
ular (Fig.  69). 

Large  springs  generally  is- 
sue from  fissures.  Water  pass- 
ing along  the  porous  stratum  b, 
perhaps  from  great  distance,  and  prevented  from  rising  by  the  over- 
lying impervious  stratum  c,  coming  in  contact  with  a  fissure,  immedi- 
ately rises  through  it  to  the  surface  at  a  (Fig.  70). 

Artesian  Wells. — If  subterranean  streams  have  their  origin  in  an 
elevated  region,  a  d,  composed  of  regular  strata  dipping  under  a  lower 
flat  country,  c,  then  the  subterranean  waters  passing  along  any  porous 
stratum  as  a  (Fig.  71),  and  confined  by  two  impermeable  strata,  b  and 

d,  will  be  under  powerful 
d.  /T^  hydrostatic  pressure,  and 
will,  therefore,  rise  to  the 
surface,  perhaps  with  con- 
siderable force,  if  the  stream 
be  tapped  by  boring  at  c. 
Borings  by  which  water  is 
obtained  in  this  manner  are 
called  Artesian  wells,  from  the  French  province  Artois,  where  they  were 
first  successfully  attempted.  The  source  of  the  water  may  be  100  miles 
or  more  distant  from  the  well.  Some  of  these  wells  are  very  deep.  The 
Grenelle  Artesian  in  Paris  is  2,000  feet  deep.  At  the  moment  of  tapping 
the  stream,  a  powerful  jet  was  thrown  112  feet  high.  One  in  West- 
phalia, Germany,  is  2,385  feet  deep  ;  one  at  St.  Louis,  3,843  feet ;  one 
at  Louisville,  Kentucky,  2,852;  one  near  Berlin,  4,172  feet;  one  near 
Pittsburg,  Pa.,  4,625  ;  and  one  near  Leipsic,  5,735  feet.*  In  parts  of 
Alabama  and  California  the  principal  supply  of  water  for  agricultural 
purposes  is  drawn  from  these  wells. 

Thus  there  is  on  all  coasts  a  constant  flowing  of  water,  both  super- 


FIG.  71.— Artesian  Well. 


*  Science,  xiv,  p.  250,  1889. 


76 


AQUEOUS  AGENCIES. 


ficial  and  subterranean,  into  the  sea.  Their  relative  amount  it  is  impos- 
sible to  determine.  Much  depends  upon  the  configuration  of  the  coun- 
try and  the  nature  of  the  strata.  The  heavy  hydrostatic  pressure  to 
which  subterranean  water  is  subjected,  especially  in  elevated  countries, 
brings  the  larger  portion  of  it  to  the  surface  as  springs.  But,  in  lime- 
stone regions  (this  rock  being  affected  with  frequent  and  large  fissures, 
and  open  subterranean  passages,  as  will  be  hereafter  explained),  large 
subterranean  rivers  often  exist,  and  these,  even  after  coming  to  the  sur- 
face are  often  re-engulfed,  and  finally  reach  the  sea  by  subterranean 
passages.  The  same  is  true  also  of  regions  covered  with  recent  lava- 
flows;  for  these  also  are  full  of  caves  and  galleries  (page  92).  The 
largest  springs,  therefore,  generally  occur  either  in  limestone  or  in  vol- 
canic countries.  From  the  Silver  Spring,  in  Florida,  issues  a  stream 
navigable  for  small  steamers  up  to  the  very  spring  itself.  The  country 
for  sixty  miles  around  is  entirely  destitute  of  superficial  streams,  the 
whole  drainage  being  subterranean,  and  coming  up  in  this  spring.* 
About  Mount  Shasta  all  the  streams  head  in  great  springs. 

Chemical  Effects  of  Subterranean  Waters. — We  have  already  seen 
(page  6)  how  atmospheric  water  disintegrates  rocks,  dissolving  out 
their  soluble  parts,  and  reducing  their  unsoluble  parts  to  soils.  Springs, 
therefore,  always  contain  these  soluble  matters.  In  granite  regions 
they  contain  potash ;  in  limestone  regions  they  contain  lime,  and  are 
called  hard ;  in  other  cases  they  contain  salt,  and  are  brackish  ;  when 
the  saline  ingredients  are  unusual  in  quantity  or  in  kind,  they  are 
\called  mineral  waters. 

Limestone  Caves. — In  most  rocks,  the  insoluble  part  left  as  soil  is 
far  the  largest,  only  a  small  percentage  being  dissolved.     In  such  rocks, 

therefore,  the  resulting 
soil  fills  the  whole  space 
originally  occupied  by 
the  rock.  But  in  the 
case  of  limestone  the 
whole  rock  is  soluble. 
Therefore,  in  limestone 
regions,  percolating  wa- 
ters dissolve  the  lime- 
stone, hollow  out  open 

F,G.  72.-Lime8tone  Cave.  passages,  and  form  im- 

mense     caves.        Water 

charged  with  limestone,  dripping  from  the  roofs  and  falling  on  the 
floors  of  these  caves,  deposit  their  limestone  by  evaporation,  and  form 


. 


*  The  exceptional  transparency  of  limestone  waters  is  due  to  the  property,  possessed 
by  lime  in  a  remarkable  degree,  of  flocculating  and  precipitating  clay  sediments. 


CHEMICAL   DEPOSITS   IN   SPRINGS.  77 

stalactites  (Fig.  72),  a  a,  and  stalagmites,  b  b,  which,  meeting  each 
other,  form  limestone  pillars,  c  c.  The  great  Mammoth  Cave,  in  Ken- 
tucky ;  Wier's  Cave,  in  Virginia,  and  Nicojack  Cave,  in  Tennessee,  are 
familiar  examples.  As  might  be  expected,  subterranean  rivers  are 
often  found  in  these  caves.  This  is  the  case  in  the  Mammoth  Cave 
and  in  Nicojack  Cave. 

Thus,  as  the  same  river  will  erode  or  deposit  according  as  it  is 
under-loaded  or  overloaded  with  sediment ;  so  the  same  underground 
stream  may  hollow  out  passages  by  solution  or  fill  them  up  by  deposit 
according  as  its  waters  are  under-saturated  or  over-saturated  with  min- 
eral matter. 

There  are  many  other  effects  of  subterranean  waters  of  the  greatest 
importance,  such  as  the  formation  of  fossils,  the  filling  of  mineral 
veins,  the  metamorphism  of  rocks,  etc. ;  but  these  will  be  taken  up 
each  in  its  appropriate  place. 

Chemical  Deposits  in  Springs. 

Deposits  of  Carbonate  of  Lime. — We  have  just  seen  that  ordinary 
subterranean  waters  in  limestone  districts,  and,  therefore,  containing 
small  quantities  of  carbonate  of  lime,  deposit  this  substance  only  very 
slowly  by  drying,  as  stalactites  and  stalagmites;  but  in  carbonated 
springs  in  limestone  districts  a  very  rapid  deposit  of  lime  carbonate 
often  occurs. 

Explanation. — In  order  to  understand  this,  it  is  necessary  to  re- 
member :  1.  That  lime  carbonate  is  insoluble  in  pure  water,  but  soluble 
in  water  containing  carbonic  acid ;  2.  That  the  amount  of  carbonate 
dissolved  is,  up  to  a  limit,  proportionate  to  the  amount  of  carbonic  acid 
contained ;  3.  That  the  amount  of  carbonic  acid  which  may  be  taken 
in  solution  by  water  is  proportionate  to  the  pressure. 

Now,  there  are  two  sources  of  carbonic  acid,  viz.,  atmospheric  and 
subterranean.  All  water  contains  carbonic  acid  from  the  atmosphere, 
and  will,  therefore,  dissolve  limestone,  but  this  deposits  only  slowly  by 
drying,  as  already  explained.  But  in  many  districts,  especially  in  vol- 
canic districts,  there  are  abundant  subterranean  sources  of  carbonic 
acid.  If  subterranean  waters  come  in  contact  with  such  carbonic  acid, 
being  under  heavy  pressure,  they  will  take  up  a  large  quantity  of  this 
gas ;  and  if  such  water  comes  to  the  surface,  the  pressure  being  re- 
moved, the  gas  will  escape  in  bubbles.  This  is  a  carbonated  spring. 
If,  further,  the  subterranean  waters,  thus  highly  charged  with  carbonic 
acid,  come  in  contact  with  limestone  rocks,  or  rocks  of  any  kind  con- 
taining lime  carbonate,  they  will  dissolve  a  proportionately  large  amount 
of  this  carbonate ;  and  when  they  come  to  the  surface,  the  escape  of 
the  carbonic  acid  causes  the  lime  carbonate  to  deposit  abundantly. 
Thus  around  carbonated  springs  in  limestone  districts,  and  along  the 


78 


AQUEOUS  AGENCIES. 


course  of  the  streams  which  issue  from  them,  are  generally  found  ex- 
tensive deposits  of  this  substance.  Being  found  mostly  in  volcanic 
regions,  these  springs  are  commonly  hot. 

Kinds  of  Materials, — The  material  thus  deposited  is  usually  called 
travertine,  but  is  very  diverse  in  appearance.  If  the  deposit  is  quiet, 
the  material  is  dense ;  if  tumultuous,  the  material  is  spongy ;  if  no 
iron  is  present,  it  is  white  like  marble ;  but  if  iron  be  present,  its  oxida- 
tion colors  it  yellow,  brown,  or  reddish.  If  the  amount  of  iron  be  vari-. 
able,  the  stone  is  beautifully  striped.  If  objects  of  any  kind,  branches, 
twigs,  leaves,  are  immersed  in  such  waters,  they  are  speedily  incrusted, 
often  in  the  most  beautiful  manner. 

Examples  of  such  deposits  are  found  in  all  countries.    At  the  baths 
of  San  Vignone,  Italy,  a  carbonated  spring  issuing  from  the  top  of  a 
hill  has  covered  the  hill  with  a  stratum  of 
white,  compact  travertine  250  feet  thick. 
In  the  conduit-pipe  which  leads  the  water 
to  the  baths,  the  deposit  accumulates  six 
inches  thick  every  year.     A  similar  deposit 
of   travertine  occurs  at  the  baths  of  San 
Filippo.      At  this  latter  place,   beautiful 
fac- similes  of  medallions,  coins,  etc.,  are 
formed  by  placing  these  objects  of  art  in 
the   spray   of   an   artificial   cascade. 
In     Virginia,     around     the     "  Old 
Sweet  "    and    the    "  Eed     Sweet " 
Springs,  and  in  the   course   of   the 
stream         which 


flows  from  them 
for  several  miles, 
a  brownish-yellow 
deposit  of  traver- 
tine has  accumu- 
lated to  the  depth 
of  at  least  thirty 
feet.  The  spray 
of  Beaver  Dam 
Falls,  about  three 
miles  below  the 
springs,  incrusts 
every  object  in  its 
reach  with  this 
deposit. 

In  California,  all  about  the  shores  of  Lake  Mono,  abundance  of 
beautiful  and   strangely-branched  coralline  forms   are  found,  which 


FIG.  73.— Deposits  from  Carbonated  Springs. 


CHEMICAL   DEPOSITS   IN  LAKES.  79 

have  evidently  been  formed  in  a  somewhat  similar  way.  In  the  region 
of  the  Yellowstone  Park,  deposits  of  travertine  from  waters  of  hot 
springs  running  down  a  steep  incline,  in  a  succession  of  cascades, 
assume  the  most  beautiful  forms,  as  shown  in  the  accompanying  figure, 
taken  from  Hayden. 

Deposits  of  Iron. — Iron  carbonate,  like  lime  carbonate,  is  to  some 
extent  soluble  in  water  containing  carbonic  acid.  Subterranean  waters, 
therefore,  which  always  contain  atmospheric  carbonic  acid,  when  they 
meet  this  carbonate,  will  take  up  a  small  quantity  in  solution.  Such 
waters  are  called  chalybeate.  On  coming  to  the  surface  the  iron  gives 
up  its  carbonic  acid,  is  peroxidized,  becomes  insoluble,  and  is  deposited. 
As  the  presence  of  organic  matter  is  usually  necessary  to  bring  the  iron 
into  a  soluble  condition,  the  full  discussion  of  this  very  interesting  sub- 
ject is  reserved  until  we  take  up  organic  agencies. 

Deposits  of  Silica. — Silica  is  soluble  in  alkaline  waters,  especially  if 
the  waters  be  hot.  Such  waters,  reaching  the  surface  and  cooling,  de- 
posit the  silica  in  great  abundance,  often  at  first  in  a  gelatinous  con- 
dition, but  drying  to  a  white  porous  material  called  siliceous  sinter. 
Examples  of  such  deposits  are  found  in  all  geysers,  as  in  those  of  Ice- 
land, and  in  the  Steamboat  Springs  in  Nevada,  and  especially  in  the 
wonderful  geysers  of  Yellowstone  Park.  Such  deposits  are  confined 
to  volcanic  regions,  the  volcanic  rocks  furnishing  both  the  alkali  and 
the  heat.  We  will  discuss  these  again  under  Igneous  Agencies. 

Deposits  of  Sulphur  and  Gypsum. — Springs  containing  sulphide  of 
hydrogen  (H9S),  usually  called  sulphur-springs,  sometimes  deposit 
sulphur  by  oxidation  of  the  hydrogen  (II,S-|-0=H20-f  S),  and  some- 
times gypsum.  This  latter  deposit  is  caused  by  the  more  complete  oxi- 
dation of  the  sulphide  of  hydrogen,  forming  sulphuric  acid  (H8S-j-4O 
=H2S04),  and  the  reaction  of  this  acid  on  lime  carbonate  held  in  solu- 
tion in  the  same  water. 

Chemical  Deposits  in  Lakes. 

Salt  Lakes  and  Alkaline  Lakes. — Salt  lakes  may  be  formed  either 
— 1.  By  the  isolation  of  a  portion  of  sea-water  in  the  elevation  of  sea- 
bottom  into  land ;  or,  2.  By  indefinite  concentration  of  river-water  in 
a  lake  without  an  outlet.  Thus,  the  Dead  Sea,  Lake  Elton,  and  the 
brine-pools  of  the  Russian  steppes,  are  probably  concentrated  remains 
of  isolated  portions  of  the  sea,*  for  their  waters  are  highly-concen- 
trated mother-liquors  of  sea-water,  having  a  composition  very  similar 
to  the  mother-liquors  of  the  salt-maker.  The  Caspian  Sea,  on  the  other 
hand,  although '  elevated  lake-margins  show  that  much  of  its  waters 
has  dried  away,  is  still  much  fresher  than  sea-water.  This  fact,  to- 

*  Bischof,  Chemical  and  Physical  Geology,  vol.  i,  p.  396. 


80  AQUEOUS  AGENCIES. 

gether  with  the  composition  of  its  waters,  is  usually  supposed  to  indi- 
cate that  it  has  been  formed  by  the  simple  concentration  of  the  waters 
of  a  once  fresh  lake.*  Yet  there  are  some  evidences,  as  we  shall  see 
hereafter,  of  this  sea  having  been  once  connected  with  the  Black  Sea 
and  with  the  Arctic  Ocean.  The  composition  of  the  waters  of  the  Great 
Salt  Lake  of  Utah  would  seem  to  indicate  its  origin  in  the  isolation  of 
sea- water ;  but  there  are  evidences  of  its  once  having  had  an  outlet,  in 
which  case  it  must  have  been  fresh,  or  at  least  brackish,  f 

Alkaline  lakes  can  only  be  formed  by  the  second  way.  Both  salt 
and  alkaline  lakes,  therefore,  may  be  formed  by  indefinite  concentra- 
tion of  river- water  in  a  lake  without  outlet.  Whether  the  one  or  the 
other  is  formed  depends  .on  the  composition  of  the  river-water.  If  al- 
kaline chlorides  predominate,  a  salt  lake  will  be  formed ;  but  if  alkaline 
carbonates,  an  alkaline  lake.  Such  alkaline  lakes  are  found  in  Hun- 
gary, in  Lower  Egypt,  and  in  Persia.  In  our  own  country,  Lake  Mono, 
fifteen  miles  long  and  twelve  miles  wide,  and  Lake  Owen,  of  at  least 
equal  dimensions,  are  examples  of  alkaline  lakes.  The  waters  of  Lake 
Mono  consist  principally  of  a  strong  solution  of  carbonate  of  soda  and 
chloride  of  sodium,  with  a  little  carbonate  of  lime  and  borate  of  soda.  J 

Conditions  of  Salt-Lake  Formation. — Spring  and  river  waters  always 
contain  a  small  quantity  of  saline  matter  derived  from  the  rocks  and 
soils.  Suppose,  then,  we  have  a  lake  supplied  by  rivers :  1.  If  the 
supply  of  water  by  rivers  is  greater  than  the  loss  by  evaporation  from 
the  lake-surface,  then  the  water  will  rise  until,  finding  an  outlet  in  the 
rim  of  the  lake-basin,  it  flows  into  the  sea.  In  this  case  the  lake  will 
remain  fresh,  or  the  quantity  of  saline  matter  will  be  inappreciable. 
But  if,  on  the  other  hand,  the  loss  by  evaporation  is  greater  than  the 
supply  by  rivers,  the  lake  will  decrease  in  extent,  and  therefore  in  evap- 
orating surface,  until  an  equilibrium  is  established.  Now  all  the  saline 
matters  constantly  leached  from  the  earth  accumulate  in  the  lake  with- 
out limit ;  the  lake,  therefore,  must  eventually  become  saturated  with 
saline  matter,  and  afterward  begin  to  deposit  salt.  It  is  evident,  then, 
that  whether  a  lake  is  fresh  or  salt  depends  upon  whether  or  not  it  has 
an  outlet,  and  this  latter  depends  upon  the  relation  of  supply  by  rivers 
to  loss  by  evaporation.  Lakes  are  mostly  fresh,  because  much  more 
water  falls  on  continents  than  evaporates  from  the  same  surface,  the 
excess  running  back  to  the  sea  by  rivers.  It  is  only  in  certain  parts 
of  the  continents,  where  the  climate  is  very  dry,  that  there  is  no  such 

*  Bischof,  Chemical  and  Physical  Geology,  vol  i,  p.  91. 

f  Gilbert,  Wheeler  Report  for  1872,  p.  49. 

%  The  probability  of  Great  Salt  Lake  having  been  produced  by  simple  evaporation  of 
river-water  is  increased  by  the  difference  in  the  composition  of  the  waters  of  lakes  in 
this  general  region.  Where  sedimentary  rocks  prevail,  as  in  Utah,  they  are  salt ;  where 
volcanic  rocks  prevail,  as  about  Mono  and  Owen,  they  are  alkaline. 


CHEMICAL   DEPOSITS  IN   LAKES.  81 

excess.  In  these  regions  alone,  therefore,  can  salt  lakes  exist.  Such 
regions  occur  in  the  interior  of  Asia,  on  the  plateau  of  Mexico,  in  the 
basin  of  Utah,  and  in  several  other  places. 

Even  in  case  a  salt  lake  is  originally  formed  by  the  isolation  of  a 
portion  of  sea-water,  whether  it  remains  a  salt  lake  or  gradually  becomes 
fresh  will  depend  upon  the  conditions  we  have  already  mentioned. 
For  example :  if  the  Mediterranean  should  be  separated  from  the  At- 
lantic at  the  straits  of  Gibraltar,  it  would  not  only  remain  a  salt  lake, 
but  would  diminish  in  area,  and  finally  deposit  salt.  This  we  conclude, 
because  the  water  of  the  Mediterranean  seems  to  be  a  little  more  salt 
than  that  of  the  Atlantic.  If,  on  the  contrary,  the  Black  Sea  were  sepa- 
rated from  the  Mediterranean,  or  the  Baltic  from  the  Atlantic,  or  the 
bay  of  San  Francisco  from  the  Pacific,  the  supply  by  rivers,  in  the  case 
of  these  inland  seas  being  greater  than  their  loss  by  evaporation,  they 
would  rise  until  they  found  an  outlet,  and  then  would  be  gradually 
rinsed  out,  and  become  fresh.  Lake  Champlain  was,  in  very  recent 
geological  time,  an  arm  of  the  sea.  When  first  isolated  it  was  salt.  It 
has  become  fresh  by  this  process. 

Deposits  in  Salt  Lakes. — The  nature  of  the  chemical  deposits  in  salt 
lakes  will  depend  upon  the  manner  in  which  these  lakes  have  been 
formed.  We  will  take  the  simplest  case,  viz.,  that  of  a  lake  formed  by 
the  isolation  of  sea-water,  and  its  concentration  by  evaporation.  In 
this  case  the  substance  first  deposited  would  he^psum  ;  for  this  sub- 
stance is  insoluble  in  a  saturated  brine,  and  therefore  always  deposits 
first  in  the  artificial  evaporation  of  sea-water  in  salt-making.  Upon 
the  gypsum  would  be  deposited  salt.  Meanwhile,  however,  the  rivers 
during  their  flood-season  would  bring  down  sediments.  During  the 
flood-season,  the  supply  of  water  being  greater  than  loss  by  evaporation, 
the  deposit  of  salt  or  gypsum  would  cease ;  while  during  the  dry  season 
the  deposit  of  sediment  would  cease,  and  the  evaporation  being  now  in 
excess,  the  deposit  of  salt  would  recommence.  Thus  the  deposits  in  the 
bottom  of  salt  lakes  probably  consist  of  alternations  of  salt  and  sedi- 
ment, the  whole  underlaid  by  layers  of  gypsum.  These  views  have  been 
confirmed  by  observation.  During  the  dry  season  Lake  Elton  deposits 
annually  a  considerable  layer  of  salt.  Wrells  dug  near  the  margin  of 
this  lake  revealed  a  hundred  alternations  of  salt  and  mud,  the  salt-beds 
being  many  of  them  eight  or  nine  inches  thick.*  Most  of  the  salt  has 
already  deposited ;  for  the  water  of  this  lake  is  an  almost  pure  bittern. 
The  great  predominance  of  chloride  of  magnesium  in  Dead  Sea  water 
shows  that  it  is  a  mother-liquor,  from  which  immense  quantities  of 
common  salt  have  already  been  deposited.  Similar  alternations,  there- 
fore, no  doubt  exist  in  the  bottom  of  this  sea.f  The  Great  Salt  Lake, 

*  Bischof,  Chemical  and  Physical  Geology,  vol.  i,  p.  405.  f  Ibid.,  p.  400. 


82  AQUEOUS   AGENCIES. 

in  Utah,  is  also  a  saturated  brine  depositing  salt,  as  is  proved  by  the 
incrustations  of  salt  about  its  margin  in  dry  seasons ;  but  the  deposit 
has  not  progressed  so  far  in  this  case  as  in  the  preceding.  The  great 
extent  to  which  the  waters  of  this  lake  have  dried  away  and  become 
concentrated  is  further  shown  by  old  lake-margins  far  beyond  the 
limits,  and  several  hundred  feet  above  the  level,  of  the  present  shore- 
line. Similar  phenomena  are  observed  about  other  salt  lakes,  especially 
about  the  Caspian  Sea  (Murchison). 

In  the  case  of  salt  lakes,  either  formed  entirely,  or  modified,  by 
river-water,  the  deposits  are  probably  much  more  complex  and  various 
— sometimes  salt,  sometimes  carbonate  of  lime,  and  sometimes  sulphate 
of  lime.  Immense  deposits,  mostly  of  carbonate  of  lime,  are  found 
about  the  salt  lakes  of  Nevada.  They  form  a  conspicuous  feature  of 
the  scenery  about  Pyramid  Lake. 

Deposits  are  also  sometimes  formed  in  lakes  which  are  not  salt. 
For  example :  the  Solfatara  Lake,  Italy,  is  formed  by  the  accumulation 
of  the  water  from  warm  carbonated  springs,  similar  to  those  of  San 
Filippo  and  San  Vignone.  In  this  lake,  therefore,  deposits  of  traver- 
tine are  forming.  Although  these  deposits  take  place  in  a  lake,  they 
properly  belong  to  deposits  from  springs,  since  they  do  not  take  place 
entirely  by  concentration,  but  partly  also  by  escape  of  carbonic  acid. 

Chemical  Deposits  in  Seas. 

Concerning  these  little  is  known.  It  is  certain,  however,  that  all 
rivers  carry  to  the  sea  carbonate  of  lime_in  solution,  and  some  of  them 
in  considerable  quantities.  There  is  scarcely  any  river-water  which 
contains  less  carbonate  of  lime  than  sea- water;  many  rivers  contain 
four  times  as  much.*  This  carbonate  of  lime  thus  constantly  carried 
into  the  sea  must  eventually  deposit  in  some  form.  Usually,  however, 
sea- water  is  kept  below  the  saturating  point  for  this  substance,  by  its 
constant  withdrawal  by  shells  and  corals,  as  will  be  explained  under 
Organic  Agency.  But  in  shallow  bays  nearly  cut  off  from  the  sea,  or 
in  salt  lagoons  on  the  sea-margin  near  the  mouths  of  rivers  in  dry 
climates,  and  subject  to  occasional  overflows  by  the  sea  and  floodings 
by  rivers,  carbonate  of  lime  and  sulphate  of  lime  may  deposit  by  evapo- 
ration. At  the  mouths  of  many  rivers,  whose  waters  contain  much 
carbonate  of  lime,  as,  for  instance,  the  Rhine,  the  delta  deposit  is 
cemented  into  hard  rock  by  means  of  this  substance.  On  shores  of 
coral  seas,  as  upon  the  Keys  of  Florida,  the  coast  of  the  West  India 
Islands,  and  the  islands  of  the  Pacific,  shore-material  is  consolidated 
into  hard  rock  by  the  same  means.  On  many  shores  in  tropical  regions, 
the  waves,  being  driven  up  on  flat  beaches  far  inland,  leave  sea- water 
inclosed  in  shallow  pools,  which  by  evaporation  give  rise  to  calcareous 

*  Bischof,  Chemical  and  Physical  Geology,  vol.  i,  p.  179. 


INTERIOR   HEAT   OF  THE  EARTH.  83 

deposits  which  are  increased  by  the  frequent  alternate  influx  and  evapo- 
ration of  sea- water.  Conglomerate  rocks  are  thus  forming  at  the  pres- 
ent time  in  the  Canaries  and  many  other  places. 


CHAPTER   III. 
IGNEOUS    AGENCIES. 

THE  agencies  thus  far  considered  tend  to  reduce  the  inequalities  of 
the  earth  by  cutting  down  the  continents  and  filling  up  the  seas.  Their 
final  effect,  if  unopposed,  would  be  to  bring  the  whole  surface  to  one 
level,  and  thus  to  make  the  empire  of  the  sea  universal.  This  is  pre- 
vented by  igneous  agencies,  which  tend,  by  elevation  of  land  and  de- 
pression of  sea-bottoms,  to  increase  the  inequalities  of  the  earth-surface, 
and  thus  to  increase  the  area  and  the  height  of  the  land.  All  the  dif- 
ferent forms  of  igneous  agency  are  connected  with  the  interior  heat  of 
the  earth.  This  must,  therefore,  be  first  considered. 

SECTION  1. — INTERIOR  HEAT  OF  THE  EARTH. 
Stratum  of  Invariable  Temperature. — The  mean  surface  temperature 
of  the  earth  varies  from  80°  at  the  equator  to  nearly  0°  at  the  poles. 
The  rate  of  decrease  in  passing  from  the  equator  to  the  poles  is  not  the 
same  in  all  longitudes ;  the  isotherms,  or  lines  joining  places  of  equal 
mean  temperatures,  are  therefore^  not  parallel  to  the  lines  of  latitude, 
but  quite  irregular.  The  mean  temperature  of  the  whole  earth-surface 
is  about  58°.  There  is  also  in  every  locality  a  daily  and  an  annual 
variation  of  temperature.  As  we  pass  below  the  surface  both  the  daily 
and  annual  variations  become  less,  until  they  cease  altogether.  The 
stratum  of  no  daily  variation  is  but  a  foot  or  two  beneath  the  surface ; 
but  the  stratum  of  no  annual  variation,  or  stratum  of  invariable  tem- 
perature in  temperate  climates,  is  about  sixty  to  seventy  feet  deep.  The 
temperature  of  the  invariable  stratum  is  nearly  the  mean  temperature 
of  the  place.  The  depth  of  the  invariable  stratum  depends  upon  the 
amount  of  annual  variation ;  it  is,  therefore,  least  at  the  equator,  and 
increases  toward  the  poles.  At  the  equator  it  is  only  one  or  two  feet 
beneath  the  surface ;  *  in  middle  latitudes  about  sixty  feet,  and  in  high 
latitudes  probably  more  than  a  hundred  feet.f  It  is,  therefore,  a  sphe- 
roid more  oblate  than  the  earth  itself.  The  temperature  of  the  earth 
everywhere  within  this  spheroid  is  unaffected  by  external  changes. 

*  Humboldt,  Cosmos,  Sabine's  edition,  vol.  5,  p.  165. 

f  In  polar  regions,  or  the  region  of  perpetual  ground-ice,  the  stratum  of  invariable 
temperature  probably  again  rises  nearer  the  surface,  on  account  of  the  property  of  ice  of 
retaining  its  temperature  by  melting. 


84  IGNEOUS  AGENCIES. 

Increasing  Temperature  of  the  Interior  of  the  Earth.— Beneath  the 
invariable  stratum  the  temperature  of  the  earth  everywhere  increases, 
for  all  depths  to  which  it  has  been  penetrated,  at  an  average  rate  of  about 


FIG.  74.  FIG.  75. 

1°  for  every  53  feet.  This  very  important  fact  has  been  determined  by 
numerous  observations  on  the  temperature  of  mines  and  of  Artesian 
wells  in  almost  every  part  of  the  earth.  All  the  facts  thus  far  stated 
are  graphically  illustrated  in  the  accompanying  figure  (Fig.  74),  in 
which  the  line  a  ~b  represents  depth  below  the  surface,  and  the  diverging 
line  c  d  the  increasing  heat ;  m  the  invariable  stratum ;  n  the  line  of  no 
daily  variation ;  the  curves  p  e,  c  0,  o  e,  the  temperatures  in  summer, 
autumn,  and  winter,  respectively ;  the  space  ceo  the  annual  swing  of 
temperature ;  and  the  smaller  curves  meeting  on  the  line  n,  the  daily 
variation  or  swing  of  temperature. 

We  have  given  the  rate  of  increase  as  about  1°  in  53  feet.  It 
varies,  however,  in  different  places,  from  1°  in  30  feet  to  1°  in  90  feet. 
Except  in  the  vicinity  of  volcanic  action,  this  difference  is  probably 
due  to  varying  conductivity  of  the  rocks.  The  lines,  or  rather  surfaces, 
which  join  places  in  the  interior  of  the  earth,  having  equal  tempera- 
tures, may  be  called  isogeotlierms.  If  the  rate  of  increase  were  every- 
where the  same,  the  isogeotherms  would  be  regularly  concentric ;  but, 
as  this  is  not  the  case,  they  are  irregular  surfaces  (Fig.  75),  rising 
nearer  the  earth-surface  and  closing  upon  one  another  where  the  con- 
ductivity is  poor,  and  sinking  deeper  and  separating  where  the  con- 
ductivity is  greater. 

Constitution  of  the  Earth's  Interior. — From  the  facts  given  above 
it  is  probable  that  the  temperature  of  the  interior  of  the  earth  is  very 
great.  A  rate  of  increase  of  1°  for  every  53  feet  would  give  us,  at  the 
depth  of  twenty-five  or  thirty  miles,  a  temperature  sufficient  to  fuse  most 


INTERIOR  HEAT   OF  THE  EARTH.  85 

rocks.  Hence  it  has  been  confidently  concluded  by  many  that  the 
earth,  beneath  a  comparatively  thin  crust  of  thirty  miles,  must  be  liquid. 
A  crust  of  thirty  miles  on  our  globe  is  equivalent  to  a  crust  of  less  than 
one  tenth  of  an  inch  in  a  globe  two  feet  in  diameter.  There  are,  how- 
ever, many  objections  to  this  conclusion.  The  question  of  the  interior 
constitution  of  the. earth  is  one  of  extreme  difficulty  and  complexity, 
and  science  is  not  yet  in  a  position  to  solve  it  completelv.  Neverthe- 
less, it  can  be  proved  that  the  solid  crust  must  be  much  thicker  than  is 
usually  supposed,  if,  indeed,  there  be  any  general  interior  fluid  at  all. 

The  argument  for  the  interior  fluidity  of  the  earth,  beneath  a  crust 
of  only  thirty  miles,  proceeds  upon  two  suppositions,  viz :  1.  That  the 
interior  temperature  increases  at  the  same  rate  for  all  depths  ;  and,  2. 
That  the  fusing -point  of  rocks  is  the  same  for  all  depths.  Now,  neither 
of  these  can  be  true. 

1.  Rate  of  Increase  not  uniform. — Although  we  have  spoken  of  1° 
for  every  30  feet  or  50  feet  or  90  feet,  yet  it  must  not  be  supposed 
that  observation  gives  a  uniform  rate  of  increase  at  any  place.  On  the 
contrary,  the  rate  is  sometimes  faster  and  sometimes  slower,  depending 
on  the  conductivity  of  the  rock  penetrated,  and  on  other  causes  little 
understood.  The  rate  given  is  always  an  average.  In  other  words, 
observation  gives  the  fact  of  increase,  but  not  the  law.  We  are  thus 
thrown  back  on  general  reasoning. 

If  two  bars,  one  a  good  conductor,  like  metal,  and  the  other  a  bad 
conductor,  like  charcoal,  be  heated  red  hot  at  one  end,  and  the  rate  of 
decreasing  temperature — fall  of  heat — toward  the  other  be  observed,  it 
will  be  found  that  the  rate  is  very  rapid  in  the  case  of  the  charcoal,  so 
that  a  temperature  of  60°  is  reached  at  the  distance  of  two  or  three 
inches ;  while  in  the  case  of  the  metal  the  rate  of  decrease  is  much 
slower,  and  60°  is  only  reached  at  a  distance  of  several  feet.  Con- 
versely, the  rate  of  increase,  or  rise,  in  passing  toward  a  source  of  heat, 
is  rapid  in  the  case  of  the  bad  conductor,  and  slow  in  the  case  of  the 
good  conductor.  Now,  the  average  density  of  materials  at  the  surface 
of  the  earth  is  about  2-5,  but  the  average  density  of  the  whole  earth  is 
more  than  5'5  ;  therefore  the  density  of  the  central  portions  must  be 
much  more  than  5'5.  It  has  been  estimated  at  16-27.*  There  can  be 
no  doubt,  therefore,  that  the  density  of  the  earth  increases  toward  the 
center ;  and  as  this  increase  is  probably  largely  the  result  of  pressure, 
it  is  probably  somewhat  regular.  Whatever  be  the  cause,  the  effect 
would  be  to  increase  the  conductivity  for  heat,  and  therefore  to  diminish 
the  rate  of  increasing  temperature.  Thus  it  follows  that,  though  in 
a  homogeneous  globe  the  melting-point  of  rocks  (3,000°)  would  be 
reached  at  the  depth  of  thirty  miles,  yet,  in  a  globe  increasing  in 

*  Cosmos,  vol.  iv,  p.  33. 


86 


IGNEOUS  AGENCIES. 


FIG.  76. 


density  toward  the  center,  we  must  seek  this  temperature  at  a  greater 
depth. 

If  A  B  (Fig.  76),  representing  depth  from  the  surface  S  S,  be  taken 
as  absciss,  and  heat  be  represented  by  ordinates,  then,  in  a  homogene- 
ous earth,  C  D  would  represent  uniform 
increase  of  heat,  and  the  heat  ordinate 
of  3,000°,  m  m,  would  be  reached  at  the 
depth  of  A  m  =  thirty  miles.  But  in  an 
earth  increasing  in  density,  and,  there- 
fore, in  conductivity,  the  rate  would  not 
be  uniform,  but  gradually  decreasing. 
This  would  be  represented,  not  by  a 
straight  line,  C  D,  but  by  a  curved  line, 
C  E;  and  the  ordinate  of  3,000°  would 
not  be  reached  at  thirty  miles,  but  at  a 
much  greater  depth — say  at  m',  of  fifty 
miles. 

2.  Fusing-Point  not  the  same  for  all 
Depths. — Nearly  all  substances  expand 
in  the  act  of  melting,  and  contract  in 
the  act  of  solidifying.  Only  in  a  few  substances,  like  ice,  is  the  re- 
verse true.  Now,  the  fusing  point  of  all  substances  which  expand  in 
the  act  of  fusing  must  be  raised  by  pressure,  since  the  expanding  force 
of  heat,  in  this  case,  must  overcome  not  only  the  cohesion,  but  also  the 
pressure.  That  this  is  true,  has  been  proved  experimentally  for  many 
substances  by  Hopkins.*  But  granite  and  other  rocks  have  been 
proved  to  expand  in  fusing;  therefore  the  fusing-point  of  rocks  is 
raised  by  pressure,  and  must  be  greatly  raised  by  the  inconceivable 
pressure  to  which  they  are  subjected  in  the  interior  of  the  earth.  For 
this  reason,  therefore,  we  must  again  go  deeper  to  find  the  interior. fluid. 
In  the  figure,  m'  is  the  point  where  we  last  -found  the  fusing-point  of 
3,000°.  But  this  is  the  fusing-point  on  the  surface,  or  under  atmos- 
pheric pressure.  The  pressure  of  fifty  miles  of  rock  would  certainly 
greatly  raise  the  fusing-point.  Suppose  iina  thus  raised  to  3,500°  : 
to  find  this  we  must  go  still  deeper,  to  m' ',  perhaps  seventy-five  miles 
in  depth.  But  the  increased  pressure  would  again  raise  the  fusing- 
point  ;  and  thus,  in  this  chase  of  the  increasing  heat  after  the  flying 
fusing-point,  where  the  former  would  overtake  the  latter,  or  whether 
it  would  overtake  it  at  all,  science  is  yet  unable  to  answer. 

From  this  line  of  reasoning,  therefore,  we  conclude  that  the  solid 
crust  of  the  earth  must  be  much  thicker  than  is  usually  supposed,  and 
there  may  be  even  no  interior  liquid  at  all. 


*  American  Journal  cf  Science  and  Art.  II,  vol.  xxxii,  p.  "' 


VOLCANOES.  87 

^ 

Astronomical  Reasons.  —  There  is  another  and  entirely  different 
line  of  reasoning  which  has  led  some  of  the  best  mathematicians  and 
physicists  to  the  same  result.  According  to  the  thin-crust  theory,  the 
earth  is  still  substantially  a  liquid  globe,  and  therefore  under  the  at- 
tractive influence  of  the  sun  and  moon  it  ought  to  behave  like  a  yielding 
liquid.  Now,  according  to  Hopkins,  Thomson,  and  others,  the  earth  in 
all  its  astronomical  relations  behaves  like  a  rigid  solid  —  a  solid  more 
rigid  than  a  solid  globe  of  glass  —  and  the  difference  between  the  be- 
havior of  a  liquid  globe  and  a  solid  globe  could  easily  be  detected  by 
astronomical  phenomena.*  A  complete  exposition  of  the  proof  would 
be  unsuitable  to  an  elementary  work.  Suffice  it  here  to  say  that  the 
force  of  these  arguments  has  led  some  geologists  to  the  conclusion  that 
the  earth  must  be  regarded  as  a  substantially  solid  and  very  rigid  globe  ; 
that  volcanoes  are  openings  into  local  reservoirs  of  liquid,  not  into  a 
general  liquid  interior  —  into  subterranean  fire-lakes,  not  into  an  interior 
fire-sea  ;  and  that,  therefore,  the  theories  of  igneous  phenomena  must 
be  constructed  on  the  basis  of  a  substantially  solid,  not  a  substantially 
liquid,  earth. 

There  are  many  phenomena,  however  —  especially  the  great  lava- 
floods  —  to  be  described  hereafter  and  the  instability  of  the  crust-level 
under  increase  and  decrease  of  weight  by  sedimentation  and  erosion, 
which  seem  to  require  an  unlimited  supply  of  liquid  matter  at  no  great 
distance  beneath  the  surface.  Many  geologists,  therefore,  find  a  com- 
promise in  the  view  that  there  exists  a  liquid  or  semi-liquid  layer^ 
either  universal  or  over  large  areas,  between  the  solid  crust  and  a  solid 
nucleus.  This  is  called  the  sub-crust  layer.  This  seems,  on  the  whole, 
the  most  probable  view.f 

The  interior  heat  of  the  earth  manifests  itself  at  the  surface  in  three 
principal  forms,  viz.,  volcanoes,  earthquakes,  and  gradual  oscillations  of 
Ihe  eartli's  crust. 


SECTION  2.— 

Definition.  —  A  volcano  is  usually  a  conical  mountain,  with  a  funnel- 
shaped,  or  pit-shaped,  or  cup-shaped  opening  at  the  top,  through  which 
are  ejected  materials  of  various  kinds,  always  hot,  and  often  in  a  fused 
condition.  The  activity  of  volcanoes  is  sometimes  constant,  as  in  the 
case  of  Stromboli,  in  Italy,  and  Kilauea,  in  Hawaii,  but  more  commonly 
intermittent,  i.  e.,  having  periods  of  eruption  alternating  with  periods 
of  more  or  less  complete  repose.  Volcanoes  which  have  not  been 
known  to  erupt  during  historic  times  are  said  to  be  extinct.  It  is  im- 
possible, however,  to  draw  the  line  of  distinction  between  active  and 

*  Thomson  has  recently  reaffirmed  these  conclusions  with  still  greater  positiveness.  — 
Nature,  vol.  xiv,  p.  426  ;  American  Journal  of  Science  and  Art,  vol.  xii,  p.  336,  1876. 
f  American  Geologist,  vol.  i,  p.  382,  vol.  ii,  p.   28,  and  vol.  iv,  p.  33. 


88  IGNEOUS  AGENCIES. 

extinct  volcanoes.  Vesuvius,  until  the  great  eruption  which  overthrew 
the  ancient  cities  of  Herculaneum  and  Pompeii,  was  regarded  as  an  ex- 
tinct volcano.  Since  that  time  it  has  been  very  active.  Krakatoa,  after 
a  silence  of  200  years,  burst  out  in  1883  in  the  greatest  eruption  known. 

Size,  Number,  and  Distribution. — Some  volcanoes  are  among  the 
loftiest  mountains  on  our  globe.  Aconcagua,  in  Chili,  is  23,000  feet,  (70- 
topaxi,  in  Peru,  19,660  feet  in  height.  These  volcanic  cones,  however, 
are  situated  on  a  high  plateau ;  their  height,  therefore,  is  not  due  to  vol- 
canic eruptions  entirely.  But  Mauna  Loa,  in  Hawaii,  nearly  14,000  feet, 
and  Mount  Etna,  11,000  feet  high,  seem  to  be  due  entirely,  and  Mount 
Shasta,  California,  14,440  feet,  Rainier,  State  of  Washington,  14,444,  al- 
most entirely  to  this  cause.  The  crater  of  Mauna  Loa  is  two  and  a  half 
miles  across ;  that  of  Kilauea  three  miles  across  and  1,000  feet  deep. 

The  number  of  known  volcanoes,  according  to  Humboldt,  is  407, 
and  of  these  225  are  known  to  have  been  active  in  the  last  160  years. 
The  actual  number  is,  however,  probably  much  greater.  It  has  been 
estimated  that,  in  the  archipelago  about  Borneo  alone,  there  are  900  vol- 
canoes.* The  distribution  of  volcanoes  is  remarkable,  (a.)  They  are 
almost  entirely  confined  to  the  vicinity  of  the  sea.  Two  thirds  of  them 
are  found  on  islands  in  the  midst  of  the  sea,  and  the  remainder,  with 
the  exception  of  a  few  in  the  interior  of  Asia,  are  near  the  sea-coast. 
Those  on  islands  in  the  sea,  probably  commenced,  most  of  them,  at  the 
bottom  of  the  sea,  the  islands  having  been  formed  by  their  agency. 
New  islands  have  been  suddenly  formed  under  the  eye  of  observers  in 
the  Mediterranean  and  in  the  Pacific  Ocean.  The  basin  of  the  Pacific 
is  the  great  theatre  of  volcanic  activity,  nearly  seven  eighths  of  all 
known  volcanoes  being  situated  on  its  coasts  or  on  islands  in  its  midst. 
(b.)  Volcanoes  are,  moreover,  distributed  in  groups  (as  the  Hawaiian 
volcanoes,  the  Mediterranean  volcanoes,  the  Icelandic  volcanoes,  the 
West  Indian  volcanoes,  the  volcanoes  of  Auvergne,  etc.),  or  along  ex- 
tensive lines  as  if  connected  with  a  great  fissure  of  the  earth's  crust. 
The  most  remarkable  linear  series  of  volcanoes  is  that  which  belts  the 
Pacific  coast.  Commencing  with  the  Fuegian  volcanoes  it  runs  along 
the  whole  extent  of  the  Andes,  then  along  the  Cordilleras  of  Mexico, 
the  Rocky  Mountains,  then  along  the  Aleutian  chain  of  islands,  Kamt- 
chatka,  the  Kurile  Islands,  Japan  Islands,  Philippines,  New  Guinea, 
New  Zealand,  to  the  antarctic  volcanoes  Mounts  Erebus  and  Terror, 
thence  back  by  Deception  Island  to  Fuegia  again,  thus  completely  en- 
circling the  globe,  (c.)  Volcanoes  are  generally  formed  in  compara- 
tively recent  strata.  This  seems  to  be  connected  with  their  relation 
to  the  sea ;  for  recent  strata  are  abundant  about  the  sea-coast,  and  the 
most  recent  are  now  forming  in  the  bed  of  the  sea.  The  extinct  vol- 

*  Herschel,  Physical  Geology,  p.  113. 


VOLCANOES.  89 

canoes  of  France  and  Germany  are  in  tertiary  regions.  Possibly  the 
retiring  of  the  sea  has  extinguished  them.  In  the  oldest  strata  vol- 
canic activity  has  apparently  died  out  long  ago. 

Phenomena  of  an  Eruption.—  The  phenomena  of  an  eruption  are  very 
diverse.  Sometimes  there  is  a  gradual  melting  of  the  floor  of  the  crater, 
and  then  a  rising  and  boiling  of  the  liquid  contents  until  they  quietly 
overflow  and  form  immense  streams  of  lava,  extending  fifty  to  sixty 
miles.  After  the  eruption,  the  melted  lava  again  sinks  and  cools,  and 
solidifies,  to  form  the  floor  of  the  crater  until  another  eruption.  This 
is  the  case  with  the  Hawaiian  and  many  other  volcanoes  in  the  South 
Seas.  In  other  cases,  as  in  the  Mediterranean  volcanoes,  and  especially 
in  many  in  the  Indian  Ocean,  the  eruption  is  fearfully  explosive.  In 
such  cases  the  eruption  is  usually  preceded  by  premonitory  earthquakes 
and  sounds  of  subterranean  explosions  ;  then  the  bottom  of  the  crater 
is  blown  out  with  a  violent  explosion,  throwing  huge  rocky  fragments 
to  great  distances,  often  many  miles  ;  then  the  melted  lava  rises  and 
overflows  in  streams  running  down  the  side  of  the  mountain.  The  rise 
and  overflow  of  lava  are  accompanied  with  violent  explosions  of  gas 
which  throw  up  immense  quantities  of  ashes  and  cinders  6,000  and 
even  10,000  feet  above  the  crater.*  The  fine  ashes  from  Krakatoa  is 
said  to  have  been  carrried,  by  the  uprush  of  gas  and  vapors,  to  the 
amazing  height  of  17  miles,  f  In  the  great  eruption  of  Tomboro,  in 
the  island  of  Sumbawa  near  Java,  in  1815,  these  explosions  were  heard 
in  Sumatra,  970  miles  distant.  J  Explosions  of  Krakatoa  were  heard 
2,000  and  even  3,000  miles.4*  The  emission  of  gas  usually  continues 
after  all  other  ejections  cease.  Violent  storms  and  heavy  rain  accom- 
pany the  eruption,  and  when  the  mountain  reaches  into  the  region  of 
perpetual  snow,  as  in  many  of  the  South  American  volcanoes,  the 
fearful  deluges  produced  by  the  sudden  melting  of  the  snows  are  often 
the  most  destructive  phenomenon  connected  with  the  eruption. 

Volcanic  eruptions,  therefore,  may  be  divided  into  two  great  types, 
viz.,  the  quiet  and  the  explosive.  In  the  one,  lava-flows  predominate  ; 
in  the  other,  cinders  and  ashes,  and  steam  and  gas.  The  Hawaiian  vol- 
canoes are  perhaps  the  best  examples  of  the  former,  and  the  Javanese  vol- 
canoes, especially  Krakatoa,  of  the  latter.  The  Mediterranean  and  most 
other  volcanoes  are  mixtures  of  these  two  types  in  varying  proportions. 

The  quantity  of  materials  ejected  during  an  eruption  is  sometimes 
almost  inconceivable.  During  the  great  eruption  of  Tomboro,  already 
mentioned,  ashes  and  cinders  were  ejected  sufficient  to  make  three 
Mont  Blancs,  or  to  cover  the  whole  of  Germany  two  feet  deep.  ||  In 

*  Dana's  Manual,  p.  692.  *  Science,  vol.  iv,  p.  134,  1884. 

+  Judd,  Nature,  vol.  xxxviii,  p.  540,  1888.  ,      [  Herschel,  Physical  Geology,  p.  111. 

J  Lyell,  Principles  of  Geology. 


• 
FERSITY- 


90  IGNEOUS  AGENCIES. 

the  eruption  of  Krakatoa,  August,  1883,  4J  cubic  miles  of  material 
were  blown  into  dust  so  fine  that  it  was  carried  by  the  gas- current  17 
miles  high,  and  some  of  it  remained  suspended  for  two  or  three  years. 
The  lava  which  streamed  from  Skaptar  Jokull,  Iceland,  in  1783,  has 
been  computed  to  be  equivalent  to  about  twenty-one  cubic  miles,  or  to 
the  whole  quantity  of  water  poured  by  the  Nile  into  the  sea  in  one 
year!  These  were,  however,  very  extraordinary  eruptions.  In  the 
greatest  eruptions  of  Vesuvius  the  quantity  of  lava  poured  out  was  not 
more  than  600,000,000  cubic  feet  =  one  square  mile  covered  twenty- 
two  feet  deep.  The  volume  of  lava  poured  out  by  Kilauea,  in  1840,  is 
estimated  by  Dana  as  sufficient  to  cover  one  square  mile  of  surface  800 
feet  deep. 

Great  destruction  of  life  is  often  produced  by  volcanic  eruptions. 
The  overthrow  of  Herculaneum  and  Pompeii  by  ejections  from  Vesu- 
vius is  well  known.  The  great  eruption  of  Skaptar  Jokull  destroyed 
1,300  human  lives  and  150,000  domestic  animals.  The  eruption  of 
Etna,  in  1669,  overwhelmed  fourteen  towns  and  villages.  In  the  prov- 
ince of  Tomboro,  out  of  a  population  of  12,000,  only  twenty-six  persons 
escaped  the  great  eruption  of  1815. 

Monticules. — Eruptions  occur  not  only  from  the  summit-crater,  but 
also  frequently  from  fissures  in  the  side  of  the  mountain.  By  the  im- 
mense upheaving  force  necessary  to  raise  lava  to  the  mouth  of  the 
crater  of  a  lofty  volcano,  the  mountain  is  fissured  by  cracks  radiating 
from  the  crater  in  all  directions.  These  cracks  are  filled  with  lava, 
which  on  hardening  form  radiating  dikes  which  intersect  the  successive 
layers  of  ejections,  and  bind  them  into  a  stronger  mass  (Eig.  79,  p.  94). 
Through  these  fissures  the  principal  streams  of  lava  often  pass.  During 
an  eruption  of  Mauna  Loa,  in  1852,  the  immense  pressure  of  the  lava  in 
the  principal  crater  fissured  the  side  of  the  mountain,  and  a  fiery  fount- 
ain of  liquid  lava,  1,000  feet  wide,  was  projected  upward  through  the 
fissure  to  the  height  of  700  feet,  and  continued  to  play  for  several  days. 
Upon  these  fissures  subordinate  craters,  and  finally  cones,  are  formed. 
These  subordinate  cones  about  the  base,  and  upon  the  slopes  of  the 
principal  cone,  are  called  monticules  or  hornitos.  There  are  about  600 
monticules  on  Etna — one  of  them  over  700  feet  high  (Jukes). 

Materials  erupted. — As  we  have  already  stated,  the  materials  erupted 
are  stones,  lava-streams,  cinders,  ashes,  and  gases. 

Stones. — In  explosive  eruptions  the  solid  floor  of  the  crater  is  often 
blown  out  with  violence,  and  rock-fragments,  sometimes  of  vast  size, 
are  thrown  to  great  distances. 

Lava. — the  term  lava  is  applied  to  the  liquid  matter  poured  from  a 
volcano  during  eruption,  and  also  to  the  same  when  it  has  hardened 
into  rock. 

Liquidity  of  Lava. — At  the  time  of  eruption  the  liquidity  of  lava 


VOLCANOES.  91 

varies  very  much,  depending  partly  upon  the  heat,  partly  on  the  fusi- 
bility of  the  material,  and  partly  upon  the  kind  of  fusion.  In  the 
Hawaiian  volcanoes  the  lava  is  a  melted  glass  almost  as  thin  as  honey. 
In  Kilauea  this  lava  is  often  thrown  into  the  air  by  the  bursting  of  gas- 
bubbles,  and  drawn  out  into  long  threads  like  spun  glass,  which  is  car- 
ried by  the  winds,  and  collects  in  places  as  a  soft,  brownish,  towy  mass, 
called  "  Petes  hair." 

Physical  Conditions  of  Lava. — Completely  fused  lava,  when  cooled 
rapidly,  forms  volcanic  slag  or  volcanic  glass  (obsidian) ;  but  if  cooled 
slowly,  so  that  the  several  minerals  of  which  it  is  composed  have  time 
to  separate  and  crystallize,  forms  stony  lava.  If  it  is  full  of  gas-bubbles 
(rock-froth),  and  hardens  in  this  condition,  it  forms  vesicular  or  scori- 
aceous  lava.  If  the  quantity  of  gas  and  steam  be  very  great,  the  whole 
liquid  mass  may  swell  into  a  rock-froth,  which  rises  to  the  lip  of  the 
crater,  and  outpours  much  as  porter  or  ale  from  a  bottle  when  the  cork 
is  drawn.  Or  the  rock-froth  may  be  thrown  violently  into  the  air,  and, 
hardening  there,  may  fall  again  in  cindery  or  scoriaceous  masses ;  or, 
thrown  with  still  greater  violence,  the  rock-froth  may  be  broken  into 
fine  rock-spray,  and  fall  as  volcanic  sand  and  ashes.  Ashes,  when  con- 
solidated by  time  and  percolating  water,  or  when  deposited  in  water 
form  tufa.  Thus,  there  are  four  physical  conditions  in  which  we  find 
lava — viz.,  stony,  glassy,  scoriaceous,  and  tufaceous. 

Again,  the  liquidity  of  lava  and  its  character  depend  much  on  the 
kind  of  fusion.  Daubree  has  shown  that  all  siliceous  rocks  and  glass 
mixtures,  in  the  presence  of  superheated  water  even  in  small  quantities, 
and  under  pressure,  will  become  more  or  less  liquid,  at  temperatures  far 
below  that  necessary  to  produce  true  fusion.  At  400°  Fahr.,  such  rocks 
become  pasty,  at  800°  completely  liquid.  The  same  change  takes 
place  at  even  lower  temperatures  if  a  little  alkali  be  present.  To  dis- 
tinguish this  liquidity  from  that  of  true  igneous  fusion,  which  requires 
a  temperature  of  2,500°  to  3,000°,  it  has  been  called  aqueo-igneous  or 
hydrothermal  fusion.  Now,  very  much  lava  at  the  time  of  eruption  is 
in  this  condition.  Such  lava,  when  the  pressure  is  suddenly  removed  by 
breaking  up  of  the  floor  of  the  crater,  and  the  contained  water  suddenly 
changed  into  steam,  is  blown  into  the  finest  dust,  which  is  then  carried 
to  great  height  by  the  out-rushing  steam,  and  falls  again  as  volcanic 
ashes,  which  may  consolidate  into  tufa.  If  the  heat  be  not  sufficient  to 
produce  complete  aqueo-igneous  fusion,  the  lava  is  outpoured  as  a  kind 
of  rock-broth,  consisting  of  unfused  particles  in  a  semif used  mass,  which 
concretes  into  an  earthy  kind  of  rock.  Or  the  material  may  pour  out 
only  as  hot  mud,  which  concretes  into  a  kind  of  tufa.  In  fact,  every 
variety  of  fusion  and  semif usion,  depending  on  the  degree  of  heat  and  the 
quantity  of  water,  may  be  traced,  from  perfect  igneous  fusion  through 
various  grades  of  aqueo-igneous  fusion,  to  the  condition  of  hot  mud. 


92  IGNEOUS  AGENCIES. 

It  is  evident  that,  of  the  two  kinds  of  eruption  mentioned  above, 
the  quiet  type  is  characterized  by  igneous  fnsion,  the  explosive  type  by 
aqueo-igneous  fusion.  In  the  former  the  heat  is  great,  but  the  amount 
of  water  is  small ;  while  in  the  latter  the  heat  is  less,  but  the  amount 
of  water  far  greater. 

The  rapidity  of  the  flow  of  a  lava-strearn  depends  on  its  fluidity.  In 
the  Hawaiian  volcanoes  the  lava,  where  it  issues  from  the  crater,  has 
been  seen  to  flow  with  a  velocity  of  fifteen  miles  an  hour;  while 
Vesuvian  lava  seldom  flows  at  a  rate  of  more  than  two  or  three  miles 
an  hour.  Lava,  like  glass,  passes  through  various  grades  of  viscous 
fluidity  in  cooling.  It  gradually  becomes  so  stiff  that  it  may  flow  only 
a  few  feet  per  day.  The  froth  or  scum  which  covers  the  surface  of  a 
lava-stream  quickly  cools  and  hardens  into  a  crust  of  vesicular  lava, 
which  may  even  be  walked  upon  while  the  interior  is  still  flowing 
beneath.  In  this  way  are  often  formed  long  galleries.  Also  the  run- 
ning together  of  the  contained  gas-bubbles  and  steam-bubbles  forms 
huge  blisters  in  the  viscous  mass,  which,  on  hardening,  form  cavities 
often  of  great  size.  Thus,  recent  lavas  have  often  a  cavernous  and 
galleried  structure  (page  76). 

'  Classification  of  \&X2&.-^ineralogicall/y,  lava  consists  essentially 
of  feldspar,  augite,  and  magnetite,  either  intimately  mixed,  as  in  glassy 
lava,  or  aggregated  in  more  or  less  distinct  particles  or  crystals,  as  in  the 
stony  varieties.  Now,  feldspar  is  a  light-colored  mineral,  having  a  spe- 
cific gravity  of  about  2*5,  while  augite  and  magnetite  are  usually  very 
dark-colored  minerals,  having  specific  gravities  of  about  3 -5  to  5.  It 
is  evident,  therefore,  that  in  proportion  as  feldspar  predominates,  the 
lava  is  lighter  colored  and  of  less  specific  gravity ;  and  in  proportion 
as  augite  and  magnetite  predominate,  the  rock  is  darker  and  heavier. 
Chemically,  feldspar  is  a  silicate  of  alumina  and  alkali,  with  excess  of 
silica  (acid  silicate).  The  alkali  may  be  either  potash,  and  then  it  is 
called  potash  feldspar,  or  orthoclase ;  or  else  it  is  soda  and  lime,  and 
then  it  is  called  soda-lime  feldspar,  or  plagioclase.  Of  these  two  the 
former  is  the  more  acid.  Augite  is  a  silicate  of  lime,  magnesia,  and 
iron,  with  excess  of  base  (basic  silicate).  Therefore,  lava  may  be  di- 
vided into  two  classes — acidic  lavas  arid  basic  lavas.  In  the  former, 
feldspar  predominates,  in  the  latter  augite.  Moreover,  in  the  one  the 
form  of  feldspar  is  orthoclase,  in  the  other  plagioclase.  Further,  it  is 
seen  that  all  lavas  are  multiple  silicates,  like  glass  :  they  are,  therefore, 
true  glass-mixtures.  Now,  the  acidic  lavas  are  a  more  difficultly  fusi- 
ble, the  basic  lavas  a  more  easily  fusible  glass-mixture.  Either  of 
these  two  kinds  of  lava  may  exist  in  any  of  the  conditions  mentioned 
above — viz.,  as  stony,  glassy,  vesicular,  or  tufaceous  lava.  Trachyte  is 
an  example  of  acidic  lava,  and  basalt  of  basic  lava  in  a  stony  condition. 
Pumice  is  a  peculiar  vesicular  variety  of  feldspathic  lava. 


VOLCANOES.  93 

It  is  highly  probable  that  the  fusion  and  subsequent  cooling  of 
granite,  or  gneiss,  or  even  of  the  purer  varieties  of  mixed  sandstones 
and  clays,  would  make  a  trachytic  lava ;  while  the  fusion  and  cooling  of 
impure  slates  and  shales  and  limestones  would  produce  basaltic  lava. 

Gas,  Smoke,  and  Flame. — The  gases  emitted  by  volcanoes  are  princi- 
pally steam,  sulphurous  vapor  (S  and  S02),  hydrochloric  acid,  and  car- 
bonic acid.  By  far  the  most  abundant  of  these  is  steam.  In  violent, 
explosive  eruptions,  which  eject  principally  cinders  and  ashes,  it  is  prob- 
able that  water,  mostly  in  the  form  of  steam,  is  one  of  the  most  abun- 
dant of  all  the  ejected  materials.  In  quiet  lava-eruptions,  like  those 
of  the  Hawaiian  volcanoes,  the  quantity  of  steam  and  gases  is  small. 
It  is  worthy  of  notice,  in  connection  with  the  position  of  volcanoes 
near  the  sea,  that  the  gases  ejected  are  such  as  might  be  formed  from 
sea-water  and  from  limestone.  The  so-called  smoke  and  flame  of  vol- 
canoes have  no  connection  with  combustion.  The  condensed  vapors 
and  the  ashes  suspended  in  the  air,  often  in  such  quantities  as  to  make 
midnight-darkness  at  high  noon,  form  the  smoke ;  and  the  red  glare 
of  the  same,  reflecting  the  light  from  the  incandescent  lava  beneath, 
forms  the  apparent  flame. 

All  volcanic  ejections,  except  the  gases,  accumulate  about  the  crater, 
and  continue  to  increase  with  every  successive  eruption,  forming  a  sort 
of  stratified  deposit.  Sometimes  the  cone  is  made  up  of  successive 
layers  of  lava,  as  in  Hawaiian  volcanoes ;  sometimes  it  is  made  up  of 
successive  layers  of  cinders  or  tufa ;  sometimes  of  alternate  layers  of 
lava  and  tufa.  Stratified  materials  of  this  kind,  however,  can  not 
be  confounded  with  those  produced  by  the  action  of  water.  In  the 
former  case  the  stratification  is  not  the  result  of  the  sorting  of  the  ma- 
terials. 

Kinds  of  Volcanic  Cones. — Volcanic  cones  and  craters  have  been 
divided  into  two  kinds — viz.,  cones  of  elevation  and  cones  of  eruption. 
A  cone  of  elevation  is  formed  by  interior  forces  lifting  the  crust  of  the 
earth  at  a  particular  point  until  the  latter  breaks  and  forms  a  crater, 
through  which  eruptions  take  place.  It  is  an  earth-Mister  which 
swells  and  breaks  at  the  top.  A  cone  of  eruption,  on  the  other  hand,  is 
formed  by  the  accumulation  around  a  crater  of  its  own  ejection.  There 
has  been  much  discussion  among  physical  geologists  as  to  whether 
existing  volcanic  cones  are  formed  mostly  by  the  one  method  or  the 
other.  We  will  not  enter  into  this  discussion.  It  seems  probable, 
however,  that  most  cones  are  principally  cones  of  eruption,  although 
their  height  and  size  have  been  increased  somewhat  also  by  elevating 
forces. 

Mode  of  Formation  of  a  Volcanic  Cone. — A  volcano  commences— 1. 
As  a  simple  opening  in  the  earth's  crust,  in  most  cases  with  little  or  no 
elevation.  Through  this  opening  or  crater  are  ejected,  from  time  to 


IGNEOUS  AGENCIES. 


time,  lava,  cinders,  ashes,  etc.,  which  accumulate  immediately  about  the 
crater,  and  continue  to  increase,  by  successive  layers,  with  every  erup- 


B 


FIG.  77.— Section  across  Hawaii. 

tion.  Ejections  of  pure  lava,  particularly  if  the  lava  is  very  fluid,  form 
a  cone  of  broad  base  and  low  inclination.  This  is  the  case  with  the 
Pacific  volcanoes.  Fig.  77  is  a  section  through  Hawaii,  showing  the 
slope  of  the  pure  lava-cones  of  Mauna  Loa  (Z),  nearly  14,000  feet 

high,  and  of  Mauna  Kea  (K ).  Tufa- 
cones  and  cinder-cones  (Fig.  78)  take 
a  much  higher  angle  of  slope.  2. 
With  every  eruption  the  powerful 
internal  forces  fissure  the  mountain, 
in  lines  radiating  from  the  crater. 
These  fissures  are  filled  with  liquid 
lava,  which,  on  hardening,  forms 
radiating  dikes,  intersecting  the  layers  of  ejections,  and  binding  them 
into  a  more  solid  mass.  Fig.  79  shows  how  these  dikes,  rendered 


FIG.  78.— Section  of  Cinder-Cone. 


PIG.  79.— Dikes  at  the  Base  of  the  Serra  del  Solfizio,  Etna. 


VOLCANOES. 


95 


more  visible  by  erosion,  intersect  the  strata.  3.  After  a  time,  when 
the  mountain  has  grown  to  considerable  height,  the  force  necessary 
to  raise  liquid  lava  to  the  lip  of  the  crater  becomes  so  great  that 
it  breaks  in  preference  through  the  fissured  sides  of  the  mountain. 
The  secondary  craters  thus  formed  immediately  commence  to  make 
accumulations  around  themselves,  and  thus  form  secondary  cones  (Fig. 
80,  c'),  or  monticules,  about  the  base  and  on  the  sides  of  the  primary 


FIG.  80.— Section  of  Volcano,  showing  Monticules. 

cone.  If  a  secondary  cone  becomes  extinct,  it  is  finally  buried  (Fig. 
80,  c")  in  the  layers  of  the  primary  cone.  4.  Finally,  in  volcanoes  of 
the  explosive  type,  during  great  eruptions  the  whole  top  of  the  mount- 
ain is  often  blown  off,  and  in  volcanoes  of  the  quieter  type  is  melted 
and  falls  in — in  either  case  forming  an  immense  crater,  within  which,  by 
subsequent  eruptions,  another  smaller  cone  of  eruption  is  built  up,  and 
in  this  latter  often  a  still  smaller  cone  is  again  built.  This  cone-within- 
cone  structure  is  well  illustrated  by  the  present  condition,  and  still 
better  by  the  history,  of  Vesuvius.  Vesuvius  is  a  double-peaked 


FIG.  81.— Section  of  Vesuvius  and  Mount  Somma. 

mountain,  with  a  deep,  semicircular  valley  between  the  peaks.  The 
present  active  cone  of  Vesuvius  is  encircled  by  a  rampart,  very  high 
on  one  side,  and  called  Mount  Somma,  but  traceable  to  some  degree  all 
around,  and  having  the  same  structure  as  Vesuvius  itself.  This  ram- 
part is  the  remains  of  a  great  crater,  many  miles  in  diameter.  Fig.  81 
is  an  ideal  section  through  Mount  Somma  ($),  and  Vesuvius  (  V).  8' 
is  the  almost  obliterated  remains  of  the  old  crater  on  the  other  side. 
This  is  further  and  beautifully  illustrated  by  the  history  of  this  mount- 
ain, which  records  the  repeated  destruction  and  rebuilding  of  these 
cones  within  cones.  Fig.  82  is  an  outline  of  Vesuvius  as  it  existed  in 
1756 ;  *  S  is  Mount  Somma. 

*  Scrope,  Philosophical  Magazine,  vol.  xiv,  p.  139. 


96 


IGNEOUS  AGENCIES. 


Many  other  volcanoes  are  known  which  have  similar  circular  ram- 
parts made  up  of  layers  of  volcanic  ejections.    One  of  the  most  remark- 


FIG.  82.— Mount  Vesuvius  in  1756  (after  Scrope). 

able  of  these  is  Barren  Island,  in  the  Bay  of  Bengal  (Fig.  83).  The 
difference  between  this  and  Vesuvius  is,  that  the  circle  is  more  com- 
plete.* 


Fio.  83.— Section  across  Barren  Island  (after  Mallett):  si,  sea-level.    The  dotted  line  is  added  to 
show  the  supposed  former  condition. 

Comparison  between  a  Volcanic  Cone  and  an  Exogenous  Tree.— It 
is  evident,  then,  that  a  cone  of  eruption  grows  by  layers  successively 
applied  on  the  outside.  Both  in  structure  and  growth  it  may,  there- 
fore, be  compared  to  an  exogenous  tree :  1.  As  the  sap  ascends 
through  the  center  of  the  shoot  and  descends  on  the  outside,  forming 
layers  of  wood,  one  outside  of  the  other,  increasing 
every  year  the  height  and  the  diameter  of  the  tree ;  so 
in  a  volcano  lava  ascends  through  the  center  and  pours 
over  the  outside,  forming  also  successive  layers,  in- 
creasing both  the  diameter  and  the  height.  2.  As  a 
cross-section  of  a  tree  shows  concentric  rings  around 
(Fig.  84)  a  central  pith,  and  is  traversed  \>y  pith-rays  ; 
so  a  cross-section  of  a  volcano  would  show  a  central  crater,  with  con- 
centric layers,  traversed  by  radiating  dikes.  3.  As  on  the  pith-rays, 
where  they  emerge  upon  the  surface,  arise  luds,  which  grow  in  a  man- 
ner similar  to  the  trunk ;  so  on  the  radiating  dikes  are  formed  monti- 

*  Medlicot  and  Blandford,  Manual  of  Geology  of  India,  p.  736. 


FIG.  84. 


THEORY   OF   VOLCANOES.  97 

cules,  which  grow  like  the  principal  cone.  If  buds  die,  they  are  cov- 
ered up  in  the  annual  layers  of  the  trunk ;  so,  in  like  manner,  extinct 
monticules  are  buried  in  the  layers  of  the  principal  cone. 

Estimate  of  the  Age  of  Volcanoes. — The  age  of  exogenous  trees,  as 
is  well  known,  may  be  estimated  by  counting  the  annual  rings.  The 
age  of  volcanoes  can  not  be  estimated  accurately  in  a  similar  manner  : 
1.  Because  the  overflows  are  not  regularly  periodical;  2.  Because  in 
the  case  of  lava-overflows  it  requires  many  overflows  to  make  one 
complete  layer ;  and,  3.  Because  it  is  impossible  to  make  a  complete 
section  of  the  mountain.  Nevertheless,  Nature  gives  us  partial  sec- 
tions, which  reveal  an  almost  incalculable  antiquity.  Thus,  the  Val  de 
Bove,  of  Etna  (a  huge  valley  reaching  from  near  the  summit  to  the 
foot,  and  probably  formed  by  an  ingulf ment  of  a  portion  of  the  mount- 
ain), gives  a  perpendicular  section  into  the  heart  of  the  mountain 
3,000  feet  deep.  Throughout  the  whole  of  this  section  the  mountain 
is  composed  entirely  of  layers  of  lava  and  cinders.  It  is  almost  cer- 
tain, therefore,  that  the  whole  mountain  to  its  very  base,  11,000  feet, 
is  similarly  composed.  That  the  time  necessary  to  accumulate  this  im- 
mense pile,  11,000  feet  high  and  ninety  miles  in  circumference  at  the 
base,  was  almost  inconceivably  great,  is  shown  by  the  fact  that  Etna 
had  already  attained  very  nearly  its  present  size  and  shape  2,500  years 
ago,  when  it  was  observed  by  the  early  Greek  writers.  The  lava-stream 
which  stopped  the  Carthaginians  in  their  march  against  Syracuse,  396 
years  before  Christ,  may  still  be  seen  at  the  surface,  not  yet  covered  by 
subsequent  eruptions.  And  yet  Etna  belongs  to  the  most  recent  geo- 
logical epoch,  for  it  has  broken  through,  and  is  built  upon,  the  newer 
tertiary  strata. 

Theory  of  Volcanoes. 

In  the  theory  of  volcanoes  there  are  two  things  to  be  accounted  for, 
viz. :  1.  The  force  necessary  to  raise  melted  lava  to  the  lips  of  the  crater, 
and  even  to  project  it  with  violence  high  into  the  air;  2.  The  heat 
necessary  to  fuse  rocks  and  form  lava. 

Fo*rce. — The  specific  gravity  of  lava  being  about  2-5  to  3,  it  would 
require  the  pressure  of  one  atmosphere,  or  fifteen  pounds  to  the  square 
inch,  for  every  eleven  or  twelve  feet  of  vertical  elevation  of  the  liquid 
mass.  The  following  table  gives  the  pressure  in  atmospheres  for  four 
well-known  volcanoes,  assuming  the  point  of  hydrostatic  equilibrium 
to  be  at  the  sea-level : 


NAME. 

Height. 

Pressure  in  atmospheres. 

Vesuvius  

3,900  feet 

325 

Etna  

11,000     " 

920 

Mauua  Loa 

13,800     " 

1,150 

Cotopaxi  

19,660     " 

1,638 

98  IGNEOUS  AGENCIES. 

The  lava  is  often,  however,  in  a  frothy  or  vesicular  condition.  In  such 
cases  the  pressure  necessary  to  produce  overflow  would  be  much  less. 
But,  on  the  other  hand,  the  force  in  most  cases  is  not  only  sufficient  to 
lift  lava  to  the  top  of  the  crater,  but  to  project  it  thousands  of  feet  in 
the  air.  A  rock-mass  of  over  2,700  cubic  feet  was  projected  from  the 
crater  of  Cotopaxi  to  a  distance  of  nine  miles  (Lyell).  The  agent  of 
this  prodigious  force  is  evidently  gas  and  vapors,  especially  steam.  The 
great  quantity  of  steam  issuing  from  all  volcanoes,  but  especially  from 
those  of  the  explosive  type,  is  sufficient  proof.  Thus  far  theorists  gen- 
erally agree,  but  from  this  point  opinions  diverge  into  the  most  oppo- 
site directions. 

The  Heat. — There  are  many  and  diverse  opinions  as  to  the  source  of 
the  heat  associated  with  volcanic  eruptions.  Two  prominent  views, 
however,  may  be  said  to  divide  geologists.  According  to  the  one,  the 
heat  is  the  remains  of  the  primal  heat  of  the  once  universally  incandes- 
cent earth ;  according  to  the  other,  the  heat  is  produced  by  chemical 
or  mechanical  action.  According  to  the  former,  the  heat  is  general,  and 
only  the  access  of  water  is  local ;  according  to  the  latter,  both  the  heat 
and  the  access  of  water  are  local.  According  to  the  former,  volcanoes 
are  openings  through  the  comparatively  thin  crust,  revealing  the  uni- 
versal interior  fluid  ;  according  to  the  latter,  they  are  openings  into 
isolated  interior  lakes  of  molten  matter.  The  former  may  be  called  the 
"  interior  fluidity  "  theory ;  the  latter  divides  into  two  branches,  whicli 
may  be  called  respectively  the  "  chemical  "  and  the  "  mechanical "  the- 
ory. In  all,  access  of  water  to  the  hot  interior  furnishes  the  force. 

Internal  Fluidity  Theory. — This  theory  supposes  that  the  earth,  from 
its  original  incandescent  condition,  slowly  cooled  and  formed  a  surface- 
crust  ;  that  this  surface-crust,  though  ever  thickening  by  additions  to 
its  interior  surface,  is  still  comparatively  very  thin,  and  beneath  it  is 
still  the  universal  incandescent  liquid ;  that  by  movements  of  the  sur- 
face the  solid  crust  is  fissured,  and  water  from  the  sea  or  from  other 
sources  finds  its  way  to  the  incandescent  liquid  mass,  and  develops 
elastic  force  sufficient  to  produce  eruption. 

By  this  view  the  focus  of  volcanoes  is  situated  at  the  lower  limit  of 
the  solid  crust.  The  theory  seems  clear  and  simple  enough,  but  when 
closely  examined  there  are  many  difficulties  in  the  way  of  its  accept- 
ance. 

Objections. — The  objections  to  this  view  are  :  1.  That  the  crust,  as 
already  shown,  must  be  far  thicker  than  this  theory  requires,  probably 
hundreds  of  miles  thick,  if,  indeed,  there  be  any  general  liquid  interior 
at  all ;  but  volcanoes  are  evidently  very  superficial  phenomena.  Under 
the  pressure  of  this  difficulty  these  theorists  have  been  driven  to  the 
acknowledgment  of  local  thinnings  of  the  solid  crust  in  the  region  of 
volcanoes. 


THEORY   OF   VOLCANOES.  99 

2.  Pressure  on  a  general  interior  liquid  from  any  cause  at  any  place 
would,  by  the  law  of  hydrostatics,  be  transmitted  equally  to  every  part 
of  the  crust,  which  would,  therefore,  yield  at  the  weakest  point,  wher- 
ever that  may  be,  even  though  it  be  on  the  opposite  side  of  the  globe ; 
but  the  force  of  volcanic  eruption  is  evidently  just  beneath  the  volcano. 

3.  Volcanoes  belonging  to  the  same  group,  and  therefore  near  to- 
gether, often  erupt  independently,  as  if  each  had  its  own  reservoir  of 
liquid  matter.     The  pressure  of  these  two  objections  has  driven  many 
to  the  admission  of  a  sort  of  honey -combed  remains  of  the  interior 
liquid  inclosed  in  the  solid  crust,  and  now  isolated  both  from  the  inte- 
rior liquid  and  from  each  other. 

4.  There  is  a  limit  to  the  descent  of  water  into  the  interior  of  the 
earth ;  gravity  urges   it    downward,  but   the   interior  heat   drives   it 
back.     The  limit,  therefore,  will   be  where  these  two  balance  each 
other,  i.  e.,  where  the  elastic  force  of  steam  is  equal  to  the  superincum- 
bent column  of  water.     We  will  call  this  point  the  limit  of  volcanic 
waters.     It  is  evident  that  when  water  was  first  condensed  on  the  cool- 
ing earth,  this  limit  was  at  the  surface :  water  could  not  penetrate  at 
all.     As  the  earth  cooled,  this  limit  became  deeper  and  deeper  ;  and,  if 
the  earth  became  perfectly  cool  to  the  center,  there  is  little  doubt  that 
the  whole  of  the  water  on  the  earth  would  be  absorbed.     This  is  per- 
haps the  case  with  the  moon  now. 

Now,  it  seems  probable  that  at  the  limit  of  volcanic  water  the  in- 
terior heat  of  the  earth,  increasing  at  the  rate  of  1°  for  every  fifty  feet, 
would  be  far  short  of  the  temperature  necessary  for  igneous  fusion  of 
rocks.  Again,  the  elastic  force  necessary  to  sustain  the  superincum- 
bent water  would  by  no  means  be  sufficient  to  break  up  the  crust  of 
the  earth,  or  raise  melted  lava  to  the  surface. 

But  we  will  not  pursue  this  subject,  as  it  is  too  complex  to  be  yet 
solved  by  science.  We  rely,  therefore,  on  the  first  three  objections. 

Chemical  Theory. — Whether  or  not  the  earth  consist  of  solid  crust 
covering  an  interior  liquid,  it  almost  certainly  consists  of  an  oxidized 
crust  covering  an  unoxidized  interior.  (Now,  the  oxidizing  agents  are 
water  and  air,  and  therefore  the  limit  of  the  oxidized  crust  is  the  limit 
of  volcanic  watej^  Therefore,  the  oxidizing  agent  and  the  unoxidized 
material  are  in  close  proximity,  and  the  former  ever  encroaching  on  the 
latter,  and  therefore  liable  at  any  moment  to  set  up  chemical  action, 
the  intensity  of  which  would  vary  with  the  nature  of  the  material.  If 
the  action  be  intense,  heat  may  be  formed  sufficient  to  fuse  the  rocks 
and  to  develop  elastic  force  necessary  to  produce  eruption. 

In  this  general  form,  the  chemical  theory  seems  plausible,  but  many 
have  attempted  to  give  it  more  definiteness,  and  to  explain  the  special 
forms  of  oxidization  which  cause  volcanoes.  The  most  celebrated  of 
these  definite  forms  is  that  of  Sir  Humphry  Davy,  who  attributed  it  to 


100  IGNEOUS  AGENCIES. 

the  contact  of  water  with  metallic  potassium,  sodium,  calcium,  and 
magnesium,  in  the  interior  of  the  earth.  In  such  definite  forms  the 
theory  seems  far  too"  hypothetical. 

Recent  Theories.  —  1.  Aqueo-igneous  Theory. — Accumulation  of 
sediment  on  sea-bottoms  would  necessarily  produce  corresponding  rise 
of  isogeotherms,  and  thus  the  interior  heat  of  the  earth  would  invade 
the  sediments  with  their  contained  waters.  The  lower  portion  of  sedi- 
ments 10,000  feet  thick  would  be  raised  to  a  temperature  of  about  260° 
Fahr.,  and  of  40,000  feet  thick  (sediments  of  this  thickness  and  more  are 
known)  to  that  of  860°.  This  temperature,  or  even  a  less  temperature 
if  alkali  be  present,  would  be  sufficient  in  the  presence  of  the  contained 
water  of  the  sediments  to  produce  complete  aqueo-igneous  fusion,  and 
probably  to  develop  elastic  force  sufficient  to  produce  eruption.  This 
view  was  first  brought  forward  by  John  Herschel.  Observe  that  this 
temperature  and  the  corresponding  force  would  be  gradually  developed 
as  the  accumulation  progressed,  until  sufficient  to  produce  these  effects. 
Observe,  again,  that  in  this  case  the  water  does  not  seek  the  heat  by 
descending  (the  difficulties  in  the  way  of  this  we  have  already  seen), 
but  the  heat  seeks  the  already  imprisoned  water  by  ascending. 

It  seems  very  probable  that  cases  of  eruption  of  hot  mud  and  of 
aqueo-igneously  fused  lavas  may  be  accounted  for  in  this  way,  but  the 
temperature  would  not  be  sufficient  to  account  for  true  igneous  fusion. 

2.  Mechanical   Theory. — As  we  shall  explain  hereafter   (p.  263), 
there  is  much  reason  to  believe  that  the  interior  of  the  earth  is  con- 
tracting more  rapidly  than  the  exterior,  and  that  the  exterior  is  thus 
necessarily  thrust  upon  itself  by  irresistible  horizontal  pressure.     Ac- 
cording to  Mr.  Mallet,  the  crushing  of  the  rocky  crust  in  places  under 
this  pressure  develops  heat  sufficient  to  fuse  the  rocks,  and  to  produce 
eruption.     But  it  is  at  least  doubtful  whether  the  heat  thus  generated 
would  alone  be  sufficient  for  this  purpose. 

3.  Issuing  of  Superheated  Gases. — Rev.  0.  Fisher  has  advanced  a 
view  which  deserves  attention.     He  thinks  volcanoes  are  vents  through 
which  issue  from  the  earth's  interior  superheated  steam  and  gases, 
melting  the  rocks  in  their  course  and  ejecting  them  by  their  press- 
ure.    According  to  this  view,  the  water  is  not  derived  from  the  sur- 
face, but  is  original  and  constituent.      This  view  is  independent  of 
the  condition  of  the  earth's  interior,  whether  solid  or  liquid ;  for  a 
temperature  which  would  permit  solidity  at  great  depths  would  pro- 
duce fusion  under  less  pressure  near  the  surface.*     The  sun  may  be 
regarded  as  a  globe  in  an  earlier  and  more  active  stage  of  vulcanism. 
From  its  interior  gases  are  seen  to  issue  in  great  quantity,  and  almost 
constantly. 

*  Cambridge  Philosophical  Society,  1875. 


GEYSERS.  101 

4.  PrestwicWs  Theory. — If  we  assume  the  existence  of  a  sub-crust 
layer  of  liquid  matter,  then  lateral  crushing  of  the  earth's  crust,  such 
as  undoubtedly  occurs  in  mountain-making,  would  squeeze  the  liquid 
upward  into  and  through  fissures  to  the  surface,  producing  the  quieter 
lava-eruptions ;  or  else,  coming  in  contact  in  its  upward  course  with 
subterranean  waters,  especially  abundant  in  the  fissured  and  cavernous 
structure  of  recent  lavas,  would  develop  steam  and  therefore  violent 
explosive  eruptions. 

Subordinate  Volcanic  Phenomena. 

These  are  hot  springs,  carbonated  springs,  solfataras,  fumaroles, 
mud-volcanoes,  and  geysers.  They  are  all  secondary  phenomena,  i.  e., 
formed  by  the  percolation  of  meteoric  water  through  hot  volcanic  ejec- 
tions. Or  perhaps  in  some  cases  the  heat  may  be  produced  by  slow 
rock-crushing  by  horizontal  pressure,  as  explained  above,  or  else  by 
local  chemical  action. 

General  Explanation. — Thick  masses  of  lava  outpoured  from  vol- 
canoes remain  hot  in  their  interior  for  an  incalculable  time.  Water 
percolating  through  these  acquires  their  heat,  and  comes  up  again  as 
hot  springs ;  or,  if  in  addition  it  contains  lime,  as  lime-depositing 
springs ;  or,  if  it  contains  carbonic  acid,  as  carbonated  springs ;  or,  if 
it  contains  sulphurous  acid  and  sulphureted  hydrogen,  as  solfataras. 
If  condensible  vapors  issue  in  abundance  so  as  to  make  an  appearance 
of  smoke,  they  are  called  fumaroles.  If  the  hot  water  brings  up  with 
it  mud  which  accumulates  about  the  vent,  then  it  is  a  mud-spring  or 
a  mud- volcano.  If  the  heat  is  very  great,  so  that  violent  eruption  of 
water  takes  place  periodically,  then  it  becomes  a  geyser.  We  have 
already  spoken  of  carbonated  lime-depositing  springs  (p.  77).  We 
shall  again,  under  the  head  of  the  theory  of  mineral  veins  (p.  245), 
speak  of  solfataras.  The  only  one  which  need  detain  us  now  is  geysers. 

Geysers. 

A  geyser  may  be  defined  as  a  periodically  eruptive  spring.  Gey- 
sers are  found  only  in  Iceland,  in  the  Yellowstone  Park  of  the  United 
States,  and  in  New  Zealand.  The  so-called  geysers  of  California  are 
rather  fumaroles.  Those  of  Iceland  have  been  long  studied ;  we  will, 
therefore,  describe  these  first. 

Iceland  is  a  volcanic  plateau,  with  a  narrow  marginal  habitable 
region  sloping  gently  to  the  sea.  The  interior  plateau  is  the  seat  of 
every  species  of  volcanic  action,  viz.,  lava-eruptions,  solfataras,  mud- 
volcanoes,  hot  springs,  and  geysers.  There  are  several  hundred  vents 
of  all  .kinds  in  comparatively  small  space,  among  which  are  many  gey- 
sers. One  of  these,  the  Great  Geyser,  has  long  attracted  attention. . 

Description. — The  Great  Geyser  is  a  basin  or  pool  fifty-six  feet  in 


102 


IGNEOUS  AGENCIES. 


diameter,  on  the  top  of  a  mound  thirty  feet  high.  From  the  bottom  of 
the  basin  descends  a  funnel-shaped  pipe  eight  or  ten  feet  in  diameter, 
and  seventy-eight  feet  deep.  Both  the  basin  and  the  tube  are  lined 
with  silica,  evidently  deposited  from  the  water.  The  natural  inference 


is,  that  the  mound  is  built  up  by  deposit  from  the  water,  in  somewhat 
the  same  manner  as  a  volcanic  cone  is  built  up  by  its  own  ejections. 
In  the  intervals  between  the  eruptions  the  basin  is  filled  to  the  brim 


GEYSERS. 


103 


with  perfectly  transparent  water,  having  a  temperature  of  about  170° 
to  180°. 

Phenomena  of  an  Eruption. — 1.  Immediately  preceding  the  erup- 
tions sounds  like  cannonading  are  heard  beneath,  and  bubbles  rise  and 
break  on  the  surface  of  the  water.  2.  A  bulging  of  the  surface  is  then 
.seen,  and  the  water  overflows  the  basin.  3.  Immediately  thereafter 
the  whole  of  the  water  in 
the  tube  and  basin  is  shot 
upward  one  hundred  feet 
high,  forming  a  fountain 
of  dazzling  splendor.  4. 
The  eruption  of  water  is 
immediately  followed  by 
the  escape  of  steam  with  a 
roaring  noise.  These  last 
two  phenomena  are  repeat- 
ed several  times,  so  that 
the  fountain  continues  to 
play  for  several  minutes, 

until     the    Water    is     Suffi-  no.  86.-(After  Hayden.) 

ciently   cooled,   and    then 

all  is  again  quiet  until  another  eruption.  The  level  of  the  water  after 
an  eruption  is  seven  or  eight  feet  in  the  tube.  The  frequency  of  the 
eruptions  is  slowly  diminishing.  In  1804  it  was  once  every  hour ;  now 


FIG.  87.— The  Turban  (after  Hayden). 


several  days  often  elapse.*     Throwing  large  stones  into  the  tube  has 
the  effect  of  bringing  on  the  eruption  more  quickly. 

Yellowstone  Geysers. — In  magnificence  of  geyser  displays,  however, 
Iceland  is  far  surpassed  by  the  geyser  basin  of  Firehole  River. 


This 


*  Daubrcc,  Archives  des  Sciences,  vol.  xix,  p.  425,  1888. 


104 


IGNEOUS  AGENCIES. 


wonderful  geyser  region  is  situated  in  the  northwest  corner  of  Wyo- 
ming, on  an  elevated  volcanic  plateau  near  the  head-waters  of  the 
Madison  River,  a  tributary  of  the  Missouri,  and  of  the  Snake  River,  a 


FIG.  88.— Giant  Geyser  (after  Hayden). 


tributary  of  the  Columbia.  The  basin  is  only  about  three  miles  wide. 
About  it  are  abundant  evidences  of  prodigious  volcanic  activity  in  for- 
mer times,  and  although  primary  volcanic  activity  has  ceased,  second- 
ary volcanic  phenomena  are  developed  on  a  stupendous  scale  and  of 


GEYSERS. 


105 


every  kind,  viz. :  hot  springs,  carbonated  springs,  fumaroles,  mud-vol- 
canoes, and  geysers.  In  the  Yellowstone  Park  itself  there  are  at  least 
3,000  vents  of  all  kinds,  and  of  these  more  than  sixty  are  eruptive  gey- 
sers. In  some  places,  as  on  Gardiner's  River,  the  hot  springs  are  most- 
ly lime-depositing  (page  77) ;  in  others,  as  on  Firehole  River,  they  are 
geysers  depositing  silica. 


FIG.  89 — Bee-Hive  Geyser  (from  a  Drawing  by  Holmes). 

In  the  upper  geyser  basin  the  valley  is  covered  with  a  snowy  de- 
posit from  the  hot  geyser- waters.  The  surface  of  the  mound-like, 
chimney-like,  and  hive-like  elevations  (Fig.  90),  immediately  surround- 
ing the  vents,  is,  in  some  cases,  ornamented  in  the  most  exquisite 


106 


IGNEOUS   AGENCIES. 


manner  by  deposits  of  the  same,  in  the  form  of  scalloped  embroidery 
set  with  pearly  tubercles;  in  others  the  siliceous  deposits  take  the 
most  fantastic  forms  (Figs.  85,  86,  87).  In  some  places  the  silica  is 
deposited  in  large  quantities,  three  or  four  inches  deep,  in  a  gelatinous 

condition  like  starch-paste.  Trunks  and 
branches  of  trees  immersed  in  these 
waters  are  speedily  petrified. 

We  can  only  mention  a  few  of  the 
grandest  of  these  geysers  : 

1.  The  "  Grand  Geyser,"  according  to 
Hayden,  throws  up  a  column  of  water  six 
feet  in  diameter  to  the  height  of  200 
feet,  while  the  steam  ascends  1,000  feet 
or  more.     The  eruption  is  repeated  every 
thirty-two  hours,  and  lasts  twenty  min- 
utes.     In  a  state  of  quiescence  the  tem- 
perature of  the  water  at  the  surface  is 
about  150°. 

2.  The  "  Giantess"  throws  up  a  large 
column   twenty   feet   in   diameter   to   a 
height  of  sixty  feet,  and   through   this 
great  mass  it  shoots  up  five  or  six  lesser 
jets  to  a  height  of  250  feet.      Its  erup- 
tions are  fitful  but  last  sometimes  several 
hours. 

3.  The  "Giant"  (Fig.  88)  throws  a 
column  five  feet   in   diameter   140   feet 
high,  and   plays  continuously  for  three 
hours. 

4.  The   "Bee -Hive"   (Fig.  89),  so 
Hayden).                      called  from  the  shape  of  its  mound,  shoots 

up  a  splendid  column  two  or  three  feet  in  diameter  to  the  height  by 
measurement  of  219  feet,  and  plays  fifteen  minutes. 

5.  "  Old  Faithful,"  so  called  from  the  frequency  and  regularity  of 
its  eruptions,  throws  up  a  column  six  feet  in  diameter  to  the  height  of 
100  to  150  feet  regularly  every  hour,  and  plays  each  time  fifteen  minutes. 

Theories  of  Geyser-Eruption. — The  water  of  geysers  is  not  volcanic 
water,  but  simple  spring- water.  .  A  geyser  is  not,  therefore,  a  volcano 
ejecting  water,  but  a  true  spring.  There  has  been  much  speculation 
concerning  the  cause  of  their  truly  wonderful  eruptions. 

Mackenzie's  Theory. — According  to  Mackenzie,  the  eruptions  of  the 
Great  Geyser  may  be  accounted  for  by  supposing  its  pipe  connected 
by  a  narrow  conduit  with  the  lower  part  of  a  subterranean  cave, 
whose  walls  are  heated  by  the  near  vicinity  of  volcanic  fires.  Fig. 


FIG.  90.— Forms  of  Geyser-Craters  (after 


GEYSERS. 


10T 


91  represents  a  section  through  the  basin,  tube,  and  supposed  cave. 
Now,  if  meteoric  water  should  run  into  the  cave  through  fissures  more 
rapidly  than  it  can  evaporate,  it -would  accumulate  until  it  rose  above, 
and  therefore  closed,  the  opening  at  a.  The  steam,  now  having  no  out- 
let, would  condense  in  the  chamber  b  until  its  pressure  raised  the  water 
into  the  pipe,  and  caused  it  to  overflow  the  basin.  The  pressure  still 
continuing,  all  the  water 
would  be  driven  out  of 
the  cave,  and  partly  up 
the  pipe.  Now,  the  press- 
ure which  sustained  the 
whole  column  a  d  would 
not  only  sustain,  but 
eject  with  violence,  the 
column  c  d.  The  steam 
would  escape,  the  ejected 
water  would  cool,  and 

a     period    of     quiescence  ~  FIO.  91.-Mackenzie<8  Theory  of  Eruption. 

would  follow.      If  there 

were  but  one  geyser  in  Iceland,  this  would  be  rightly  considered  a  very 
ingenious  and  probable  hypothesis,  for  without  doubt  we  may  conceive 
of  a  cave  and  conduit  so  constructed  as  to  account  for  the  phenomena. 
But  there  are  many  eruptive  springs  in  Iceland,  and  it  is  inconceivable 
that  all  of  them  should  have  caves  and  conduits  so  peculiarly  con- 
structed. This  theory  is  therefore  entirely  untenable. 

Bunsen's  Investigations.  —  The  investigations  of  Bunsen  and  his 
theory  of  the  eruption  and  the  formation  of  geysers  are  among  the 
most  beautiful  illustrations  of  scientific  induction  which  we  have  in 
geology.  We  therefore  give  it,  perhaps,  more  fully  than  its  strict 
geological  importance  warrants. 

Bunsen  examined  all  the  phenomena  of  hot  springs  in  Iceland.  1. 
He  ascertained  that  geyser- water  is  meteoric  water,  containing  the 
soluble  matters  of  the  igneous  rocks  in  the  vicinity.  He  formed  iden- 
tical water  by  digesting  Iceland  rocks  in  hot  rain-water.  2.  He  ascer- 
tained that  there  are  two  kinds  of  hot  springs  in  Iceland,  viz.,  acid 
Brings  and  alkaline-carbonate  springs,  and  that  only  alkaline-car- 
bonate springs  contain  any  silica  in  solution.  The  reason  is  obvious; 
alkaline  waters,  especially  if  hot,  are  the  natural  solvents  of  silica.  3. 
He  ascertained  that  only  the  silicated  springs  form  geysers.  Here  is 
one  important  step  taken — one  condition  of  geyser-formation  discov- 
ered. Deposit  of  silica  is  necessary  to  the  existence  of  geysers.  The 
tube  of  a  geyser  is  not  an  accidental  conduit,  but  is  built  up  by  its  own 
deposit.  4.  Of  silicated  springs,  only  those  with  deep  tubes  erupt — 
another  condition.  5.  Contrary  to  previous  opinion,  the  silica  in  solu- 


108 


IGNEOUS  AGENCIES. 


Pressure  in 
Atmospheres. 

Boiling-Point. 

1  Atmos. 

212° 

2 

250° 

3         " 

275° 

4 

293° 

tion  does  not  deposit  on  cooling,  but  only  by  drying.  This  would  make 
the  building-up  of  a  geyser- tube  an  inconceivably  slow  process,  and  the 
time  proportionally  long.  6.  The  temperature  of  the  water  in  the  basin 
was  found  to  be  usually  170°  to  180°,  and  that  in  the  tube  to  increase 
rapidly,  though  not  regularly,  with  depth.  Moreover,  the  temperature, 
both  at  the  surface  and  at  all  depths,  increased  regularly  as  the  time  of 
eruption  approached.  Just  before  the  eruption  it  was,  at  the  depth  of 
about  forty-five  feet,  very  near  the  boiling-point  for  that  depth. 

Theory  of  Geyser-Eruption—Principles. — 1.  It  is  well  known  that 
the  boiling-point  of  water  rises  as  the  pressure  increases.  This  is  shown 
in  the  adjoining  table.  2.  It  follows  from  the 
above  that  if  water  be  under  strong  pressure, 
and  at  high  temperature,  though  below  its 
boiling-point  for  that  pressure,  and  the  press- 
ure be  diminished  sufficiently,  it  will  immedi- 
ately flash  into  steam.  3.  Water  heated  be- 
neath, if  the  circulation  be  unimpeded,  is  very 
nearly  the  same  temperature,  throughout.  That  it  is  never  the  same 
temperature  precisely  is  shown  by  the  circulation  itself,  which  is  caused 
by  difference  of  temperature,  producing  difference  in  density.  The 
phenomenon  of  simmering  is  also  a  well-known  evidence  of  this  differ- 
ence of  temperature,  since  it  is  produced  by  the  collapse  of  steam-bub- 
bles rising  into  the  cooler  water  above.  4.  But  if  the  circulation  be 
impeded,  as  when  the  water  is  contained  in  long,  narrow,  irregular 
tubes,  and  heated  with  great  rapidity,  the  temperature  may  be  greater 
below  than  above  to  any  extent,  and 
the  boiling-point  may  be  reached  in 
the  lower  part  of  the  tube,  while  it  is 
far  from  this  point  in  the  upper  part. 
Application  to  Geysers. — We  will 
suppose  a  geyser  to  have  a  simple  but 
irregular  tube,  without  a  cave,  heated 
below  by  volcanic  fires,  or  by  still  hot 
volcanic  ejections.  Now,  we  have  al- 
ready seen  that  the  temperature  of  the 
water  in  the  tube  increases  rapidly  with 
the  depth,  but  is,  at  every  depth  to 
which  observation  extends,  short  of  the 
boiling-point  for  that  depth.  Let 
absciss  a  d  (Fig.  92)  represent  depth 
in  the  tube,  and  also  pressures ;  and  the  corresponding  temperature  be 
measured  on  the  ordinate  a  n.  If,  then,  ab,bc,cd,  represent  equal 
depths  of  thirty-three  or  more  feet,  which  is  equal  to  one  atmospheric 
pressure,  the  curve  ef  passing  through  212°,  250°,  275°,  and  293°,  at  the 


1  Atmos. 


3  Atmos. 
33-3  ft. 


3  Atmos. 
66-6  ft. 


4  Atmos. 
100ft. 


n 


a 


FIG.  92. 


GEYSERS. 


109 


horizontal  lines,  representing  one  atmosphere,  two  atmospheres,  three 
atmospheres,  etc..,  would  correctly  represent  the  increasing  boiling- 
points  as  we  pass  downward.  We  shall  call  this  liile,  ef,  the  curve  of 
boiling-point.  The  line  a  g  commencing  at  the  surface  at  180°,  and 
gradually  approaching  the  boiling-point  line,  but  everywhere  within  it, 
would  represent  the  actual  temperature  in  a  state  of  quiescence.  We 
shall  call  this  the  line  of  actual  temperature.  Now,  Bunsen  found  that, 
as  the  time  of  eruption  approached,  the  temperature  at  every  depth 
approached  the  boiling-point  for  that  depth — i.  e.,  the  line  a  g  moved 
toward  the  line  ef.  There  is  no  doubt,  therefore,  that,  at  the  moment 
of  eruption,  at  some  point  below  the  reach  of  observation,  the  line  a  g 
actually  touches  the  line  ef — the  boiling-point  for  that  depth  is  actually 
reached.  As  soon  as  this  occurs,  a  quantity  of  water  in  the  lower  por- 
tion of  the  tube,  or  perhaps  even  in  the  subterranean  channels  which 
lead  to  the  tube,  would  be  changed  into  steam,  and  the  expanding  steam 
would  lift  the  whole  column  of  water  in  the  tube,  and  cause  the  water 
in  the  basin  to  bulge  and  overflow.  As  soon  as  the  water  overflowed, 
the  pressure  would  be  diminished  in  every  part  of  the  tube,  and  conse- 
quently a  large  quantity  of  water  before  very  near  the  boiling-point 
would  flash  into  steam  and  instantly  eject  the  whole  of  the  water  in 
the  pipe ;  and  the  steam  itself  would  rush  out  immediately  afterward. 
The  premonitory  cannonading  beneath  is  evidently  produced  by  the 
collapse  of  large  steam-bubbles  rising  through  the  cooler  water  of  the 
upper  part  of  the  tube;  in  other  words,  it  is  simmering  on  a  huge  scale. 
An  eruption  is  more  quickly  brought  on  by  throwing  stones  into  the 
throat  of  the  geyser,  because  the 

circulation  is  thus  more  effectu- *       a 

ally  impeded. 

The  theory  given  above  is  sub- 
stantially that  of  Bunsen  for  the 
eruption  of  the  Great  Geyser,  but 
modified  to  make  it  applicable  to 
all  geysers.  In  the  Great  Geyser, 
as  already  stated,  Bunsen  found  a 
point  forty-five  feet  deep,  where 
the  temperature  was  nearer  the 
boiling-point  than  at  any  within 
reach  of  observation.  This  point, 

forty-five  feet  deep,  .plays  an  im-  FlG  93 

portant  part  in  Bunsen's  theory. 

To  illustrate  :  if  ef  (Fig.  9,3)  represent  again  the  curve  of  boiling-point, 
then  the  curve  of  actual  temperature  in  the  Great  Geyser  tube  would 
be  the  irregular  line  a  g  h.  At  the  moment  of  eruption,  this  line 
touched  boiling-point  at  g.  Then  would  follow  the  instantaneous  for- 


c66ft 
d  100 ft 


110 


IGNEOUS  AGENCIES. 


mation  of  steam,  and  itlie  phenomena  of  an  eruption.     But  it  is  ex- 
tremely unlikely  that  this  condition  should  exist  in  all  geysers ;  neither 
is  it  at  all  necessary  in  order  to  explain  the  phenomenon  of  an  eruption. 
To  prove  beyond  question  the  truth  of  this  theory,  Bunsen  con- 
structed an  artificial  geyser.     The  apparatus  (Fig.  94)  consisted  of  a 
tube  of  tinned  sheet-iron  about  ten  feet  long,  expanded  into  a  dish 
above  for  catching  the  erupted  water.    It  may  or  may  not  be  expanded 
^  below  for  the  convenience  of  heating.     It  was  heated, 

J|j^  ,  also,  a  little  below  the  middle,  by  an  encircling  char- 

coal chauffer,  to  represent  the  point  of  nearest  ap- 
proach to  the  boiling-point  in  the  geyser -tube. 
AY  hen  this  apparatus  was  heated  at  the  two  points, 
as  shown  in  the  figure,  the  phenomena  of  geyser- 
eruption  were  completely  reproduced :  first,  the  vio- 
lent explosive  simmering,  then  the  overflow,  then  the 
eruption,  and  then  the  state  of  quiescence.  In  Bun- 
sen's  experiment,  the  eruptions  occurred  about  every 
thirty  minutes. 

Bunsen's  Theory  of  Geyser-Formation. — Accord- 
ing to  Bunsen,  a  geyser  does  not  find  a  cave,  or  even 
a  perpendicular  tube,  ready  made,  but,  like  volcanoes, 
makes  its  own  tube.  Fig.  95  is  an  ideal  section  of  a 
geyser-mound,  showing  the  manner  in  which,  accord- 
ing to  this  view,  it  is  formed.  The  irregular  line, 
b  a  c,  is  the  original  surface,  and  a  the  position  of  a 
hot  spring.  If  the  spring  be  not  alkaline,  it  will 
remain  an  ordinary  hot  spring ;  but,  if  it  be  alka- 
line, it  will  hold  silica  in  solution,  and  the  silica  will 
he  deposited  about  the  spring.  (  Thus  the  mound 
and  tube  are  gradually  built  up.  For  a  long  time  the 
spring  will  not  be  eruptive,  for  the  circulation  will 
maintain  a  nearly  equal  temperature  in  every  part 
of  the  tube — it  may  be  a  boiling,  but  not  an  eruptive 
spring.  But,  as  the  tube  becomes  longer,  and  the  circulation  more  and 
more  impeded,  the  difference  of  temperature  between  the  upper  and 
lower  parts  of  the  tube  becomes  greater  and  greater,  until,  finally,  the 
boiling-point  is  reached  below,  while  the  water  above  is  comparatively 
cooly  Then  the  eruption  commences.  Finally,  from  the  gradual  fail- 
ure of  the  subterranean  heat,  or  from  the  increasing  length  of  the  tube 
repressing  the  formation  of  steam,  the  eruptions  gradually  cease.  Bun- 
sen  found  geysers  in  different  stages  of  development — some  playful 
springs  without  tubes ;  some  with  short  tubes,  not  yet  eruptive  ;  some 
with  long  tubes,  violently  eruptive ;  some  becoming  old  and  indisposed 
to  erupt  unless  angered  by  throwing  stones  down  the  throat. 


FIG. 


94.— Artificial 
Geyser. 


EARTHQUAKES. 


Ill 


It  is  evident,  however,  that  Bunsen's  theory  of  geyser-eruption  is. 
independent  of  his  theory  of  geyser-formation.     A  tube  or  fissure  of 
any  kind,  and  formed  in  any 
way,   if   long   enough,  would 
give    rise   to   the    same   phe- 
nomena.      The    Yellowstone 
geysers  have  mounds  or  chim- 
ney-like  cones,  but   it   is   by 
no    means    certain    that    the 
whole  length  of  their  eruptive 
tubes  has   been  built  up  by 
siliceous  deposit.  Bunsen's  the- 
ory of  eruption  none  the  less,   - 
however,  applies  to  these  also.  "tion  g^™'™*' according  to 

SECTION  3. — EARTHQUAKES. 

Only  very  recently,  and  mainly  through  the  labors  of  Mr.  Mallet,*  of 
England,  our  knowledge  on  the  subject  of  earthquakes  has  commenced 
to  take  on  scientific  form.  This  slowness  of  advance  has  arisen  not 
from  any  want  of  materials,  but  from  the  great  complexity  of  the  phe- 
nomena, their  origin  deep  within  the  bowels  of  the  earth  and  there- 
fore removed  from  observation,  and,  more  than  all,  from  the  surprise; 
and  alarm  usually  produced  unfitting  the  mind  for  scientific  observa- 
tion. For  these  reasons,  until  twenty  or  thirty  years  ago,  the  state  of 
knowledge  on  this  subject  was  much  the  same  as  it  was  2,000  years  ago. 
And  yet  now,  we  think,  our  knowledge  of  earthquakes  is  even  more 
advanced  than  that  of  volcanoes. 

Frequency. — Mallet,  in  his  earthquake  catalogue,  has  collected  the 
records  of  6,830  earthquakes  as  occurring  in  3,456  years  previous  to 
1850;  but,  of  that  number,  3,240,  or  nearly  one  half,  occurred  in  the 
last  fifty  years ;  not  because  earthquakes  were  more  numerous,  but  be- 
cause the  records  were  more  perfect.  According  to  the  more  complete 
catalogue  of  Alexis  Perrey,f  from  1843  to  1872,  inclusive,  there  were 
17,249,  or  575  per  annum.  In  Japan  alone  there  are,  on  an  average,  two 
shocks  per  day.J  It  seems  probable,  therefore,  that,  considering  the 
fact  that  even  now  the  larger  number  of  earthquakes  are  not  recorded, 
occurring  in  mid-ocean  or  in  uncivilized  regions,  the  earth  is  constantly 
quaking  in  some  portion  of  its.  surface. 

Connection  with  other  Forms  of  Igneous  Agency. — The  close  connec- 
tion of  earthquakes  with  volcanoes  is  undoubted  :  1.  Volcanic  eruptions, 

*  Transactions  of  British  Association,  1850-1858  ;  also,  Principles  of  Seismology. 
f  American  Journal  of  Science,  vol.  xi,  p.  233,  1876. 

|  Transactions  of  the  Scismological  Society  of  Japan,  vol.  vi,  Part  II,  p.  79.  Nature, 
vol.  xl,  p.  657,  1 889. 


112  IGNEOUS  AGENCIES. 

especially  those  of  the  explosive  type,  are  always  preceded  and  accom- 
panied by  earthquakes.  2.  Earthquake-shocks  which  have  continued  to 
trouble  a  particular  region  for  a  long  time,  often  suddenly  cease  when 
an  outburst  takes  place  in  a  neighboring  volcano,  showing  that  the 
latter  are  safety- vents  for  the  interior  forces  which  produce  earthquakes. 
Also,  the  sudden  cessation  of  accustomed  volcanic  activity  will  often 
bring  on  earthquakes.  Thus,  when  the  wreath  of  smoke  disappears 
from  Cotopaxi,  the  inhabitants  of  Q.uito  expect  earthquakes.  During 
the  great  Calabrian  earthquakes  of  1783,  Stromboli,  for  the  first  time  in 
the  memory  of  man,  ceased  erupting.  The  great  earthquake  which  de- 
stroyed Riobamba  in  1797,  and  in  which  40,000  persons  perished,  took 
place  immediately  after  the  stopping  of  activity  in  a  neighboring  vol- 
cano. The  earthquake-shocks  which  destroyed  Caracas  in  1812  ceased 
as  soon  as  St.  Vincent,  500  miles  distant,  commenced  erupting.  3.  Ex- 
amination of  Prof.  Mallet's  earthquake-map  shows  that  the  distribution 
of  earthquake-centers  is  much  the  same  as  that  of  volcanoes  already 
given  (page  88).  It  may  be  regarded  as  almost  certain,  therefore,  that 
the  forces  which  generate  earthquakes  are  closely  allied,  if  not  identical, 
with  those  which  produce  volcanic  eruptions.  ,v 

Again,  the  connection  of  earthquakes  with  bodily  movements  of 
great  areas  of  the  earth's  crust,  by  elevation  or  depression,  is  equally 
close.  In  1835,  after  a  great  earthquake,  which  shook  the  coast  of 
South  America  over  an  area  of  600,000  square  miles,  the  whole  coast- 
line of  Chili  and  Patagonia  was  found  elevated  from  two  to  ten  feet 
above  sea-level.  Again,  in  1822,  after  a  similar  earthquake  in  the  same 
region,  the  coast-line  was  found  elevated  from  two  to  seven  feet.  Now, 
in  this  very  region,  old  beach-marks,  100  feet  to  1,300  feet  above  the 
sea-level,  and  extending  1,200  miles  along  the  coast  on  each  side  of  the 
southern  end  of  this  continent,  plainly  show  that,  in  very  recent  geo- 
logical times,  the  whole  southern  end  of  South  America  has  been  bodily 
raised  out  of  the  sea  to  that  extent.  It  is  impossible  to  doubt  that  the 
force  which  produced  this  continental  elevation  was  also  the  cause  of 
the  accompanying  earthquakes.  Again,  in  1819,  after  a  severe  earth- 
quake, which  shook  the  whole  region  about  the  mouth  of  the  Indus,  a 
large  tract  of  land  of  2,000  square  miles  was  sunk  and  became  a  salt 
lagoon ;  while  another  area,  fifty  miles  long  and  ten  to  sixteen  miles 
wide,  was  elevated  ten  feet.  In  commemoration  of  this  wonderful 
event,  the  raised  portion  was  called  Ullah  Bund,  or  the  Mound  of  God. 
Again,  in  1811,  a  severe  earthquake  shook  the  valley  of  the  Missis- 
sippi. In  the  region  about  the  mouth  of  the  Ohio,  where  it  was  se- 
verest, large  tracts  of  land  were  sunk  bodily  several  feet  below  their  for- 
mer level,  and  have  been  covered  with  water  ever  since.  It  is  now 
called  the  "  Sunk  Country"  The  Inyo  earthquake  of  1872  was  ac- 
companied by  a  fissure  of  forty  miles  in  length  and  a  slip  or  fault  of 


EARTHQUAKES.  113 

twenty-five  feet.*  In  the  Sonora  earthquake  of  1887  there  was  a  fissure 
for  a  hundred  miles  and  a  vertical  slip  of  eight  feet.f  We  might 
multiply  examples  if  necessary.  Nearly  all  earthquakes,  if  carefully 
studied,  have  shown  such  fissures  and  slips.  Fissures  and  faults, 
formed  in  previous  geological  times,  are  found  intersecting  the  earth 
in  all  directions.  We  see  them,  in  these  cases,  formed  under  our 
eyes,  and  in  connection  with  earthquakes. 

Ultimate  Cause  of  Earthquakes. — The  connection  of  earthquakes 
with  the  two  other  forms  of  igneous  agency  suggests  each  a  possible 
cause.  Preceding  and  accompanying  volcanic  eruptions,  especially  of 
the  explosive  type,  occur  subterranean  explosions,  which  are  often  heard 
hundreds  of  miles.  Such  eruptions  are  also  accompanied  with  escape  of 
immense  quantities  of  steam  and  gas.  These  facts,  together  with  the 
association  of  earthquakes  with  volcanoes,  have  suggested  the  idea  that 
the  sudden  formation  or  the  sudden  collapse  of  vapor  is  the  cause  of 
earthquakes.  According  to  this  view,  an  earthquake  is,  on  a  grand 
scale,  a  phenomenon  similar  to  the  jar  produced  by  the  explosion  of  a 
keg  of  gunpowder  buried  in  the  earth. 

But  the  association  of  earthquakes  with  bodily  movements  of  the 
earth's  crust  over  large  areas,  suggests  another  and  far  more  probable 
cause.  It  is  well  known  that  there  are  operating,  in  the  interior  of  the 
earth,  forces  tending  to  elevate  or  depress  or  to  crush  together  laterally 
the  earth's  crust.  We  shall  discuss  the  nature  of  these  forces  here- 
after. Suffice  it  to  say  now  that  in  this  way  mountain-ranges  are 
formed  and  continents  elevated.  One  effect  of  these  forces  is  to  break 
the  earth's  crust  into  great  blocks  many  miles  in  length  and  breadth 
and  several  miles  in  thickness.  These  blocks  do  not  remain  in  their 
original  position,  but  are  always  slipped  one  on  another,  producing  dis- 
placement often  thousands  of  feet.  Such  great  crust-blocks  separated 
by  profound  fissures,  and  slipped  one  on  another,  are  found  everywhere. 
They  are,  in  fact,  among  the  commonest  of  geological  occurrences. 
They  will  be  described  in  Part  II.  Some  of  these  fissures  are  doubt- 
less now  forming ;  many  of  them  are  still  slipping.  Suppose,  then, 
a  subterranean  force,  tending  to  elevate  a  portion  of  the  earth's  crust, 
and  gradually  increasing  but  resisted  by  the  rigidity  of  the  crust.  It 
is  evident  that  the  time  would  finally  come  when  the  crust  would  break, 
by  a  fracture  extending  perhaps  hundreds  of  miles  in  length  and 
through  several  miles  in  depth  of  solid  rock.  Such  a  fracture  would  cer- 
tainly cause  an  earth -jar  great  enough  to  produce  all  the  dreadful 
effects  of  an  earthquake.  But,  again,  the  enormous  crust-blocks  thus 
formed  would  inevitably  from  time  to  time  settle,  or  readjust  them- 
selves to  new  positions.  Every  such  readjustment  would  also  produce 

*  Gilbert,  Nat.,  vol.  xxix,  p.  45,  1883.  f  Science,  vol.  x,  p.  81,  1887. 

8 


114 


IGNEOUS  AGENCIES. 


an  earthquake.  We  conclude,  therefore,  that  ly  far  the  most  common 
cause  of  earthquakes  is  either  the  formation  of  a  great  fissure  or  else 
the  readjustment  of  the  walls  of  such  a  fissure.  Even  in  the  case  of 
the  tremors  accompanying  volcanic  eruptions,  it  is  probable  that  their 
true  cause  is  the  fracturing  of  the  mountain  by  the  eruptive  forces  and 
the  readjusment  of  the  broken  parts. 

Proximate  Cause. — But  whatever  be  our  view  of  the  ultimate  cause 
of  earthquakes,  there  can  be  no  doubt  that  the  proximate  or  immediate 
cause  of  the  observed  effects  is  the  arrival  of  an  earth-jar — the  emer- 
gence, on  the  earth- surf  ace,  of  a  succession  of  elastic  earth- waves,  pro- 
duced by  a  violent  concussion  of  some  kind  in  the  interior.  Evidently, 
therefore,  the  discussion  of  earthquake-phenomena  is  nothing  more 
than  the  discussion  of  the  laws  of  propagation  and  the  effects  of  elastic 
earth- waves  occurring  under  peculiar  and  very  complex  conditions. 

Application  to  Earthquakes, — Suppose,  then,  a  concussion  of  any 
kind  to  occur  at  a  considerable  depth  (x,  Fig.  96),  say  ten  or  twenty  miles, 
beneath  the  earth-surface,  S  S.  Taking,  for  simplicity  sake,  the  origin 
as  a  point,  a  series  of  elastic  spherical  waves,  similar  to  sound-waves, 
will  be  generated,  consisting  of  alternate  compressed  and  rarefied  shells, 
the  whole  expanding  with  great  rapidity  in  all  directions  until  they 
reach  the  surface  at  a.  From  this  point  of  first  emergence  immediately 
above  the  focus  #,  the  still- enlarging  spherical  shells  would,  outcrop  in 
rapidly-expanding  circular  waves,  V  b",  c"  c,"  d"  d"  (Fig.  96),  similar 


FIG.  96.— Section  and  Perspective  View  of  a  Portion  of  the  Earth's  Crust  shaken  by  an  Earthquake, 
showing  the  origin,  x,  sections  of  the  spherical  waves,  a,  b,  c}  d,  etc.,  and  perspective  of  surface- 
wave,  b",  c",  d",  etc. 

in  form  to  water-waves,  but  very  different  in  character.  This  we  will 
call  the  surface-wave.  The  circles  here  drawn  would  equally  represent  a 
series  of  waves,  or  the  same  wave  in  successive  degrees  of  enlargement. 
This  surface-wave  would  not  be  a  normal  wave  propagating  itself 
like  a  water-wave.  It  would  be  only  the  outcropping  or  emergence  of 
the  ever- widening  spherical  wave  on  the  earth-surface.  Both  its  velocity 
of  transit  along  the  surface,  and  the  direction  of  its  vibration  in  relation 
to  the  surface,  will  vary  continually  according  to  a  simple  law.  The 
direction  of  vibration,  being  along  the  radii  x  a,  x  b,  x  c,  etc.,  will  be 


EARTHQUAKES. 


115 


perpendicular  to  the  surface  at  «,  and  become  more  inclined  until  it 
finally  becomes  parallel  with  the  surface  at  an  infinite  distance.  The 
velocity  of  its  transit  will  be  infinite  at  0,  and  then  gradually  decrease 
until,  if  we  regard  the  surface  as  a  plane  surface,  at  an  infinite  distance 
it  reaches  its  limit,  which  is  the  velocity  of  the  spherical  wave.  Between 
these  two  extremes  of  infinity  at  «,  and  the  velocity  of  the  spherical 
wave  at  infinite  distance,  the  velocity  of  the  surf  ace- wave  varies  in- 
versely as  the  cosine,  or  directly  as  the  secant,  of  the  angle  of  emergenco 
xba,xca,  etc. 

For,  if  a  a,  b  b,  c  c,  d  d,  etc.  (Fig.  9G),  be  successive  positions  of  the 
spherical  wave,  then  the  radii  x  a,  x  b,  x  c,  would  be  the  direction  both 
of  propagation  and  of  vibration.  Now,  when  the  wave-front  is  at  #, 
while  the  spherical  wave  moves  from  V  to  c,  the  surf  ace- wave  would 
move  from  b  to  c ;  when  the  spherical  wave  moves  from  c'  to  d,  the  sur- 
face-wave moves  from  c  to  rf,  etc.  If,  therefore,  b  c,  c  d,  etc.,  be  taken 
very  small,  so  that  b  V  c,  c  c'  d,  may  be  considered  right-angled  tri- 
angles, then  in  every  position  the  surface- wave  moves  along  the  hypote- 
nuse, while  the  spherical  wave  moves  along  the  base  of  the  small  tri- 
angles b  V  c,  c  c'  d,  etc.  Letting  v  =  velocity  of  the  spherical  wave,  and 
v'  that  of  the  surface-wave,  and  E  the  angle  of  emergence  (x  ba,  x  ca, 
etc.,  Fig.  96),  we  have  the  proportion — v  :  v'  : :  1 :  sec.  E,  and  v'=  v.  sec. 
E,  or  if  v  is  constant  v'  a  sec.  E.  Therefore,  at  a,  the  point  of  first 
emergence,  E  being  a  right  angle  and  sec.  E  =  infinity,  v'  =  infinity. 
At  an  infinite  distance  from  a  the  angle  E  becomes  0,  and  the  secant 


FIG.  97. 

=  1,  and  v'=  v.  1  =  v.  That  is,  at  the  point  of  first  emergence  the  ve- 
locity of  the  surface- wave  is  infinite  ;  from  this  point  it  decreases  as  the 
secant  of  the  angle  of  emergence  decreases, 
until  finally  at  an  infinite  distance  it  becomes 
equal  to  the  velocity  of  the  spherical  wave. 

On  a  spherical  surface  (Fig.  97)  it  is  evi- 
dent that  E  never  becomes  0,  and  therefore 
v'  never  reaches  the  limit  v.  If  we  conceived 
the  wave  to  pass  through  the  whole  earth  (Fig. 
98),  then  the  velocity  of  the  surface-wave 
would  decrease  to  a  certain  point  where  E  is 
a  minimum,  say  about  c,  and  then  would  again 
increase  to  infinity  on  the  other  side  of  the 
earth,  p,  where  E  becomes  again  a  right  angle. 


If  x  be  near  the  sur- 


IGNEOUS  AGENCIES. 

face,  v'  would  become  nearly  equal  to  v  at  some  point  of  its  course ;  but 
as  x  approaches  the  center,  (7,  the  limit  of  v'  would  be  greater  and 
greater,  until,  if  x  is  at  the  center,  v'  would  become  infinite  everywhere ; 
i.  e.,  a  shock  at  the  center  would  reach  the  surface  everywhere  at  the 
same  moment. 

Experimental  Determination  of  the  Velocity  of  the  Spherical  Wave. 
— On  the  supposition  that  earthquakes  are  really  produced  by  the  emer- 
gence on  the  surface  of  a  series  of  elastic  earth- waves,  Mallet  under- 
took to  determine  experimentally  the  velocity  of  such  waves.  Two 
stations  were  taken  about  a  mile  or  more  apart,  and  connected  by  tele- 
graphic apparatus  ;  a  keg  of  gunpowder  was  buried  at  one,  and  at  the 
other  was  placed  an  observatory,  in  which  was  a  clock,  a  mercury  mir- 
ror, and  a  light,  the  image  of  which  reflected  from  the  mercury  mirror 
was  thrown  on  a  screen.  The  slightest  tremor  communicated  to  the 
mercury  surface  of  course  caused  the  image  to  dance.  The  moment 
of  explosion  was  telegraphed ;  the  moment  of  arrival  of  the  earth- 
tremor  was  observed.  The  difference  gave  the  time  of  transit ;  the 
distance,  divided  by  the  time,  gave  the  velocity  per  second.  In  this 
manner  Mallet  found  the  velocity  in  sand  825  feet  per  second,  or  nearly 
nine  and  one  half  miles  per  minute ;  in  slate  1,225  feet  per  second,  or 
fourteen  miles  per  minute ;  and  in  granite  1,665  feet  per  second,  or 
nineteen  miles  per  minute.  As  an  earthquake-focus  is  always  several 
miles  beneath  the  surface,  and  as  rocks  at  that  depth  are  probably  as 
hard  as  granite,  nineteen  miles  per  minute  may  be  taken  as  the  aver- 
age velocity  of  earth-waves  as  determined  by  these  experiments.  It 
agrees  well  with  the  observed  velocity  of  many  earthquakes.* 

This  result  was  unexpected,  considering  the  law  that  all  elastic 
waves  in  the  same  medium  run  with  the  same  velocity,  for  the  velocity 
of  sound  in  granite  or  slate  is  probably  not  less  than  10,000  or  12,000 
feet  per  second.  The  explanation  is  to  be  found  in  the  very  imperfect 
coherence  and  elasticity  of  rocks.  The  medium  is  broken  by  the  pas- 
sage of  large  and  high  waves  of  the  explosion,  but  carries  successfully 
the  small  waves  of  sound. 

More  recent  experiments  have  given  much  higher  velocities.  In  a 
series  of  very  careful  experiments  Fouque  f ound>  in  sand  a  velocity  of 
984  feet,  in  carboniferous  sandstone  about  7,400  feet,  and  in  granite 
about  9,200  feet  per  second. f  The  explosion  at  Hallett's  Point  gave 
5,000  to  8,000  feet  per  second,  and  that  of  Flood  Rock,  4,500  to  20,000 
feet  per  second  (Abbot).  These  agree  well  with  the  observed  velocity  of 
some  earthquakes. 

Character  of  the  Earth-Wave. — For  the  sake  of  simplicity  we  have 

*  Mallet,  Second  Report,  Transactions  of  the  British  Association,  1851. 
f  Revue  Scientifique,  vol.  xli,  pp.  97,  161,  1888. 


EARTHQUAKES.  H7 

4k 

thus  far  spoken  of  the  earth-wave  as  a  simple  spherical  wave  of  longi- 
tudinal vibration  like  a  sound-wave,  but  the  seismograph  shows  that 
there  are  transverse  as  well  as  longitudinal  vibrations.  Thus,  the  earth- 
movement  is  very  complex  and  produced  by  the  superposition  of  several  ' 
waves  of  different  kinds.  But  the  wave  which  we  have  been  discussing 
is  the  dominant  one  and  the  one  whose  origin  is  most  easily  understood, 


FIG.  99- Model  showing  the  Path  of  a  Particle  during  an  Earthquake  (after  Sekiya). 

and  is  therefore  called  the  normal  wave.  Fig.  99  is  a  wire  model  rep- 
resenting the  actual  motion  of  a  point  during  an  earthquake.  It  was 
made  by  combining  the  records  of  the  three  pendulums  of  Ewing's 
seismograph  (Fig.  lO^)- 

Explanation  of  Earthquake-Phenomena. — Earthquakes  have  been 
divided  into  three  kinds,  viz.,  the  explosive,  the  horizontally  progres- 
sive, and  the  vorticose.  The  first  kind  is  described  by  Humboldt  as 
a  violent  motion  directly  upward,  by  which  the  earth-crust  is  broken 
up,  and  bodies  on  the  surface  are  thrown  high  in  the  air.  The  shock 
is  extremely  violent,  but  does  not  extend  very  far.  In  the  second,  the 
shock  spreads  on  the  surface  like  the  waves  on  water  to  a  great  dis- 
tance. In  the  third  there  is  a  whirling  motion  of  the  earth  entirely 
different  from  ordinary  wave-motion.  These  three  kinds  are  sometimes 
supposed  to  be  essentially  distinct,  and  possibly  produced  by  different 
causes ;  but  we  will  attempt  to  show  that  the  difference  is  wholly  due 
to  the  different  conditions  under  which  the  waves  emerge  on  the  sur- 
face. The  three  kinds  are,  in  fact,  often  united  in  the  same  earth- 
quake. 

The  most  remarkable  example  of  explosive  earthquake  is  that  which 
destroyed  Riobamba  in  1797.  In  this  dreadful  earthquake  the  shock 
came  suddenly,  like  the  explosion  of  a  mine.  Not  only  was  the  earth 
broken  up  and  rent  in  various  places,  but  objects  lying  on  the  surface 
of  the  earth  were  thrown  violently  upward  ;  bodies  of  men  were  hurled 


118 


IGNEOUS  AGENCIES. 


several  hundred  feet  in  the  air,  and  afterward  were  found  across  a  river 
and  on  the  top  of  a  hill.  In  earthquakes  of  this  kind — 1.  The 
impulse  is  very  powerful  and  sudden,  so  as  to  make  a  high  but  not 
a  long  wave,  or,  in  other  words,  the  velocity  of  vibration  or  of  the 
shock  is  very  great;  and,  2.  The  focus  is  not  deep,  so  that  the 
velocity  of  the  shock-motion  does  not  become  small  before  it  reaches 
the  surface.  At  Eiobamba  the  velocity  of  the  shock-motion  was  still 
very  great  when  the  wave  reached  the  surface.  From  the  distance 
bodies  were  thrown,  Mallet  supposes  the  velocity  of  the  shock-motion 
could  not  have  been  less  than  eighty  feet  per  second  (Jukes). 

The  horizontally  progressive  kind  may  be  regarded  as  the  true 
type  of  an  earthquake ;  it  is  in  fact  the  spreading  surf  ace- wave  al- 
ready explained.  If  the  elasticity  of  the  earth,  and  therefore  the 
velocity  of  the  waves,  is  the  same  in  all  directions,  the  surface-wave 
will  spread  in  concentric  circles;  but  if  the  elasticity,  and  therefore 
the  velocity  of  the  waves,  be  greater  in  one  direction  than  in  another, 
as,  for  example,  north  and  south  than  east  and  west,  or  the  converse, 
then  the  form  of  the  outcrop  will  be  elliptical.  In  some  rare  cases  the 
shock  seems  to  run  along  a  line.  Thus  progressive  earthquakes  have 
been  subdivided  into  circular,  elliptical,  and  linear  progressive.  We 
have  already  given  the  simple  explanation  of  the  first  two;  the  last 
may  be  briefly  explained  as  follows : 

Let  it  be  borne  in  mind :  1.  That  these  linear  earthquakes  usually 
run  along  mountain- chains;  2.  That  most  great  mountain-chains  consist 
of  a  granite  axis  (appearing  along  the  crest  and  evidently  connected  be- 
neath with  the  great  interior  rocky  mass  of  the  earth),  flanked  on  each 
side  with  stratified  rocks  consisting  of  many  different  kinds ;  3.  When 
elastic  waves  pass  from  one  medium  to  another  of  different  elasticity, 
in  all  cases  a  part  of  the  wave  passes  through,  but  a  part  is  always 
reflected.  For  every  such  change — for  every  layer — a  reflection  occurs ; 
and,  therefore,  if  there  are  many  such  layers,  the  waves  are  quickly 
quenched.  If,  now,  Fig.  100  represent  a  transverse  section  across 


FIG.  100.— Diagram  illustrating  Linear  Earthquakes. 


such  a  mountain,  and  X  the  focus  of  an  earthquake,  it  is  evident  that 
the  portion  of  the  enlarging  spherical  wave  which  emerged  along  the 


EARTHQUAKES. 

axis  a  would  reach  the  surface  successfully ;  while  those  portions  which 
struck  against  the  strata  of  the  flanks  would  be  partially  or  wholly 
quenched.  The  mode  of  outcrop  on  the  surface  is  shown  in  the  map- 
view,  Fig.  101,  in  which  a  is  the  epicentrum,  b  b  the  granite  axis,  and 
c  c  the  stratified  flanks.  It  must  be  remembered  also  that  the  origin  of 
most  earthquakes  is  by  the  formation  or  the  readjustment  of  a  fissure. 
In  such  a  case  the  shock  will  be  simultaneous  and  severe  all  along  the 
fissure.  It  is  probable  that  many  so-called  linear  earthquakes  are  thus 
accounted  for. 

The  velocity  of  the  surf  ace- waves,  as  observed  in  many  cases  of  se- 
vere earthquakes,  is  about  twenty  miles  per  minute.  This  accords  well 
with  Mallet's  experiments  in  granite.  In  some  earthquakes  the  ve- 
locity has  been  found  to  be  twelve  to  fifteen  miles  (Mallet's  results  in 
slate),  and  in  some  as  high  as  thirty  to  thirty-five  miles  per  minute. 
In  the  Charleston  earthquake  of  August,  1886,  the  surprising  velocity 
of  eighty  or  even  a  hundred  miles  per  minute  was  observed.  In  some 
slight  shocks,  the  velocity,  as  determined  by  telegraph,  is  estimated  as 
high  as  one  hundred  and  forty  miles  per  minute,  or  12,000  feet  per 
second. 

This  amazing  difference  may  be  thus  explained  :  It  will  be  remem- 
bered that  the  velocity  of  the  surface-wave  is  infinite  at  the  epicentrum, 
and  diminishes,  according  to  a  law  already  discussed,  until  it  reaches, 
or  nearly  reaches,  the  velocity  of  the  spherical  wave.  Now,  if  the 
earthquake-focus  be  comparatively  shallow,  the  initial  velocity  of  the 
surface-wave  very  rapidly  approaches  its  minimum,  and  therefore  the 
observed  velocity  of  the  surface-wave  may  be  taken  as  nearly  the  same 
as  that  of  the  spherical  wave ;  but,  if  the  earthquake  be  very  deep,  the 
diminution,  even  on  a  plane  surface,  is  far  less  rapid ;  and  when  we 
take  into  consideration  the  curvature  of  the  earth-surface,  it  is  evident 
that  the  velocity  of  the  surf  ace- wave  may  be  for  all  distances  much 
greater  than  that  of  the  spherical  wave.  This  would  well  account  for 
velocities  of  thirty  to  thirty-five  miles,  but  not  for  velocities  of  one 
hundred  or  one  hundred  and  forty  miles.  This  latter  is  accounted  for 
by  another  principle. 

These  high  velocities  occur  mostly  in  slight  shocks.  Now,  while 
heavy  shocks  (large  and  high  waves)  break  the  medium  at  every  step  of 
their  passage,  and  are  therefore  retarded,  as  already  explained,  slight 
tremors  (small  and  low  waves)  are  successfully  transmitted  without 
rupture,  and  therefore  run  with  the  natural  velocity  belonging  to  the 
medium,  i.  e.,  the  velocity  of  sound.  Now,  the  velocity  of  sound  in 
granite  is  probably  about  12,000  feet  per  second,  or  one  hundred  and 
forty  miles  per  minute.  In  the  Charleston  earthquake,  however, 
though  a  severe  one,  the  waves  seem  to  have  been  transmitted  with 
nearly  the  normal  velocity  belonging  to  the  medium. 


120 


IGNEOUS  AGENCIES. 


Vorticose  Earthquakes. — In  these  cases  the  ground  is  twisted  or 
whirled  round  and  back,  or  sometimes  ruptured  and  left  in  a  twisted 
condition.  The  most  conspicuous  examples  of  this  kind  of  motion 
occurred  in  the  earthquake  of  Eiobamba,  and  in  the  great  Calabrian 
earthquake  of  1783.  In  this  latter  earthquake  the  Uocks  of  stone 
forming  obelisks  were  twisted  one  on  another ;  the  earth  was  broken 
and  twisted,  so  that  straight  rows  of  trees  were  left  in  interrupted  zig- 
zags. Phenomena  similar  to  some  of  these  were  observed  also  in  the 
California  earthquake  of  1868.  Chimney-tops  were  separated  at  their 
junction  with  roofs,  and  twisted  around  without  overthrow ;  wardrobes 
and  bureaus  turned  about  at  right  angles  to  the  wall,  or  even  with 
their  faces  to  the  wall. 

Explanation. — Some  of  these  effects — such  as  twisting  of  obelisks 
and  chimney- tops,  and  turning  about  of  bureaus,  etc. — may  be  ex- 
plained, as  Lyell  has  shown,  without  any  twisting  motion  of  the  earth 
at  all,  or  any  other  than  the  backward-and-forward  motion  common  to 
all  earthquakes.  Thus,  if  we  place  one  brick  on  another,  and  shake 
them  back  and  forth,  holding  only  the  lower  one,  they  are  almost  cer- 
tain to  be  left  twisted  one  on  the  other.  The  reason  is,  that  the  adhe- 


FIG.  102.— Diagram  illustrating  Beflection  of  Waves— Map  View. 

sion  is  almost  certain  to  be  greater  toward  one  end  than  the  other — the 
center  of  friction  does  not  coincide  with  the  center  of  gravity.  This 
is  the  probable  explanation  of  twisted  obelisks  and  chimney-tops,  etc. 
Also,  the  simple  back-and-forth  shaking  of  a  wardrobe  in  a  diagonal 
direction,  would  almost  certainly  lift  up  one  end  and  swing  it  around. 


EARTHQUAKES.  121 

The  vorticose  motion  in  such  cases  is  probably  not  real,  but  only  ap- 
parent. 

But  there  are  other  cases  of  undoubtedly  real  vorticose  motion ;  as, 
for  example,  straight  rows  of  trees  changed  into  interrupted  zigzags  by 
fissures  and  displacement.  All  such  cases  of  real  twisting  are  prob- 
ably explicable  on  the  principle  of  concurrence  and  interference  of 
waves.  If  two  systems  of  waves  of  any  kind  meet  each  other,  there 
will  be  points  of  concurrence  where  they  re-enforce  each  other,  and 
points  of  interference  where  they  destroy  each  other.  Suppose,  for 
instance,  a  system  of  water-waves,  represented  by  the  double  lines  i,  i 
(Fig.  102),  running  in  the  direction  b  #,  strike  against  a  wall,  w  w : 
the  waves  would  be  reflected  in  the  direction  c  c,  and  are  represented 
by  the  single  lines  r,  r.  Then,  if  the  lines  represent  crests,  and  the 
intervening  space  the  troughs,  at  the  places  marked  with  crosses  and 
dots  there  would  be  concurrence,  and  therefore  higher  crests  and  deeper 
troughs,  while  at  the^  points  indicated  by  a  dash  there  would  be  inter- 
ference and  mutual  destruction,  and  therefore  smooth  water.  The  same 
takes  place  in  earth- waves.  If  two  systems  of  earth-waves  meet  and 
cross  each  other,  we  must  have  points  of  concurrence  and  interference 
in  close  proximity.  The  ground,  therefore,  will  be  thrown  into  violent 
agitation — points  in  close  proximity  moving  in  opposite  directions 
(twisting).  If  the  motion  be  sufficient  to  rupture  the  earth,  restoration 
is  not  made  by  counter-twisting,  and  the  earth  is  left  in  a  displaced 
condition. 

The  causes  of  interference  may  be  various — sometimes  by  the  nor- 
mal and  transverse  waves  combining  differently  so  as  to  produce  motion 
in  different  directions  in  contiguous  places ;  sometimes  by  difference  of 
velocity  of  waves,  already  explained,  by  which  some  overrun  others, 
concurring  and  interfering;  more  often  it  is  the  result  of  reflection 
from  surfaces  of  different  elasticity.  For  example,  it  is  well  known 
that  the  most  violent  effects  of  earthquakes,  especially  twisting  of  the 
ground,  usually  occur 
near  the  junction  of 
the  softer  strata  of  the 
plains  with  the  harder 
and  more  elastic  strata 
of  the  mountains.  Now, 
suppose  from  a  shock 
at  X  (Fig.  103)  a  sys- 
tem of  earth  -  waves  FlG  103. -Reflection  of  Earthquake- Waves-Section. 

should    emerge    at    «, 

and  run  as  a  surface- wave  toward  the  mountain  m.  The  waves,  strik- 
ing the  hard,  elastic  material  m,  would  be  partly  transmitted  and 
partly  reflected.  The  reflected  waves  running  in  the  direction  of  the 


122  IGNEOUS  AGENCIES. 

arrow  r,  would  meet  the  advancing  incident  waves  moving  in  the  di- 
rection of  the  arrow  i,  and  concurrence  and  interference  would  be  in- 
evitable.* 

Minor  Phenomena. — Not  only  the  several  kinds  of  earthquakes,  but 
many  of  the  minor  phenomena  are  explained  by  the  wave-theory. 

1.  Sounds. — These  are  usually  described  as  a  holloiv  rumbling,  roll- 
ing, or  grinding ;  sometimes  as  clashing,  thundering,  or  cannonading. 
They  are  probably  produced  by  rupture  of  the  earth  at  the  origin,  and 
by  the  passage  of  the  wave  through  the  imperfectly  elastic  rocky  me- 
dium breaking  the  medium  and  grinding  the  broken  parts  together. 
But  what  is  especially  noteworthy  is,  that  these  sounds  precede  as  well 
as  accompany  the  shocks.     In  every  earthquake  there  are  transmitted 
waves  of  every  variety  of  size.     The  great  waves  are  sensible  as  shocks, 
or  jars,  or  tremors ;  the  very  small  waves,  too  small  to  be  appreciated 
as  tremors,  are  heard  as  sounds.     But,  as  already  explained,  these  last 
run  with  greater  velocity  in  an  imperfectly  coherent  medium  like  the 
earth,  and  therefore  arrive  sooner  than  the  great  waves,  which  consti- 
tute the  shock.     The  same  was  observed  in  Mallet's  experiments. 

2.  Motion. — As  to  direction,  the  observed  motion  is  sometimes  verti- 
cally up  and  down,  sometimes  horizontally  back  and  forth,  and  some- 
times oblique  to  the  horizon.     Almost  always  a  rocking  motion,  i.  e.,  a 
leaning  of  tall  objects  first  in  one  direction  and  then  in  the  other,  is 
observed.     As  to  violence  or  velocity  of  motion,  this  is  sometimes  so 
great  that  objects  are  thrown  into  the  air,  and  whole  cities  are  shaken 
down  as  if  they  were  a  mere  collection  of  card-houses  ;  while  in  other 
cases  only  a  slow  swinging,  or  heaving,  or  gentle  rocking,  is  observed. 

If  we  confine  our  attention  to  the  principal  or  normal  wave,  the 
difference  in  direction  is  wholly  due  to  the  position  of  the  observer.  At 
the  epicentrum  it* is  of  course  vertical,  and  thence  it  becomes  more  and 
more  oblique,  until  at  great  distances  it  is  usually  horizontal.  The 
violence  of  the  shock  or  velocity  of  ground-motion  depends  partly  upon 
the  violence  of  the  original  concussion,  and  partly  on  the  distance  from 
the  origin  or  focus.  This  velocity  of  the  ground-motion  must  not  be 
confounded  with  the  velocity  of  the  wave  already  discussed.  The  lat- 
ter is  the  velocity  of  transit  from  place  to  place ;  the  former  is  the 
velocity  of  oscillation  up  and  down,  or  back  and  forth.  The  velocity 
of  oscillation  has  no  relation  to  the  velocity  of  transit,  but  depends 
only  on  the  height  of  the  wave,  which  constantly  diminishes  and  be- 
comes finally  very  small,  though  the  velocity  of  transit  remains  the 
same,  and  always  enormously  great.  The  rocking -motion  is  also  easily 

*  For  an  excellent  discussion  of  the  effects  of  interference  of  earth- waves,  see  a  mem- 
oir by  Prof.  John  Milne,  Transactions  of  the  Seismological  Society  of  Japan,  vol.  i,  Part 
II,  p.  82. 


EARTHQUAKES. 


123 


explained.  A  series  of  waves,  somewhat  similar  in  form  to  water-waves 
(though  differing  in  nature),  actually  passes  beneath  the  observer.  Of 
course,  when  an  object  is  on  the  front-slope,  it  will  lean  in  the  direction 
of  transit ;  and  when  on  the  hind-slope,  in  the  contrary  direction. 

3.  Circle  of  Principal  Destruction. — In  some  earthquakes  a  certain 
zone  at  considerable  distance  from  the  point  of  first  emergence  (epicen-^ 
trum)  has  been  observed,  within  which  the  destruction  by  overthrow  is 
very  great, "and  beyond  which  it  speedily  diminishes.     This  has  been 
called  the  circle  of  principal  destruction  or  overthrow.     It  is  thus  ex- 
plained :  The  overthrow  of  buildings  depends  not  so  much  on  the 
amount  of  oscillation  as  upon  the  horizontal  element  of  the  oscillation. 
Now,  the  whole  amount 

of  oscillation  is  greatest  a ' 

at    the    point    of   first 

,       , 

emergence,  and  de- 
creases outward  ;  but 
the  horizontal  element 
is  nothing  at  #,  and  in- 
creases as  the  cosine  of 
the  angle  of  emergence. 
Therefore,  under  the  in- 
fluence of  these  two 
conditions,  one  decreas- 
ing the  whole  oscillation,  the  other  increasing  the  horizontal  element  of 
that  oscillation,  it  is  evident  that  there  will  be  a  point  on  every  side,  or, 
in  other  words,  a  circle,  where  the  horizontal  element  will  be  a  maximum. 
This  is  shown  in  Fig.  104,  in  which  a  «',  b  #',  c  c',  etc.,  are  the  de- 
creasing oscillation,  and  ft  V\  c  c",  are  the  horizontal  element.  This 
reaches  a  maximum  at  c.  It  has  been  found  by  mathematical  calcula- 
tion, based  upon  the  supposition  that  the  whole  oscillation  varies  in- 
versely as  the  square  of  the  distance  from  JT,  that  the  horizontal  ele- 
ment will  be  a  maximum  when  the  angle  of  emergence  is  54°  44'.  By 
determining  by  observation  the  circle  of  principal  disturbance,  it  is 
easy  to  calculate  the  depth  a  X  of  the  focus,  for  it  will  be  the  apex  of 
a  cone  whose  base  is  that  circle,  and  whose  apical  angle  is  70°  32'.* 

4.  Shocks  more  severely  felt  in  Mines. — It  has  been  sometimes  ob- 
served that  shocks  are  distinctly  felt  in  mines  which  are  insensible  at 
the  surface.     This  is  probably  explained  as  follows :  Let  8  S  (Fig.  105) 
be  the  surface  of  the  ground ;  and  let  a  I)  represent  hard,  elastic  strata, 
covered  with  loose,  inelastic  materials,  c  c.     Now,  if  a  series  of  waves 
come  in  the  direction  of  the  arrows  d  d,  and,  passing  through  a  b  on 
their  way  to  the  surface,  strike  upon  the  lower  surface  of  c  c,  a  portion 


FIG.  104.~Diagram  illustrating  Circle  of  Principal  Disturbance. 


*  Mallet's  Report  for  1858,  p.  101. 


124 


IGNEOUS  AGENCIES. 


FIG.  105.— Shocks  in  Mines. 


would  reach  the  surface  by  refraction,  but  a  portion  would  be  reflected 
and  return  into  a  #,  concurring  and  interfering  with  the  advancing/ 
waves,  and  producing  great  commotion  in  these  strata. 

5.  Shocks  less  severe  in  Mines. — This  case  is  probably  more  common 
than  the  last.     It  was  notably  the  case  in  the  earthquake  of  1872  in 

Inyo  County,  Califor- 
nia. While  the  sur- 
face was  severely 
shaken,  many  houses 
destroyed,  and  large 
fissures  formed  in  the 
earth,  the  miners,  sev- 
eral hundred  feet  be- 
low the  surface  in  the 
hard  rock,  scarcely 

felt  it  at  all.  This  is  probably,  at  least  partly,  explained  as  follows : 
As  long  as  the  wave  travels  within  the  earth,  motion  of  the  particles  is 
restrained  by  the  work  of  elastic  compression ;  but,  as  soon  as  the  sur- 
face is  reached,  the  motion  becomes  free,  and  the  velocity  of  shock  is  far 
greater  than  before,  often  so  great  as  to  throw  bodies  high  in  the  air. 
The  phenomenon  is  exactly  like  that  in  the  familiar  experiment  of  the 
ivory  balls :  when  the  first  in  the  series  is  struck,  an  elastic  wave  of 
compression  passes  through  all,  but  only  the  last  one  moves. 

6.  Bridges. — In  a  manner  somewhat  similar  are  to  be  accounted 
for  the  phenomena  of  bridges.     In  the  earthquake  regions  of  South 
America  there   are 

certain  favored 
spots,  often  of  small 
extent,  which  are 
partially  exempt 
from  the  shocks 
which  infest  the 
surrounding  coun- 
try. The  earth- 
quake-wave seems  to  pass  under  them  as  under  a  bridge,  to  reappear 
again  on  the  other  side.  The  mere  inspection  of  Fig.  106  will  explain 
the  probable  cause  of  this  exemption,  viz. :  reflection  from  the  under 
surface  of  an  isolated  mass  of  soft,  inelastic  strata,  c  c. 

7.  Fissures. — The  ground-fissures,  so  commonly  produced  by  earth- 
quakes, are  sometimes  of  the  nature  of  the  great  fissures  of  the  crust, 
which  are  the  probable  cause  of  earthquakes.     Such  great  fissures  are 
usually  wholly  beneath  the  surface  at  great  depth,  but  sometimes  may 
break  through  and  appear  on  the  surface.     This  is  certainly  the  case 
when  decided  faults  occur  with  elevation  or  depression  of  large  tracts 


FIG.  106. 


EARTHQUAKES   ORIGINATING  BENEATH   THE   OCEAN.  125 

of  land.  But  the  surf  ace- fissures  so  frequently  described,  small  in  size, 
very  numerous,  and  running  in  all  directions,  have  an  entirely  different 
origin.  They  are  evidently  produced  by  the  shattering  of  the  softer, 
more  incoherent,  and  inelastic  surface-soil,  and  by  the  passage  of  the 
earth-wave.  Even  the  more  elastic  underlying  rock  is  broken  by  the 
same  cause,  but  to  a  much  less  extent. 

Earthquakes  originating  beneath  the  Ocean. 

"We  have  thus  far  spoken  of  earthquakes  originating  beneath  the 
land-surface.  But  three  fourths  of  the  earth-surface  is  covered  by  the 
sea ;  and  we  have  already  seen  that  other  forms  of  igneous  agency  are 
most  abundant  in  and  about  the  sea.  As  we  might  expect,  therefore, 
the  greater  number  of  earthquake-shocks  occur  beneath  the  sea-bed. 
It  is  worthy  of  remark  that  this  is  especially  true  of  the  sea-bed  imme- 
diately bordering  the  continents.  In  such,  the  phenomena  already 
described  are  often  complicated  by  the  addition  of  the  "  Great  Sea- 
Wave." 

Suppose,  then,  an  earthquake-shock  to  occur  beneath  the  sea-bed  ; 
the  following  waves  will  be  formed :  1.  As  before,  a  series  of  elastic 
spherical  waves  will  spread  from  the  focus,  until  they  emerge  on  the 
sea-bed.  2.  As  before,  a  series  of  circular  surf  ace- waves,  the  outcrop  of 
the  spherical  waves,  will  spread  on  the  sea-bottom  until  they  reach  the 
nearest  shore,  and  perhaps  produce  destructive  effects  there.  3.  On 
the  back  of  this  submarine  earth- wave  is  carried  a  corresponding  sea- 
wave.  This  is  called  the  "forced  sea-ivave" since  it  is  not  a  free  wave, 
but  a  forced  accompaniment  of  the  ground-wave  beneath.  It  reaches 
the  shore  at  the  same  time  as  the  earth-wave.  It  is  of  little  impor- 
tance. 4.  In  addition  to  all  these  is  formed  the  great  sea-wave;  or 
tidal  wave,  as  it  is  sometimes,  but  wrongly,  called. 

Great  Sea- Wave. — This  common  and  often  very  destructive  accom- 
paniment of  earthquakes  is  formed  as  follows :  The  sudden  upheaval  of 
the  sea-bed  lifts  the  whole  mass  of  superincumbent  water  to  an  equal 
extent,  forming  a  huge  mound.  This  movement  of  the  sea-bed  is  not 
due  to  the  mere  emergence  of  the  earth-wave,  for  this  is  far  too  small  to 
produce  such  effects;  but  is  due  to  bodily  movement  of  the  earth-crust 
by  displacement  of  a  fissure  which,- as  we  have  seen,  is  the  usual  cause 
of  earthquakes.  The  falling  again  of  this  water  as  far  below  as  it  was 
before  above  its  natural  level  generates  a  circular  wave  of  gravity, 
which  spreads  like  other  water-waves,  maintaining  its  original  wave- 
length, but  gradually  diminishing  its  wave-height  until  it  becomes 
insensible.  Usually,  a  series  of  such  waves  is  formed.  These  waves  are 
often  100  to  200  miles  across  their  base  (wave-length)  and  fifty  to 
sixty  feet  high  at  their  origin.  Their  destructive  effects  may  be 
inferred  from  the  enormous  quantity  of  water  they  contain.  In  the 


126  IGNEOUS  AGENCIES. 

open  sea  they  create  no  current,  and  are  not  even  perceived;  but, 
when  they  touch  bottom  near  shore,  they  rush  forward  as  great 
breakers  fifty  or  sixty  feet  high,  sweeping  away  everything  in  their 
course. 

Being  waves  of  gravity,  their  velocity,  though  very  great  on  ac- 
count of  their  size,  is  far  less  than  that  of  the  earth- waves,  and  they 
reach  the  neighboring  shore,  therefore,  some  time  later,  and  often 
complete  the  destruction  commenced  by  the  earth-waves. 

Examples  of  the  Sea-Wave. — In  the  great  earthquake  which  de- 
stroyed Lisbon  in  1755,  the  epicentrum  was  on  the  sea-bed  fifty  or  more 
miles  off  the  coast  of  Portugal.  From  this  point  the  surface  earth- 
waves  spread  along  the  sea-bottom  until  they  reached  shore.  It  was 
the  arrival  of  these  waves  which  destroyed  Lisbon.  About  a  half-hour 
later,  when  all  had  become  quiet,  several  great  sea-waves,  one  of  them 
sixty  feet  high,  came  rushing  in,  deluging  the  whole  coast  and  com- 
pleting the  destruction  commenced  by  the  earth- waves.  This  wave  was 
thirty  feet  high  at  Cadiz,  eighteen  feet  at  Madeira,  and  five  feet  on  the 
coast  of  Ireland.  It  was  sensible  on  the  coast  of  Norway,  and  even  on 
the  coast  of  the  West  Indies,  after  having  crossed  the  whole  breadth 
of  the  Atlantic. 

In  1854  a  great  earthquake  shook  the  coast  of  Japan.  Its  focus  was 
evidently  beneath  the  sea-bed  some  distance  off  the  coast,  for,  in  about 
a  half-hour,  a  series  of  water-waves  thirty  feet  high  rushed  upon  shore 
and  completely  swept  away  the  town  of  Simoda.  From  the  same  cen- 
ter the  waves,  of  course,  spread  in  the  contrary  direction,  traversed  the 
whole  breadth  of  the  Pacific,  and  in  about  twelve  and  a  quarter  hours 
struck  on  the  coast  of  California  at  San  Francisco,  and  swept  down  the 
coast  to  San  Diego.  These  waves  were  thirty  feet  high  at  Simoda,  fif- 
teen feet  high  at  Peel's  Island,  about  1,000  miles  off  the  coast  of  Japan, 
0-65  feet,  or  eight  inches,  high  at  San  Francisco,  and  six  inches  at  San 
Diego.* 

On  the  13th  of  August,  1868,  a  great  earthquake  desolated  the  coast 
of  Peru.  Its  focus  was  evidently  but  a  little  way  off  shore,  for  in  less 
than  a  half-hour  a  series  of  water-waves  fifty  or  sixty  feet  high  rushed 
in  and  greatly  increased  the  devastation  commenced  by  the  earth- waves. 
These  waves  reached  Coquimbo,  800  miles  distant,  in  three  hours ; 
Honolulu,  Sandwich  Islands,  5,580  miles,  in  twelve  hours ;  the  Japan 
coast,  over  10,000  miles,  the  next  day.  They  were  also  observed  on 
the  coast  of  California,  Oregon,  and  Alaska,  over  6,000  miles  in  one 
direction,  and  on  the  Australian  coast,  nearly  8,000  miles  in  another 
direction.  This  series  of  waves  was  distinctly  sensible  at  a  distance  of 
nearly  half  the  circumference  of  the  earth.  Had  it  not  been  for  the 

*  Report  of  Coast  Survey  for  1862. 


EARTHQUAKES  ORIGINATING  BENEATH   THE   OCEAN.  127 

barrier  of  the  South  American  Continent,  it  would  have  encircled  the 
globe.* 

Many  other  earthquake  sea- waves  have  been  observed  and  recorded 
by  tidal  gauges,  especially  these  of  the  Iquique  earthquake  of  May, 
1877,  and  the  waves  caused  by  the  great  eruption  of  Krakatoa,  August,- 
1883. 

There  are  several  points  in  the  above  description  which  we  must 
very  briefly  explain : 

1.  The  velocity  of  these  great  sea- waves,  though  less  than  that  of 
the  earth-waves,  is  still  very  great  in  comparison  with  ordinary  sea- 
waves.     The  waves  of  the  Japan  earthquake  crossed  the  Pacific  to  San 
Francisco,  a  distance  of  4,525  miles,  in  a  little  more  than  twelve  hours, 
and  therefore  at  a  rate  of  370  miles  per  hour,  or  over  six  miles  per 
minute.     The  waves  of  the  South  American  earthquake  of  1868  ran  to 
the  Hawaiian  Islands  at  a  rate  of  454  miles  per  hour.     This  amazing 
velocity  is  the  result  of  the  great  size  of  these  waves  ;  for  the  velocity 
of  water-waves  varies  as  the  square  root  of  the  wave-length  (v  oc  VL). 

2.  The  size  of  these  great  waves  is  determined  by  multiplying  the 
time  of  oscillation  by  the  velocity,  on  the  well-known  principle  that 
every  kind  of  wave  runs  its  own  length  during  the  time  of  one  com- 
plete oscillation.     The  velocity  is  obtained  by  observing  the  time  at 
different  points.     The  time  of  oscillation  is  determined  by  means  of 
tidal  gauges.     The  tidal  gauges  established  by  the  Coast  Survey  on  the 
Pacific  coast  showed  that  the  time  of  oscillation  of  the  larger  waves  of 
the  Japan  earthquake  was  about  thirty-three  (thirty- one  to  thirty-five) 
minutes.     This  would  give  a  wave-length  of  a  little  over  200  miles.     It 
is  probable  that  the  wave-length  in  the  case  of  the  South  American 
earthquake  was  at  least  equally  great. 

3.  The  distance  to  which  the  sea- waves  run  is  far  greater  than  that 
of  the  earth- waves.     The  former  is  distinctly  sensible  for  10,000  miles ; 
the  latter  very  rarely  more  than  a  few  hundreds.     There  are  two  rea- 
sons for  this :  1.  All  waves  diminish  in  oscillation  (wave-height)  as  they 
spread  from  the  origin,  because  the  quantity  of  matter  successively 
involved  in  the  oscillation  constantly  increases.     But  in  the  one  case 
the  matter  involved  lies  in  the  circumference  of  a  circle ;  in  the  other, 
in  the  surface  of  a  sphere ;  therefore,  the  one  increases  as  the  distance, 
the  other  as  the  square  of  the  distance.     Therefore,  the  decrease  of  os- 
cillation (height  of  wave)  is  far  less  rapid  for  water-waves  than  for  elas- 
tic spherical  waves.     2.  A  still  more  effective  reason  is  this :    Water- 
waves  run  in  a  perfectly  homogeneous  medium,  and  therefore  diminish 
only  according  to  the  regular  law  just  stated ;  but  the  earth-waves  run 
in  an  heterogeneous,  imperfectly  elastic,  and  imperfectly  coherent  me- 

*  Report  of  Coast  Survey  for  1869. 


128  IGNEOUS  AGENCIES. 

dium,  and  therefore  they  are  rapidly  quenched  and  dissipated  by  re- 
peated refractions  and  reflections,  and  by  repeated  fractures  of  the 
medium  and  thus  changed  into  other  forms  of  force,  as  heat,  electricity, 
etc.  Were  it  not  for  this,  the  destructive  eifects  of  earthquakes  would 
be  far  more  extensive. 

4.  We  have  said  the  wave-length  remains  unchanged.    This  length, 
therefore,  represents  the  diameter  of  the  original  water-mound,  and 
therefore  of  the  original  sea-bottom  upheaval.     In  the  Japan  earth- 
quake this  was  200  miles  across.     This  shows  the  grand  scale  upon 
which  earthquake-movements  take  place. 

5.  Earthquake  sea-waves  differ  from  all  other  sea-waves  in  that 
their  great  size  makes  them  drag  bottom  even  in  open  deep  sea.     In 
their  case,  therefore,  the  velocity  depends  not  only  on  the  wave-length, 
but  also  on  the  depth  of  the  sea.     Knowing  the  size  (wave-length)  of 
these  waves,  and  therefore  what  ought  to  be  their  free  velocity r,  and 
also  knowing  their  actual  velocity  by  observation,  the  difference  gives 
the  retardation  by  dragging ;  and  by  the  retardation  may  be  calculated 
the  mean  depth  of  the  ocean  traversed.     In  this  way  it  has  been  de- 
termined that  the  mean  depth  of  the  Pacific  between  Japan  and  San 
Francisco  is  12,000  feet,  and  between  Peru  and  Honolulu,  Sandwich 
Islands,  18,500  feet.     The  great  importance  of  such  results  is  obvious. 

Depth  of  Earthquake- Focus. 

The  great  obscurity  which  hangs  about  the  subject  of  the  interior 
condition  of  the  earth  and  the  ultimate  cause  of  igneous  agencies  ren- 
ders any  positive  knowledge  on  these  subjects  of  peculiar  interest.  There 
can  be  little  doubt  that  the  phenomena  of  earthquake- waves,  their  form, 
their  velocity,  their  angle  of  emergence,  etc.,  if  once  thoroughly  under- 
stood, would  be  a  most  delicate  index  of  this  condition,  and  a  powerful 
means  of  solving  many  problems  which  now  seem  beyond  the  reach  of 
science.  Among  problems  of  this  kind  none  is  more  important,  and  at 
the  same  time  more  capable  of  solution,  than  the  depth  of  the  origin  of 
earthquakes,  and  therefore  presumably  of  volcanoes. 

Seismographs. — The  most  direct  way  of  determining  the  depth  of 
an  earthquake-focus  is  by  means  of  well-constructed  seismographs. 
These  are  instruments  for  recording  earthquake-phenomena.  They 
are  of  infinite  variety  of  forms,  depending  partly  upon  the  facts  de- 
sired to  be  recorded,  and  partly  upon  the  mode  of  record.  As  examples 
we  will  mention  only  two  : 

An  excellent  instrument  for  recording  slight  tremors  is  one  invented 
and  used  by  Prof.  Palmieri,  of  the  Vesuvian  Observatory.  It  consists 
of  a  telegraphic  apparatus  with  the  usual  paper-slip  and  stile.  The 
paper-slip,  accurately  divided  into  hours,  minutes,  and  seconds,  travels 
at  a  uniform  rate  by  means  of  clock-work.  The  battery- circuit  is  closed 


DEPTH  OF  EARTHQUAKE-FOCUS. 


129 


and  opened,  and  the  recording  stile  worked  by  the  shaking  of  a  metallic 
bob,  hung  by  a  delicate  spiral  spring  above  a  mercury-cup ;  the  shak- 
ing of  the  bob  being  determined  by  the  tremor  of  the  earth.  Such  an 
instrument  records  the  exact  moment  of  occurrence  of  earthquake- 
shocks,  however  slight ;  also,  the  moment  of  passage  of  every  wave  and 
its  time  of  oscillation ;  and  if  there  be  more  than  one  such  instrument, 
the  moment  of  occurrence  at  different  places  gives  the  velocity  of  the 
surf  ace- wave  v'. 

If  we  desire  to  record  not  only  the  time  but  also  the  character  of 
the  earth-movement,  then  a  different  kind  of  seismograph  is  neces- 
sary. The  principle  of  all  these  is  the  principle  of  a  pendulum.  If 
we  have  a  pendulum  with  a  heavy  bob  swinging  freely,  when  an  earth- 
quake arrives,  the 
bob  will  stand  still, 
while  the  earth 
moves  beneath  it. 
This  relative  move- 
ment of  the  pend- 
ulum may  be  re- 
corded by  suitable 
device.  But  an 
ordinary  freely 
swinging  pendu- 
lum moves  often 
too  largely,  and 
continues  its  move- 
ment after  the  ces- 
sation of  the  cause. 
What  we  want  is  a 
pendulum  which 
will  stand  indiffer- 
ently in  any  posi- 
tion (astatic).  One 
of  the  best  forms 
of  instrument  yet 
devised  is  that  of 
Prof.  Ewing  (Fig. 
107).  It  consists 
essentially  of  three  pendulums  swinging  in  the  manner  of  a  bracket  or 
a  gate,  and  placed  in  three  rectangular  planes;  (1)  vertical  north  and 
south,  a  ;  (2)  vertical,  east  and  west,  b;  and,  (3)  horizontal,  c.  The 
horizontal  one  is  retained  in  position  by  sensitive  spiral  springs.  Stiles 
are  fixed  to  these  pendulums  in  such  wise  as  to  record  on  a  circular 
smoked  glass  plate  rotating  in  a  horizontal  plane.  No.  1  records  the 
9 


FIG  107  — Ewlng's  Seismograph  :  a  and  b.  horizontally  oscillating 
pendulum;  c,  vertically  oscillating  pendulum;  cl,  driving  clock; 
e,  lime-recording  clock.  (Taken  from  a  photograph  of  one  at  the 
University  of  California.) 


130 


IGNEOUS  AGENCIES. 


east-and-west  movement,  No.  2  the  north-and-south  movement,  and 
No.  3  the  up-and-down  movement.  A  clock  is  set  agoing  by  the  ar- 
rival of  the  earth  waver  and  afterward  marks  seconds  on  the  revolving 

smoked  glass  disk.  Fig.  108  represents  a 
portion  of  such  record.  These  three  rec- 
ords may  be  combined  so  as  to  show  the 
actual  amount  and  direction  of  the  earth- 
movement  (Fig.  99,  p.  117). 

The  important  facts  recorded  by  this 
instrument  are :  1.  The  instant  of  trans- 
it;  2.  The  direction  of  transit;  3.  The 
direction  of  oscillation,  or  angle  of  emer- 
gence ;  4.  The  amount  of  oscillation. 
From  these  elements  (if  we  have  several 
seismographs  scattered  about  the  country) 
may  be  calculated :  1.  The  velocity  of 
transit;  2.  The  position  of  the  focus  ;  3. 
Perhaps  the  form  of  the  focus,  whether 
point  or  fissure ;  4.  The  force  of  the  orig- 
inal concussion.  The  most  important  of 
these  are  the  position  and  depth  of  the 
focus. 

The  Determination  of  the  Epicentrum. 
— A  good  seismograph,  or  a  number  of 
these,  will  give  the  direction  of  transit  of  the  surface-wave.  If  in 
this  way,  or  even  by  rougher  methods,  we  get  a  number  of  these  sur- 
face-lines of  transit,  by  fol- 
lowing these  back  we  get  the 
epicentrum  at  their  intersec- 
tion. This  is  Mallet's  meth- 
od. Or  if,  by  means  of  many 
seismographs  giving  time  of 
transit,  or  even  by  observa- 
tories or  stations  of  any  kind 
with  accurate  clocks,  we  get 
several  points  of  simultane- 
ous arrival  of  the  wave,  then 
by  drawing  a  curve  through 
these  points  we  have  a  coseis- 
mal curve.  A  perpendicular 
drawn  from  the  middle  point  FlG  m_cosei6mai  Lines. 

of  the  line  joining  any  two  of 

these  points  will  pass  through  the  epicentrum,  and  two  such  perpen- 
diculars would  determine  its  position.  Fig.  109  represents  coseismal 


A-7 


FIG.  108. — Record  of  a  Ewing's  Seismo- 
graph: a,  east-and-west  motion;  b, 
north-and-south  motion;  c,  up-and- 
down  motion  (after  Sekiya). 


DEPTH   OF  EARTHQUAKE-FOCUS.  131 

curves,  and   #,  c,  d,  three  points  on  the  curve ;   a  is  the  epicentrum. 
This  is  Seebach's  method. 

Determination  of  the  Focus. — The  normal  wave  is  a  wave  of  longi- 
tudinal oscillation.  The  direction  of  oscillation,  therefore,  is  the  same 
as  the  direction  of  transmission  (wave-path),  which  is  the  radius  of  the 
agitated  sphere.  If,  therefore,  the  direction  of  the  ground-motion  be 
followed  into  the  earth,  it  carries  us  back  along  the  wave-path  to  its 
origin,  the  focus.  Two  such  wave-paths  by  their  intersection  would 
determine  its  position.  Thus,  in  Fig.  110,  if  c  and  b  be  the  position  of 
two  seismomet-  §  c  1*  CL  s 

ric  observato- 
ries, the  angles  of  emergence, 
x  c  a  and  x  b  «,  being  given  by 
observation,  and  the  distance, 
c  b,  being  known,  we  have  all 
the  elements  necessary  to  de-  Fio  no 

termine  either  by  calculation 

or  by  accurate  plotting  the  wave-paths  c  x  and  b  x,  and  their  point  of 
intersection  x,  and  therefore  of  the  depth  a  x. 

We  have  assumed  the  earth-waves  as  normal.  We  are  justified  in 
so  doing,  because  this  is  the  most  decided  wave,  and  soon  outruns  the 
transverse  wave. 

Although  seismometers,  such  as  we  have  described,  are  necessary 
for  accurate  results  from  few  observations,  yet  by  multiplying  the  ob- 
servations, even  by  rough  methods,  approximative  results  may  be  ob- 
tained. We  will  mention  several  examples; 

In  1857  a  terrible  earthquake  shook  the  territory  of  Naples,  destroy- 
ing many  towns  and  villages,  and  killing  about  10,000  people.  The 
scene  of  destruction  was  visited  soon  after  by  Mr.  Mallet.  By  careful 
examination  of  overthrown  objects,  many  lines  of  transit  of  the  surface- 
wave  were  determined,  which,  protracted,  carried  him  with  considera- 
ble certainty  to  the  epicentrum ;  similarly  many  lines  of  emergence,  or 
paths  of  the  spherical  wave,  protracted  back,  conducted  to  the  focus. 
This  focus  was  determined  to  be  not  a  point,  but  a  fissure,  nine 
miles  long  and  through  three  miles  of  solid  rock.  The  center  of  this 
rent  was  about  six  miles  beneath  the  surface.*  By  somewhat 
similar  methods  the  focus  of  the  Japan  earthquake  of  February 
22,  1880,  was  found  by  Milne  to  be  only  three  to  five  miles  deep.f 
By  a  different  and  new  method,  viz.,  the  laiv  of  decrease  of  intensity 
of  the  shock-motion,  the  focus  of  the  Charleston  earthquake  of  Au- 
gust, 1886,  was  found  by  Captain  Duttou  to  be  about  twelve  miles 

*  Mallet,  Principles  of  Seismology. 

f  Seismological  Society  of  Japan,  vol.  i,  Part  II,  p.  1. 


132  IGNEOUS  AGENCIES. 

deep.*  Both  of  these  earthquakes  also  seem  to  have  originated  in  a 
fissure. 

In  1874  a  not  very  severe  earthquake  shook  central  Germany.  It 
has  been  thoroughly  investigated  by  Seebach.  The  epicentrum  was 
determined  with  great  precision  by  erecting  perpendiculars  to  the  bi- 
sected chords  of  the  coseismal  curves.  "  The  focus  was  determined  as  a 
rent  through  four  miles  of  rock,  the  center  of  the  rent  being  nine  or 
ten  miles  in  depth,  f 

The  velocity  of  transit  of  the  waves  of  the  Naples  earthquake  was 
860  feet  per  second,  or  between  nine  and  ten  miles  per  minute ;  that  of 
the  earthquake  of  middle  Germany  was  about  twenty-eight  miles  per 
minute.  The  velocity  of  transit  in  the  case  of  the  Charleston  earth- 
quake is  estimated  as  high  as  one  hundred  or  even  one  hundred  and 
eighty  miles  per  minute. 

There  have  been  many  attempts  to  determine  the  depth  of  earth- 
quakes by  other  methods,  especially  by  using  the  relative  velocities  of 
the  spherical  and  the  surface  waves  as  a  means  of  getting  the  angle  of 

emergence  (sec.  E=  —  J  ;  but  such  a  method   is  evidently  valueless, 

because  the  velocity  of  the  spherical  wave  (v)  is  not  constant.); 

Effect  of  the  Moon  on  Earthquake  -  Occurrence. — By  an  extensive 
comparison  of  the  times  of  occurrence  of  several  thousand  earthquakes 
with  the  positions  of  the  moonr  Alexis  Perrey  has  made  out  with  some 
probability  the  following  laws :  1.  Earthquakes  are  a  little  more  fre- 
quent when  the  moon  is  on  the  meridian  than  when  she  is  on  the 
horizon.  2.  They  are  a  little  more  frequent  at  new  and  full  moon 
(syzygies)  than  at  half-moon  (quadratures).  3.  They  are  a  little  more 
frequent  when  the  moon  is  nearest  the  earth  (perigee)  than  when  she 
is  farthest  off  (apogee).  Now,  if  these  laws  are  really  true,  it  would 
seem  that  there  is  a  slight  tendency  for  earthquakes  to  follow  the  law 
of  tides  :  for  the  first  law  gives  the  time  of  flood-tide,  and  the  second 
and  third  the  times  of  highest  flood-tide.  It  would  seem,  therefore, 
that  the  attraction  of  the  sun  and  moon  has  a  perceptible  effect  in 
determining  the  time  of  occurrence  of  earthquakes.  Many  geologists 
regard  these  laws,  if  established,  as  conclusive  proof  of  the  general 
fluid  condition  of  the  earth  beneath  a  comparatively  thin  crust.  This 
interior  liquid  they  suppose  to  be  influenced  by  the  tide-generating 
forces  of  the  sun  and  moon;  but,  if  this  were  true,  the  effect  ought 
to  be  far  greater  than  we  find  it.  Whatever  be  the  interior  condition 

*  Science,  vol.  ix,  p.  489,  1887.  f  Seebach,  Das  Mittel  Deutsche  Erdbeben. 

J  But  although  it  is  impossible  thus  to  find  the  depth  of  the  focus  directly,  yet  indi- 
rectly it  may  be  found,  as  Seebach  has  shown,  by  the  rate  of  decrease  of  the  velocity  of 
the  surf  ace- wave  (v').  The  deeper  the  focus,  the  slower  the  rate  of  decrease  from  infinity 
at  the  epicentrum. 


ELEVATION  AND    DEPRESSION   OF  EARTH'S  CRUST.  133 

of  the  earth,  the  effect  of  the  moon  on  the  meridian  would  be  to  assist, 
and  on  the  horizon  to  repress,  any  force  whatsoever  tending  to  break 
up  the  crust  of  the  earth  and  to  produce  an  earthquake. 

Relation  of  Earthquake-Occurrence  to  Seasons  and  Atmospheric 
Conditions. — By  extensive  comparison  of  earthquake-occurrence  with 
the  seasons,  it  has  been  shown  that  they  are  a  trifle  more  frequent  in 
winter  than  in  summer.  Constructing  a  curve  representing  the  annual 
variation  of  earthquake-intensity,  this  curve  rises  to  its  maximum  in 
January  and  sinks  to  its  minimum  in  July.  But  the  difference  is 
small. 

Prof.  Knott  has  recently  suggested  what  seems  a  possible  expla- 
nation of  this,  at  least  for  Japan,  where  this  relation  is  quite  marked. 
During  winter,  there  is  high  barometer — i.  e.,  great  atmospheric  pressure 
over  the  whole  of  Northern  Asia  (Siberia),  and  low  barometer  over 
equatorial  Pacific.  In  addition  to  this,  the  heavy  winter  snow-fall 
greatly  increases  the  pressure  over  Siberia.  In  summer,  the  condition 
of  things  is  reversed — the  barometer  is  low  and  the  snow  is  removed 
over  Siberia,  and  the  barometer  is  high  over  mid- Pacific.  This 
change  of  excess  of  pressure  from  a  large  land-area  to  a  large  ocean- 
area  back  and  forth,  must  tend  to  fracture  the  earth-crust,  or  to  pro- 
duce readjustment  of  previous  fractures,  along  their  dividing  line,  i.  e., 
along  the  margin  of  the  sea-basin.  This  is  known  to  be  the  place  of 
origin  of  most  of  the  Japanese  earthquakes.  This  would  take  place 
mainly  in  winter,  if  the  tendency  of  the  earth-forces  producing  earth- 
quakes were  to  produce  readjustment  by  subsidence  of  land  or  elevation 
of  sea-bottom. 

There  is  an  almost  universal  popular  belief  in  earthquake-regions 
that  the  occurrence  is  preceded  by  a  still,  oppressive  state  of  the  air. 
Although  no  scientific  investigations  have  confirmed  this  impression, 
yet  it  seems  quite  possible  and  even  probable  that  diminished  atmos- 
pheric pressure,  indicated  by  a  low  state  of  the  barometer,  may  act  as 
a  determining  cause  of  earthquake-occurrence,  precisely  as  the  position 
of  the  moon  on  the  meridian.  In  both  cases,  however,  we  must  regard 
these  not  as  true  causes  of  earthquakes,  but  only  as  causes  determining 
the  moment  of  occurrence. 

SECTION  4.  —  GRADUAL  ELEVATION  AND  DEPRESSION  OF  THE 
EARTH'S  CRUST. 

Of  all  the  effects  of  igneous  agencies  these  are  by  far  the  most  im- 
portant. Although  not  violent  and  destructive  like  volcanoes  and 
earthquakes,  although  indeed  so  little  conspicuous  as  to  be  generally 
unobservable  except  to  the  eye  of  science,  yet  acting  not  paroxysmally 
but  constantly,  not  in  isolated  spots  but  over  wide  areas  and  affecting 
whole  continents,  their  final  result  in  modifying  the  crust  of  the  earth 


134 


IGNEOUS   AGENCIES. 


and  making  history  is  far  greater  than  that  of  all  other  igneous  agen- 
cies put  together.  It  is  probable  that  the  same  causes  which  are  now 
at  work  gradually  raising  or  depressing  the  earth's  crust  have  during 
geological  times  formed  the  continents  and  the  seas. 

Elevation  or  Depression  during  Earthquakes.— We  have  already 
spoken  (page  105)  of  sudden  elevations  or  depressions  of  great  areas 
of  country  at  the  time  of  earthquake-occurrence  in  Hindostan,  in  the 
valley  of  the  Mississippi  River,  and  especially  of  the  southern  part  of 
South  America.  It  is  not  probable,  however,  that  much  is  accomplished 
in  this  paroxysmal  way.  These  cases  are  referred  to  in  order  to  show 
the  close  connection  of  such  sudden  bodily  movements,  and  therefore 
presumably,  also,  of  the  slower  movements  about  to  be  described,  with 
the  causes  and  forces  which  produce  earthquakes. 

Movements  not  connected  with  Earthquakes — South  America. — Be- 
sides the  sudden  elevation  of  Chili  and  Patagonia  by  earthquakes,  the 
same  countries  show  evidences  of  gradual  elevation  on  a  stupendous 
scale.  The  evidences  are  old  sea-beaches,  full  of  shells  of  species  now 
living  in  the  adjacent  sea,  far  above  the  present  water-level.  These 
"  raised  beaches  "  have  been  traced  1,180  miles  on  the  eastern  shore 
and  2,075  miles  on  the  western,  and  at  different  levels  from  100  to  1,300 
feet  above  the  sea.  More  recently  Alexander  Agassiz  has  traced  them 
by  means  of  corals  still  sticking  to  the  rocks  to  the  height  of  nearly 
3,000  feet.*  It  is  not  probable  that  all  this  movement  took  place  dur- 
ing the  present  geological  epoch,  but  it  is  the  more  instructive  on  that 
very  account,  since  it  shows  the  identity  of  geological  causes  with  causes 
now  in  operation. 

Italy. — The  most  carefully-observed  instance  of  gradual  depression 
and  elevation  is  that  of  the  coast  of  Naples.  Fig.  Ill  is  a  map  and 
Fig.  112  a  section  of  the  coast  of  the  bay  of  Baiae,  near  Naples.  Be- 


Solfatcra 


Proceedings  of  the  American  Academy  of  Sciences,  vol.  xi,  p.  287,  1876. 


ELEVATION   AND   DEPRESSION   OF   EARTH'S   CRUST.  135 

tween  a  a  a,  the  present  coast-line,  and  the  cliff  b  b  b,  which  marks 
the  position  of  the  former  coast  line,  there  is  a  nearly  level  plain 
called  the  Starza.  Now,  there  is  perfect  evidence  that  at  one  time 
the  land  was  depressed  until  the 
sea  beat  against  the  cliff  b  b,  and 
that  both  the  depression  and  the 
re-elevation  to  its  present  condition 
took  place  since  the  period  of  Ro- 
man greatness.  The  evidence  is  as 
follows:  F'°-"2- 

1.  There  are  certain  shells  abundant  in  the  Mediterranean  and  in 
many  other  seas,  called  lithodomus  (Ai0o9,  a  stone ;  domus,  a  house), 
from  the  habit  of  boring  for  themselves  holes  in  the  rocks  near  the 
water-line.  Such  borings,  often  with  the  dead  shells  in  them,  are  found 
all  along  the  base  of  the  cliff  b  b,  twenty  feet  above  the  present  sea- 
level.  2.  The  level  plain  called  Starza  is  composed  of  strata  contain- 
ing shells  of  the  Mediterranean  and  Roman  works  of  art.  3.  On  this 
plain,  near  the  present  sea-margin,  are  the  ruins  of  a  Roman  temple 
dedicated  to  Jupiter  Serapis.  The  floor  and  three  of  the  columns  d  of 
this  beautiful  work  are  still  almost  perfect  (Fig.  112).  When  first  dis- 
covered the  floor  and  the  lower  part  of  the  columns  were  covered  by 
the  materials  of  the  plain.  Above  the  part  thus  covered  the  columns 
were  bored  with  lithodomi  to  a  height  of  twenty  feet.  This  temple  was, 
of  course,  above  the  sea-level  during  the  Roman  period.  After  that 
period  it  sank  until  the  sea-level  stood  at  s'  (Fig.  112),  twenty  feet 
above  the  base.  Now,  the  floor  of  the  temple  is  again  on  a  level  with 
the  sea.  These  changes  were  so  gradual  that  they  were  entirely  insen- 
sible, and,  in  fact,  unknown  to  the  inhabitants.  The  upright  position 
of  the  columns  also  shows  that  it  could  not  have  been  produced  by 
convulsive  action.  4.  Italian  historians  state  that  in  1530  the  sea  beat 
against  the  cliff  b  b.  5.  Evidences  of  similar  changes,  in  some  cases 
depression  and  in  others  elevation,  are  seen  in  many  places  along  the 
coast  of  Italy,  Candia,  and  Greece. 

In  all  the  cases  thus  far  mentioned,  but  especially  that  of  the  tem- 
ple of  Serapis,  the  near  vicinity  of  volcanoes  (Fig.  Ill)  suggests  that 
these  effects  were  probably  in  some  way  connected  with  volcanic  ac- 
tion. But  there  are  many  instances  in  which  no  such  connection  can 
be  traced. 

Scandinavia. — The  best-observed  instance  of  this  kind  is  that  of  the 
coasts  of  Sweden.  Careful  observations  on  the  coasts  of  the  Baltic 
and  Polar  Seas  have  proved  that  nearly  the  whole  of  Norway  and 
Sweden  is  rising  slowly,  and  has  been  rising  for  thousands  of  years. 
South  of  Stockholm  there  is  no  elevation,  but,  on  the  contrary,  slight 
depression  ;  but  north  of  Stockholm  the  whole  coast  is  rising  at  a  rate 


136 


IGNEOUS  AGENCIES. 


which  increases  as  we  go  north  until  it  attains  a  maximum  of  five  to 
six  feet  per  century.  These  observations  were  made  under  the  direc- 
tion of  the  Swedish  Government  by  means  of  permanent  marks  made 
at  the  sea-level,  and  examined  from  year  to  yelr.  That  similar 
changes  have  been  in  progress  for  thousands  of  years,  Mid  have  greatly 
increased  both  the  height  and  the  extent  of  these  countries,  is  proved 
by  the  fact  that  old  sea-beaches,  full  of  shells  of  species  now  living  in 
the  neighboring  seas,  are  found  fifty  to  seventy  miles  inland,  and  100, 
200,  and  even  600  feet  above  the  present  sea-level.  In  some  places,  the 
country  rock,  when  uncovered  by  removing  superficial  deposit  of  beach- 
shells,  is  found  studded  with  barnacles  like  those  which  mark  the 
present  shore-line  (Jukes). 

The  rising  area  is  about  1,000  miles  long  north  and  south,  and  of 
unknown  breadth  It  may  embrace  a  considerable  portion  of  Russia. 
Lyell  estimates  the  average  rate  as  not  more  than  two  and  a  half  feet 
per  century.  At  this  rate,  to  rise  600  feet  would  require  24,000  years.* 
Similar  raised  beaches  are  found  in  nearly  all  countries.  We  give 
these  as  examples  of  an  almost  universal  phenomenon,  which  will  be 
again  more  perfectly  described  in  the  chapter  on  the  Quaternary. 

Greenland. — For  obvious  reasons,  evidences  of  elevation  are  much 
more  conspicuous  than  evidences  of  depression.  One  of  the  best-ob- 
served instances  of  the  latter  is  that  of  the  coast  of  Greenland.  This 
coast  is  now  sinking  along  a  space  of  600  miles.  Ancient  buildings 
on  low  rock-islands  have  been  gradually  submerged,  and  experience 
has  taught  the  native  Greenlander  never  to  build  his  hut  near  the 
water's  edge. 

Deltas  of  Large  Rivers. — In  the  deltas  of  the  Mississippi,  the 
Ganges,  the  Po,  and  many  other  large  rivers,  there  are  unmistakable 

evidences  of  gradual  depres- 
sion. These  evidences  are 
fresh- water  shells,  and  planes 
of  vegetation,  or  dirt-beds, 
far  below  the  present  level  of 
the  sea.  A  section  of  the 
delta  deposits  of  the  Missis- 
sippi River  reveals  the  fact 
that  these  deposits  consist  of 
river  sands  and  clays,  s  cl, 

FIG.  113.  (Fi£-  113)>  containing /m,-//- 

water  shells,  with  now  and 

then  an  intercalated  stratum  of  marine  origin,  I,  containing  marine 
shells,  and  at  uncertain  intervals  distinct  lines  of  turf  or  vegetable  soil, 


*  Lyell's  Antiquity  of  Man,  p.  58. 


ELEVATION  AND   DEPRESSION   OF  EARTH'S  CRUST.  137 

gl  g",  each  with  the  stumps  and  roots  of  cypress-trees  as  they  originally 
grew.  Each  one  of  these  turf -lines  is  a  submerged  forest-ground,  ex- 
cept the  uppermost,  which  is  the  present  forest-ground.  Precisely  sim- 
ilar phenomena  have  been  observed  in  other  large  deltas.  The  deltas 
of  the  Ganges  and  the  Po  have  been  penetrated  more  than  400  feet 
without  reaching  bottom.  In  both  the  deposit  is  made  up  of  fresh- water 
strata  alternating  with  dirt-beds  or  forest-grounds.  These  facts  prove 
that  these  great  deltas  have  been  at  intervals  during  the  whole  period 
of  their  formation,  as  they  are  now,  fresh-water  swamps,  overgrown  in 
parts  with  trees,  etc. ;  that  they  have  steadily  subsided  to  a  depth  indi- 
cated by  the  thickness  of  the  deposit  containing  the  old  forest-grounds  ; 
that  the  up-building  by  river-deposit  has  gone  on  pari  passu,  so  as  to 
maintain  nearly  the  same  level  all  the  time ;  but  that  from  time  to 
time  the  subsidence  was  more  rapid,  so  that  the  sea  gained  possession 
for  a  while  until  it  was  again  reclaimed  by  river-deposit,  and  again 
more  slow,  so  that  the  area  was  again  thoroughly  covered  with  forests, 
and  so  on.  These  facts  are  of  great  importance  in  geology,  and  will  be 
again  referred  to  in  the  following  pages. 

Southern  Atlantic  States. — Evidence  of  a  similar  kind  proves  that  a 
large  portion  of  the  coasts  of  our  Southern  Atlantic  States  is  slowly 
subsiding  at  the  present  time,  though  there  are  also  evidences,  in  the 
form  of  raised  beaches,  of  elevation  immediately  preceding  the  present 
subsidence.  The  evidences  of  subsidence  are  most  conspicuous  along 
the  coast  of  South  Carolina  and  Georgia.  They  consist  of  cypress- 
stumps  in  situ  below  the  present  tide-level.  According  to  Cook,  late 
Geologist  of  New  Jersey,  the  coast  from  Long  Island  to  Cape  May  is 
sinking  at  the  rate  of  two  feet  a  century. 

These  facts  seem  to  point  to  the  conclusion  that  subsidence  is  going 
on  in  nearly  all  places  where  large  deposits  of  sediment  are  accumulating. 

Pacific  Ocean. — But  by  far  the  grandest  example  of  subsidence 
known  is  that  which  has  been  going  on  for  thousands,  probably  hun- 
dreds of  thousands,  of  years,  and  is  still  going  on  in  the  mid- Pacific 
Ocean.  The  subsiding  area  is  situated  under  the  equator,  and  is  about 
6,000  miles  long  by  about  2,000  to  3,000  miles  wide.  The  evidence  of 
the  subsidence  and  its  rate  is  entirely  derived  from  the  study  of  coral- 
reefs  in  this  region.  The  further  discussion  of  the  subject  will  be  de- 
ferred until  we  take  up  coral-reefs. 

Our  examples,  be  it  observed,  are  all  taken  from  the  vicinity  of 
coast-lines,  the  sea-level  being  used  as  term  of  comparison.  In  the 
interior  of  continents,  and  in  the  midst  of  the  sea  where  there  are  no 
islands,  this  means  of  detecting  changes  fails  us,  yet  it  is  precisely 
there,  i.  e.,  in  the  middle  of  the  rising  or  subsiding  area,  that  the 
changes  are  probably  the  greatest.  In  the  case  of  continents,  however, 
as  already  explained  on  page  22,  we  have  another  test  of  crust-move- 


138  IGNEOUS  AGENCIES. 

ments,  viz.,  the  phenomena  of  river-beds.  In  a  rising  area  the  rivers 
cut  rapidly  deeper ;  in  a  subsiding  area  they  fill  up  their  old  beds  and 
rise  to  higher  level.  In  this  way  we  know  that  the  Plateau  and  the  Sierra 
regions  have  greatly  risen  in  comparatively  recent  times,  and  are  still 
rising,  while  the  New  England  region  has  recently  subsided,  though 
probably  is  not  still  subsiding.  The  evidence  of  this  will  be  given 
hereafter. 

Theories  of  Elevation  and  Depression. 

It  is  evident  that  observation  only  determines  changes  of  relative 
position  of  sea  and  land.  These  changes  may  be  the  result  of  rise  and 
fall  of  sea,  or  rise  and  fall  of  land.  The  popular  mind  naturally  at- 
tributes them  to  the  rise  and  fall  of  the  sea,  as  the  more  unstable  ele- 
ment. But,  by  the  principle  of  hydrostatic  level,  it  is  clearly  impos- 
sible that  the  ocean  should  rise  or  fall  permanently  at  one  place  without 
being  similarly  affected  everywhere.  It  is  certain,  therefore,  that  the 
changes  we  have  described  above,  being  in  different  directions  in  dif- 
ferent places,  must  be  due  to  movements  of  the  solid  crust.  Neverthe- 
less, it  is  also  true  that  any  increase  in  the  height  and  extent  of  the 
whole  amount  of  land  on  the  globe  must  be  attended  with  a  correspond- 
ing depression  of  the  sea-bottoms,  and  therefore  an  actual  subsidence 
of  the  sea-level  everywhere.  Hence,  if  it  be  true,  as  is  generally  be- 
lieved, that  the  continents  have  been,  on  the  whole,  increasing  in  ex- 
tent and  in  height,  in  the  course  of  geological  history,  then  it  is  true 
also  that  the  seas  have  been  subsiding,  and  that  therefore  the  relative 
changes  are  the  sum  of  these  two. 

Admitting,  however,  that  the  actual  increase  of  land  at  the  present 
time  is  imperceptible,  or  at  least  very  small  in  comparison  with  the 
oscillatory  movements  described  above,  we  may  look  upon  the  sea-level 
as  fixed;  this  statement  being  sufficiently  correct  when  regarding  the 
subject  from  the  physical  point  of  view,  though  untenable  when  re- 
garded from  the  geological  point  of  view.  Admitting,  then,  the  fixed- 
ness of  the  sea-level,  what  are  the  causes  of  the  gradual  movements  of 
the  solid  crust  ? 

Babbage's  Theory. — Babbage  believed  that,  in  the  vicinity  of  volca- 
noes, the  rise  and  fall  of  ground  were  due  to  the  expansion  and  con- 
traction of  rocks  by  heating  and  cooling.  The  re-elevation  of  the 
temple  of  Serapis  occurred  apparently  soon  after  the  eruption  which 
formed  Monte  Nuovo  (Fig  111).  It  is  not  improbable  that  this  re- 
elevation  was  the  result  of  the  heating  and  vertical  expansion  of  the 
rocks  to  great  depth,  caused  by  the  eruption  of  the  interior  heat  at 
this  point.  A  very  small  elevation  of  temperature  of  rocks  several 
miles  thick  would  be  sufficient  to  produce  a  vertical  expansion  of 
twenty  feet. 

Other  cases,  such  as  the  rise  of  sea-margins  at  a  distance  from 


THEORIES   OF  ELEVATION  AND   DEPRESSION.  139 

volcanic  action,  Babbage  explains  as  follows :  Large  accumulations 
of  sediments,  such  as  occur  generally  on  coasts,  would  cause  a  rise 
toward  the  surface  of  all  the  subjacent  isogeotherms.  This  increase  of 
temperature  of  the  crust  would  cause  a  vertical  expansion  or  swelling 
of  the  crust  at  that  point,  and  a  consequent  rise  above  the  sea-level. 

The  great  objections  to  this  theory,  as  applied  to  these  latter  cases, 
are :  1.  The  elevation  of  sea-bottom  from  this  cause  would  not  affect 
the  contiguous  land;  and,  2.  That  the  places  where  the  greatest 
quantities  of  sediments  are  depositing  (as,  for  instance,  the  deltas  of 
great  rivers)  are  places  of  subsidence,  instead  of  elevation. 

Herschel's  Theory.* — Sir  John  Herschel  assumes,  as  a  general  law 
—what  has  been  proved  in  a  great  number  of  instances — that  areas 
of  great  accumulation  of  sediment  are  areas  of  subsidence.  He  agrees 
with  Babbage,  that  accumulation  of  sediments  must  cause  an  upward 
movement  of  the  isogeotherms,  but  he  differs  from  Babbage  in  believ- 
ing that  this  invasion  of  sediments  by  the  interior  heat  would  produce 
subsidence  instead  of  elevation.  For,  according  to  Herschel,  the  inva- 
sion of  sediments  by  the  interior  heat  would  produce  chemical  changes, 
and  sometimes  even  aqueo-igneous  fusion.  These  chemical  changes, 
whatever  other  effects  they  produce,  would  certainly  change  loose  sedi- 
ments into  denser  crystalline  rocks  (metamorphism),  thus  producing 
contraction  instead  of  expansion.  The  accumulating  sediment  mean- 
while would  subside,  by  the  pressure  of  its  own  weight,  on  the  liquid 
or  semi-liquid  thus  formed. 

Recent  View. — Again :  On  the  view  that  there  exists  a  sub-crust 
layer  of  liquid  matter  (page  87),  not  only  would  loading  with  sedi- 
ment cause  subsidence  of  marginal  sea-bottoms,  but  also  lightening  by 
erpsion  would  produce  elevation  of  land- surf  aces. 

General  Theory. — The  theory  of  Babbage  accounts  with  great  prob- 
ability for  the  rise  of  ground  in  the  vicinity  of  volcanoes,  and  Ilerschel's 
theory  accounts,  perhaps,  for  the  subsidence  of  deltas  and  other  places 
where  great  accumulation  of  sediments  occurs ;  and  this  latter  theory 
has  the  additional  advantage  of  accounting  for  metamorphism,  and 
perhaps,  also,  for  volcanic  phenomena.  But  it  is  evident  that  some 
other  and  more  general  theory  is  necessary  to  account  for  those  great 
inequalities  of  the  earth's  crust  which  form  land  and  sea-bottom.  For 
example  :  although  loading  with  sediment  may  cause  sea-bottoms  to 
sink ;  and  lightening  by  erosion  may  cause  land-surfaces  to  rise,  yet 
this  does  not  at  all  explain  how  sea-bottoms  and  land-surfaces  came  to 
be  such.  These  great  inequalities  must  be  originated  by  some  other 
cause  ;  loading  and  lightening  only  tend  to  maintain  them.  The  for- 

*  Herschel,  Proceedings  of  the  Geological  Society,  vol.  ii,  p.  548 ;  and  Babbage,  ibid., 
p.  72. 


140  ORGANIC  AGENCIES. 

mation  of  these  must  be  a  phenomenon  somewhat  different  from  those 
local  oscillations  which  alone  have  been  the  subject  of  direct  observa- 
tion. Such  general  changes  can  only  be  the  result  of  gradual  unequal 
contraction  of  the  whole  earth  consequent  upon  its  secular  cooling. 
The  further  discussion  of  this  theory,  however,  belongs  properly  to  the 
second  part  of  this  work. 


CHAPTER  IV. 
ORGANIC  AGENCIES. 

As  agents  modifying  the  crust  of  the  earth,  organisms  are,  per- 
haps, inferior  to  the  agents  already  mentioned  (although  the  immense 
thickness  and  extent  of  limestone  strata  are  a  monument  of  their  power 
in  this  respect) ;  nevertheless,  they  are  peculiarly  interesting  to  the 
geologist  as  delicate  indicators  of  climate,  and  recorders  of  the  events 
of  the  earth's  history.  We  will  take  up  the  subject  of  their  agency 
under  three  heads,  each  having  a  separate  application  in  interpreting 
the  structure  and  history  of  the  earth,  viz. :  1.  Vegetable  Accumula- 
tions, to  account  for  coal  and  bitumen ;  2.  Bog- Iron  Ore,  to  account 
for  iron-ores  inclosed  in  the  strata ;  3.  Lime  Accumulations,  to  account 
for  limestones,  etc. 

SECTION  1. — VEGETABLE  ACCUMULATIONS. 
Peat-Bogs  and  Peat-Swamps. 

Description. — In  humid  climates,  in  certain  places,  badly  drained 
and  overgrown  with  moss  and  shrubs,  a  black  carbonaceous  mud  accu- 
mulates often  to  great  depths.  This  substance  is  called  peat  or  turf, 
and  such  localities  peat-bogs.  The  thick  mass  of  vegetation  which 
covers  their  surface,  with  its  interlaced  roots  often  forms  a  crust  upon 
which  a  precarious  footing  may  be  found,  but  beneath  this  is  a  tremu- 
lous, semi-fluid  quagmire,  sometimes  twenty  to  forty  feet  deep,  in 
which  men  and  animals,  venturing  in  search  of  food,  are  often  lost. 
These  bogs  are  most  numerous  in  northern  climates.  One  tenth  of  the 
whole  surface  of  Ireland,  and  large  portions  of  Scotland,  England,  and 
France,  are  covered  with  peat.  The  bog  of  the  Shannon  River  is  fifty 
miles  long  and  three  miles  wide ;  that  of  the  Loire  in  France  is  150 
miles  in  circumference.  Extensive  bogs  exist  also  in  the  northern  por- 
tions of  our  own  country.  The  amount  of  peat  in  Massachusetts  alone 
has  been  estimated  at  more  than  15,000,000,000  cubic  feet  (Dana).  In 
California,  an  imperfect  peat  covers  large  areas  about  the  mouth  of  the 
San  Joaquin  River  and  elsewhere  (tule-lands).  In  more  southern  cli- 


PEAT-BOGS  AND  PEAT-SWAMPS.  141 

mates,  where  the  condition  of  humidity  is  present,  immense  accumula- 
tions of  peat  also  occur — not,  however,  in  bogs  overgrown  with  moss 
and  shrubs,  but  in  extensive  swamps  covered  with  large  trees. 

Composition  and  Properties  of  Peat. — Peat  is  disintegrated  and 
partially  decomposed  vegetable  matter.  It  is  composed  of  carbon,  with 
small  and  variable  quantities  of  hydrogen,  oxygen,  and  nitrogen.  It  is, 
therefore,  vegetable  matter  which  has  lost  a  part  of  its  gaseous  con- 
stituents, and  in  which,  therefore,  the  carbon  is  greatly  in  excess.  In 
more  recent  peat,  the  vegetable  nature  and  structure  are  plainly  detect- 
able by  the  eye,  but  in  older  peat  only  by  the  microscope.  In  all  coun- 
tries where  it  occurs,  it  is  dried  and  used  as  a  valuable  domestic  fuel. 
By  powerful  pressure  it  may  be  converted  into  a  substance  scarcely 
distinguishable  from  some  varieties  of  coal,  and,  thus  changed,  is  now 
extensively  used  for  all  purposes  for  which  coal  is  used,  and  has  there- 
fore become  an  important  article  of  commerce. 

Peat  possesses  a  remarkable  antiseptic  property.  This  property  is 
probably  due  to  the  presence  of  humic  acid  and  of  hydrocarbons  anal- 
ogous to  bitumen,  which  are  formed  only  when  vegetable  matter  is 
decomposed  in  presence  of  excess  of  water.  The  bodies  of  men  and 
animals  have  been  found  in  bogs  in  a  good  state  of  preservation,  which 
must  have  been  buried  many  hundred  years.  In  1747,  in  an  English 
bog,  the  body  of  a  woman  was  found,  with  skin,  nails,  and  hair,  almost 
perfect,  and  with  sandals  on  her  feet.  In  Ireland,  under  eleven  feet  of 
peat,  the  body  of  a  man  was  found  clothed  in  coarse  hair-cloth.  Several 
other  instances  of  bodies  of  men  and  animals,  and  innumerable  in- 
stances of  skeletons  of  animals,  preserved  in  bogs  where  they  have  per- 
ished, might  be  mentioned.  Large  trunks  of  trees  are  often  so  per- 
fectly preserved  that  they  are  used  as  timber,  and  stumps  similarly 
preserved  are  found  with  their  roots  firmly  fixed  in  the  under-soil  of 
the  bog  as  if  they  had  grown  on  the  original  soil  on  which  the  bog  was 
accumulated. 

Mode  of  Growth. — Plants  take  the  greater  portion  of  their  food  from 
the  air,  and  give  it,  by  the  annual  fall  of  leaf  and  finally  by  their  own 
death,  to  the  soil.  Thus  is  formed  the  humus  or  vegetable  mold  found 
in  all  forests.  This  substance  would  increase  without  limit  were  it  not 
that  its  decay  goes  on  pari  passu  with  its  formation.  But  in  peat-bogs 
and  swamps  the  excess  of  water,  and,  still  more,  the  antiseptic  property 
of  the  peat  itself,  prevent  complete  decay.  Thus  each  generation  takes 
from  the  air  and  adds  to  the  soil  continually  and  without  limit.  The 
soil  which  is  made  up  entirely  of  this  ancestral  accumulation  continues 
to  rise  higher  and  higher,  until  the  bog  often  becomes  higher  than  the 
surrounding  country,  and,  when  swollen  by  unusual  rains,  bursts  and 
floods  the  country  with  black  mud.  A  bog  is  therefore  composed  of 
the  vegetable  matter  of  thousands  of  generations  of  plants.  It  repre- 


142  ORGANIC  AGENCIES. 

serits  so  much  matter  withdrawn  from  the  atmosphere  and  added  to 
the  soil.  In  some  cases,  besides  the  material  deposited  from  the 
growth  of  vegetation  in  situ,  the  accumulation  may  be  partly  also  the 
result  of  organic  matter  drifted  from  the  surrounding  surface-soil. 

Rate  of  Growth. — The  rate  of  peat-growth  must  be  very  variable, 
since  it  depends  upon  the  vigor  of  the  vegetation  and  upon  the  manner 
of  accumulation,  whether  entirely  by  growth  of  plants  in  situ,  or  partly 
by  driftage.  Many  of  the  European  bogs  are  evidently  the  growth  of 
not  more  than  eighteen  hundred  years,  for  they  were  forests  in  the 
time  of  the  Romans,  or  even  later.  The  felling  of  these  forests,  as  a 
military  measure  to  complete  the  subjugation  of  the  country,  and  the 
consequent  impediments  to  drainage  thus  produced,  have  changed 
them  into  bogs.  At  their  bottoms,  and  covered  with  eight  to  ten  feet 
of  peat,  are  found  the  trunks  and  the  stumps  of  the  original  .forests, 
the  axes  and  coins  of  the  Roman  soldiers,  and  the  roads  of  the  Roman 
army.  The  rate  of  accumulation  has  been  variously  estimated,  from 
one  or  two  inches  to  several  feet  per  century.  In  all  cases  of  simple 
growth  in  situ,  however,  and  therefore  always  in  great  peat-swamps, 
the  increase  is  very  slow. 

Conditions  of  Growth. — The  conditions  usually  considered  necessary 
for  the  formation  of  peat  are  cold  and  moisture;  and  of  these  the 
former  is  considered  the  more  important,  as  without  cold  it  is  supposed 
vegetable  matter  would  be  destroyed  by  decay.  In  proof  of  this  it  is 
stated  that  peat-bogs  are  more  numerous  in  cold  climates.  But  it  is 
more  probable  that  excess  of  moisture  is  the  only  important  condition. 
This  condition  may  be  rarer  in  warm  climates  on  account  of  the  greater 
capacity  of  the  air  for  moisture  in  these  climates ;  but  when  it  is  pres- 
ent, immense  accumulations  of  peat  occur  in  extensive  swamps.  The 
Great  Dismal  Sivamp  is  a  good  illustration.  This  swamp,  situated 
partly  in  North  Carolina  and  partly  in  Virginia,  is  forty  miles  long  by 
twenty-five  miles  wide.  It  is  covered  with  a  dense  forest  of  cypress 
and  other  swamp  trees,  by  the  annual  fall  of  whose  leaves  the  peat  is 
formed.  These  trees,  by  means  of  their  long  tap-roots  and  their  wide- 
spreading  lateral  roots,  maintain  a  footing  in  the  insecure  soil,  but  are 
often  overthrown,  and  add  their  trunks  and  branches  to  the  vegetable 
accumulation.  The  original  soil,  upon  which  the  accumulation  was 
formed,  must  have  been  lower  in  the  center,  but  the  surface  of  the  peat 
rises  very  gently  toward  the  center,  which  is  twelve  feet  higher  than 
the  circumference  (Fig.  114).  Near  the  center  there  is  a  lake  of  clear, 
wine-colored  water,  seven  miles  across  and  fifteen  feet  deep,  the  banks 
and  bottom  of  which  are  composed  of  pure  peat. 

In  the  Mississippi  River  swamps  there  are  also  large  areas  where  pure 
peat  has  been  accumulating  for  ages,  and  is  still  accumulating,  by 
growth  of  trees  in  situ,  though  subject  to  the  annual  floods  of  the  river. 


BOG-IRON  ORE.  143 

The  pureness  of  the  peat  in  these  cases  is  due  to  the  fact  that  the  mud- 
dy waters  of  the  river  are  strained  of  all  their  sedimentary  matter  by 


FIG.  114.— Ideal  section  through  Dismal  Swamp,    a  a,  original  soil ;  b  b,  peat ;  I,  lake. 

passing  through  the  dense  jungle-growth  of  cane  and  herbage  which 
surrounds  these  favored  spots.  Thus  only  pure  water  reaches  them.* 
Similar  peat-swamps  are  found  at  the  mouths  of  the  Ganges,  the  Kiger, 
and  other  great  rivers. 

Alternation  of  Peat  with  Sediments. — We  have  already  stated  (page 
13G)  that  a  section  of  the  delta-deposit  of  many  great  rivers,  such  as  the 
Mississippi,  Ganges,  and  Po,  reveals  alternate  layers  of  fresh-water  and 
marine  sediments,  with  thin  layers  of  vegetable  mold  containing 
stumps.  In  some  cases  these  layers  of  vegetable  mold  amount  to  con- 
siderable thickness  of  turf  or  peat.  Layers  of  peat  two  feet  thick  have 
been  found  between  layers  of  river-mud  in  the  delta  of  the  Ganges 
(Lyell's  Principles  of  Geology).  Similar  layers  have  been  found  in 
the  delta  of  the  Po.  They  are  evidently  submerged  peat-swamp*. 
These  facts  are  of  great  importance  in  the  explanation  of  the  accumu- 
lation of  coal. 

Drift- Timber. 

Great  rivers  in  wooded  countries  always  bring  down  in  large  num- 
bers the  trunks  of  trees  torn  from  the  soil  of  their  banks.  These  trunks 
lodging  near  their  mouths,  where  the  current  is  less  swift,  and  accumu- 
lating from  year  to  year,  form  rafts  of  great  extent.  The  great  raft 
of  the  Atchafalaya,  which  was  removed  in  1835  by  fhe  State  of 
Louisiana,  was  a  mass  of  timber  ten  miles  long,  seven  hundred  feet 
wide,  and  eight  feet  thick.  It  had  been  accumulating  for  more  than 
fifty  years,  and  at  the  time  of  its  removal  was  covered  with  vegetation, 
and  even  with  trees  sixty  feet  high.  Similar  accumulations  of  drift- 
wood are  described  as  occurring  in  the  Bed  River,  the  Mackenzie 
River,  and  in  Slave  Lake.  Such  rafts  become  finally  imbedded  in 
river-mud,  and  undergo  a  slow  change  into  lignite  or  imperfect  coal. 
Beds  of  partially- formed  lignite  are  therefore  found  in  sections  of  the 
delta-deposit  of  almost  all  great  rivers.  We  will  use  these  facts  in 
speaking  of  the  theories  of  the  coal. 

SECTION  2. — BOG-IRON  ORE. 

At  the  bottom  of  peat-bogs  is  often  found  a  "  hard  pan  "  of  iron- 
ore,  sometimes  one  to  two  feet  thick.  The  same  material  often  collects 
in  low  spots,  even  when  there  is  no  decided  bog.  The  manner  in  which 

*  Lyell's  Elements  of  Geology,  fifth  edition,  p.  885. 


144  ORGANIC  AGENCIES. 

this  iron-ore  accumulates  is  very  interesting,  and  in  a  geological  point 
of  view  very  important. 

Peroxide  of  iron  exists  very  generally  diffused  as  the  red  coloring- 
matter  of  soils  and  rocks.  In  this  form,  however,  it  is  insoluble,  and 
therefore  can  not  be  washed  out  by  percolating  waters.  For  this  pur- 
pose the  agency  of  decomposing  organic  matter,  present  in  all  percolat- 
ing waters,  is  necessary.  Decomposition  of  organic  matter  is  a  process 
of  oxidation.  In  contact  with  peroxide  of  iron  (ferric  oxide)  it  deoxi- 
dizes, and  reduces  it  to  protoxide  (ferrous  oxide).  The  acids,  especially 
carbonic  acid,  produced  by  decomposition  of  the  organic  matter,  then 
unite  with  the  protoxide,  forming  carbonate  of  iron.  The  carbonate, 
being  soluble  in  water  containing  excess  of  carbonic  acid,  is  washed 
out,  leaving  the  soils  or  rocks  decolorized,  and  the  iron-charged  waters 
come  up  as  chalybeate  springs.  But  the  ferrous  carbonate  rapidly 
oxidizes  again  in  the  presence  of  air,  by  exchanging  its  carbonic  acid 
for  oxygen,  and  returns  to  its  former  condition  of  ferric  oxide,  and  is 
deposited.  Thus  all  about  iron-springs,  and  in  the  course  of  the 
streams  which  flow  from  them,  and  in  low  places  where  their  waters 
accumulate,  we  find  reddish  deposits  of  hydrated  ferric  oxide.  This 
is  the  most  common  but  not  the  only  form.  For  if  the  iron- waters 
accumulate,  and  the  iron  be  deposited  in  the  presence  of  excess  of 
organic  matter,  as  peat,  then  the  iron  is  not  (for  in  the  presence  of 
this  reducing  agent  it  can  not  be)  reoxidized,  but  remains  in  the  form 
of  ferrous  carbonate. ' 

Thus  there  are  two  forms  in  which  iron  leached  out  from  the  soils 
and  rocks  may  accumulate,  viz.,  ferric  oxide  and  ferrous  carbonate  :  the 
former  is  accumulated  where  the  organic  matter  is  in  small  quantities, 
and  consumes  itself  in  doing  the  work  of  dissolving  and  carrying ;  the 
latter  where  the  organic  matter  is  in  excess. 

Many  familiar  phenomena  may  be  explained  by  the  principles  given 
above  :  1.  Clay  containing  both  iron  and  organic  matter  is  never  red, 
but  always  blue  or  slate-colored,  because  the  iron  is  in  the  form  of  fer- 
rous carbonate ;  but  the  same  clay  will  make  good  red  brick,  because 
by  burning  the  organic  matter  is  destroyed  and  the  iron  peroxidized. 
2.  In  red-clay  soils,  such  as  those  of  our  primary  regions,  the  surface- 
soil,  especially  in  forests,  is  always  decolorized,  the  coloring  of  peroxide 
of  iron  being  washed  oat  and  carried  deeper  by  water  containing  or- 
ganic matter  derived  from  the  vegetable  mold.  3.  In  sections  of  red 
clay,  at  the  sides  of  gullies  or  railroad-cuttings,  along  every  fissure  or 
crevice  through  which  superficial  waters  percolate,  the  clay  is  bleached. 
The  marbled  appearance  of  red  clays  is  also  probably  due,  in  a  great 
measure,  to  the  irregular  percolation  of  superficial  waters  containing 
organic  matter.  4.  The  under  clay  or  sand  of  peat-bogs  is  usually 
decolorized. 


CORAL   REEFS  AND   ISLANDS.  145 

We  will  hereafter  make  use  of  these  facts  and  principles  in  the  ex- 
planation of  beds  of  iron-ore. 

SECTION  3. — LIME  ACCUMULATIONS. 
Coral  Reefs  and  Islands. 

Interest  and  Importance. — The  subject  of  corals  and  coral  reefs  is 
one  of  much  popular  as  well  as  scientific  interest.  The  strange  forms 
and  often  splendid  colors  of  the  living  animals ;  the  number  and  ex- 
treme beauty  of  the  coral  islands  which  gem  the  surface  of  certain 
seas ;  the  large  amount  of  habitable  land  which  owes  its  existence  to 
the  agency  of  these  minute  animals  ;  the  fact  that  a  large  area,  prob- 
ably several  thousand  square  miles,  has  been  thus  added  to  our  own 
territory ;  the  great  dangers  connected  with  the  navigation  of  coral 
seas,  strikingly  displayed  on  our  own  coast  by  the  fact  that  the  consid- 
erable town  of  Key  West  is  almost  wholly  dependent  on  the  wrecking 
business  for  its  existence — these  and  many  other  facts  invest  the  sub- 
ject with  popular  interest,  while  the  great  importance  of  corals  as  a 
geological  agent  gives  the  subject  a  scientific  interest  no  less  strong. 

Coral  Polyp. — The  animal  which  secretes  coralline  stone  is  no  insect, 
as  generally  supposed,  but  belongs  to  one  of  the  lowest  divisions  of  the 
animal  kingdom,  viz.,  the  class  of  polyps.  Like  most  of  the  lowest 
animals,  it  is  composed  of  soft,  gelatinous,  and  almost  transparent 
tissue.  The  animal,  however,  has  the  power  of  extracting  carbonate  of 
lime  from  sea-water,  and  depositing  it  within  its  own  body.  The  lime 
carbonate  is  deposited  only  in  the  lower  portion  of  the  animal,  leaving 
thus  the  upper  part  and  the  tentacles  free  to  move.  The  radiated 
structure  of  the  polyp  is  pefectly  reproduced  in  the  coralline  axis. 
This  is  a  purely  vital  function,  having  no  more  connection  with  voli- 
tion than  the  secretion  of  the  shell  of  an  oyster  or  the  bones  of  the 
higher  animals.  The  limestone  thus  deposited  within  the  animal  con- 
stitutes 90  to  95  per  cent  of  its  whele  weight. 

Compound  Coral,  or  Corallum. — A  single  coral  polyp  is  very  small, 
but,  like  many  of  the  lower  animals,  it  has  the  power  of  multiplying 
indefinitely  by  buds  and  branches.  Thus  are  formed  compound  corals. 
These  may  branch  profusely,  and  then  may  be  called  coral-trees  ;  or 
may  grow  in  hemispherical  masses,  and  are  then  called  coral-heads. 
Coral-trees  are  sometimes  six  or  eight  feet  high,  and  coral-heads  fifteen 
to  twenty  feet  in  diameter.  They  consist  of  millions  of  individual 
coral  polyps.  Only  the  upper  and  outer  portions  of  a  coral- tree,  and 
outer  portion  of  a  coral-head,  are  living ;  the  lower  and  interior  por- 
tions consist  only  of  coralline  limestone  without  life. 

Coral  Forests. — Coral  polyps,  however,  reproduce  not  only  by  bud- 
ding, but  also  by  eggs.  These  eggs  have  the  power  of  locomotion. 

10 


146  ORGANIC   AGENCIES. 

As  soon  as  they  are  extruded,  they  swim  and  float  away,  and,  if  they 
fall  on  sea-bottom  favorable  for  their  growth,  they  soon  form  first  a 
coral  polyp,  and  finally  a  coral-tree  or  coral-head.  Thus  from  one 
coral-tree  other  coral-trees  spring  up  all  around  and  form  a  coral  for- 
est, which  spreads  in  every  direction  where  they  find  conditions  favor- 
able. 

Coral  Reef, — Finally,  the  limestone  accumulation  of  thousands  of 
successive  generations  of  coral  forests  growing  and  dying  on  the  same 
spot,  together  with  the  shells  of  mollusks  and  the  bones  of  fishes  which 
live  in  swarms  preying  on  the  corals,  the  whole,  of  course,  crowned  with 
the  living  forest  of  the  present  generation,  constitute  the  coral  reef.  It 
is  evident,  then,  that  a  reef  is  formed  somewhat  after  the  manner  of  a 
peat-bog.  As  a  peat-bog  represents  so  much  matter  taken  from  the  air, 
so  a  coral  reef  represents  so  much  matter  taken  from  the  sea-water. 
As  each  generation  adds  itself  to  the  ancestral  funeral-pile,  the  ground 
upon  which  the  corals  grow  steadily  rises  until  it  becomes  elevated  far 
above  the  surrounding  sea-bottom. 

Coral  Islands. — These  are  due  to  the  action  of  waves  upon  the  coral 
reefs.  We  have  already  seen  how  low  islands  are  formed  on  submarine 

banks  by  this  agency. 
Now,  reefs  are  also  a 
kind  of  submarine 
bank.  On  these,  there- 

FIG.  115.  . 

fore,   islands    are    also 

formed  by  waves.  Fig.  115  represents  an  ideal  section  across  a  reef,  as 
it  would  be  if  no  wave-action  interfered,  1 1  being  the  sea-level.  But  by 
the  action  of  the  beating  waves  during  storms  large  masses  of  reef- 
rock,  often  six  or  eight 
feet  in  diameter,  or  great 
coral-heads,  are  broken 

^?<  ^^^.  off  from  the  outer  or 

S*^  seaward  side  of  the  reef 

j  and  rolled  over  to  the 

leeward    side.       These 

form  a  nucleus  about  which  collect  similar  or  smaller  fragments,  and 
among  these  still  smaller  fragments,  and  these  again  are  filled  in  and 
made  firm  with  coral-sand,  and  the  whole  cemented  into  solid  limestone 
rock  (breccia)  by  the  carbonate  of  lime  in  the  sea- water. 

Islands  thus  formed,  like  all  wave-formed  islands,  are  low  (twelve 
to  fifteen  feet  high)  and  narrow  (one  quarter  to  one  half  mile  wide), 
but  long  in  the  direction  of  the  reef.  They  are  at  first  perfectly  bare, 
but  become  in  time  covered  with  vegetation,  and  even  teeming  with 
population.  They  are  celebrated  for  their  gem-like  beauty.  '  The  final 
result  is  shown  in  ideal  section  in  Fig.  116,  in  which  the  dotted  portion 


CORAL   REEFS  AND   ISLANDS.  147 

is  reef -rock,  the  strong  waving  line  the  surface  of  the  living  reef,  and 
the  shaded  portion  the  island. 

Conditions  of  Coral-Growth. — Reef-building  corals  do  not  grow  in 
all  seas,  nor  over  the  whole  bottom  of  the  sea  indiscriminately,  but  are 
confined  to  certain  seas,  and  in  these  to  certain  spots  and  lines.  The 
conditions  of  the  growth  are  : 

1.  A  Winter  Temperature  of  68°. — This  condition  confines  them  al- 
most entirely  to  the  torrid  zone.     The  most  marked  exception  to  this 
is  on  the  Florida  coast  and  the  Bahamas,  where  corals  extend  to  28° 
north  latitude,  and  in  the  Bermudas  to  32°  north  latitude.     This  exten- 
sion of  the  usual  limits  of  reef-building  corals  is  due  to  the  warm  tropi- 
cal waters  carried  northward  by  the  Gulf  Stream. 

2.  A  Depth  of  not  more  than  One  Hundred  Feet. — This  condition 
confines  them  to  submarine  banks,  and  especially  to  the  shores  of  con- 
tinents and  islands. 

3.  Clearness  and  Saltness  of  the  Water. — On  account  of  this  condi- 
tion corals  will  not  grow  on  muddy  shores,  nor  off  the  mouths  of  rivers, 
being  destroyed  by  the  fresh  and  muddy  water. 

4.  Free  Exposure  to  Waves. — Some  species  of  corals  grow  in  still 
water,  but  the  strongest  reef-building  species  delight  in  the  dash  of  the 
surf.     They  will  even  flourish  and  build  an  almost  perpendicular  wall 
in  breakers  which  would  wear  away  the  hardest  rock.     The  reason  is, 
that  the  immense  profusion  of  life  on  a  reef  rapidly  exhausts  the  water 
of  the  oxygen  necessary  for  respiration,  and  of  the  carbonate  of  lime 
necessary  for  their  stony  structure,  and  therefore  constant  change  of 
water  is  necessary. 

All  the  conditions  mentioned  above  apply  only  to  reef-building 
species.  Some  corals  live  in  temperate  regions,  some  in  very  deep 
water,  and  some  in  sheltered  places. 

Pacific  Reefs, — The  reefs  of  the  Pacific  Ocean  are  of  three  general 
kinds,  viz.,  fringing  reefs,  barrier  reefs,  and  circular  reefs  or  atolls. 
We  will  describe  these  in  the  order  mentioned. 

Fringing  Reefs. — In  the  tropical  Pacific  every  high  island  or  previ- 
ously-existing land  of  any  kind  is  surrounded  by  a  reef  which  attaches 
itself  to  the  shore-line,  and  extends  outward  on  every  side  just  beneath 
the  water-level,  as  far  as 
the  condition  of  depth 
will  allow,  thus  forming 
a  submarine  platform 
bordering  the  island  or 
other  land.  At  the  outer 
margin  of  this  platform 

the  bottom  drops  off  very  suddenly,  forming  a  slope  of  50°  to  60°,  and 
sometimes  almost  perpendicularly.      The  position  and  extent  of  the 


148 


ORGANIC  AGENCIES. 


coral  platform  is  indicated  to  the  eye  of  the  observer  by  a  white  sheet 
of  breakers  which  surrounds  the  island  like  a  snowy  girdle,  and  ex- 
tends some  distance  from  the  shore-line  (Fig.  117).  The  section  Fig. 
118  will  give  a  clear  idea  of  the  contour  of  land  and  sea  bottom.  In 

this  and  the  fol- 
lowing sections 
the  dotted  parts 
represent  coral 


PIG.  118.  formation.      If 

j  the    island      is 

large,  and  considerable  rivers  flow  into  the  sea,  breaks  in  the  reef  plat- 
form will  occur  opposite  the  mouths  of  the  rivers,  the  corals  in  these 
places  being  destroyed  by  the  fresh,  muddy  waters.  In  the  case  of 
fringing  reefs  no  islands  are  formed  by  the  action  of  waves,  but  only  a 
shore-addition  to  the  original  island,  as  shown  at  a  a  in  the  section. 

Barrier  Reefs. — In  many  cases  besides  the  fringing  reef  there  is 
another  reef  surrounding  the  island  like  a  submarine  rampart  at  the  dis- 
tance of  from  ten  to  fifty  miles.  As  the  reef  rises  nearly  to  the  surface 
of  the  sea,  its  position  is  indicated  by  a  snowy  girdle  of  breakers  sur- 
rounding the  island 
at  a  distance,  and 
this  snowy  girdle  is 
gemmed  with  wave- 
formed  green  islets. 
Within  this  girdle, 
and  between  the 
rampart  and  the 
island,  there  is  a  ship-channel  twenty  or  thirty  fathoms  deep  (Fig.  119). 
Through  breaks  in  the  coral  rampart  ships  enter  this  channel  and  find 
A  ^  secure  harbor  in  a 

ti 


stormy    sea.      The 
section  Fig.  120  will 
give  a  clear  idea  of 
FIG.  120.  the     conformation 

of  bottom.     On  the  landward  side  of  the  coral  rampart  the  slope  of 

the  bottom  is  gentle,  but  on  the  seaward  side  it  is  very  steep,  so  that 

it  is  almost  unfathomable  at  a  short  distance  from  the  reef. 
Circular  Reefs,  or 

Atolls. — These  are  the 

most  wonderful  of  the 

reefs    of    the    Pacific. 

In  a  circular  reef  there 

is  no  volcanic  island  or 

other  visible    land    to  FIG.  121. 


FIG.  119. 


CORAL   REEFS  AND   ISLANDS. 


149 


which  the  reef  is  attached.  Imagine  a  circular  line  of  breakers  like  a 
snow-wreath  on  the  sea,  indicating  a  circular  submarine  ridge  (the  cor- 
al reef)  gemmed 

as     before      with       ^tf ^ 

wave-formed  isl- 
and within 
circle  a  la- 


FlG 122> 


ets  : 

the 

goon    of     placid 

water    twenty   or 

thirty       fathoms 

deep  (Fig.  121).     It  is  a  submarine  urn  standing   in   unfathomable 

water,  as  seen  in  the  section  Fig.  122.  Through  breaks  in  the  reef 

ships  enter  the 
charmed  circle 
and  find  safe 
harbor.  By 

means  of  sound- 
ing it  is  found 

p^^^8^*?^^^^-  ^llBpfc  that  on  the  in- 
'S&sZSg^^&fjiBg^  tcrior  or  lagoon 

side  the  slope  of 
the  bottom  is 
very  gentle,  but 
on  the  outer  or 
seaward  side  is 

FIG.  123.-View  of  Whitsunday  Island.  y          steep,  often 

50°  to  60°,  and  sometimes  in  places  almost  perpendicular  to  very 
great  depth.  Fig.  123  gives  a  perspective  view,  and  Fig.  124,  a, 
a  map  view,  of  an  atoll, 
showing  the  irregular  cir- 
cular form  of  the  reef  and 
the  little  islands  which  gem 
its  surface. 

Small  Atolls  and  La- 
goonless  Islands. — Besides 
the  atolls  already  described, 
there  are  others,  evidently 
of  similar  origin,  but  much 
smaller,  in  which  the  land 
is  continuous.  Sometimes 

the  continuous  line  is  open  FlG  124 

on  one  side  (Fig.  124,  #), 

and  the  lagoon  is  still  in  connection   with  the  open  sea.      Sometimes 
the  circle  of  land  is  complete,  and  the  lagoon  is  isolated  from  the  sea 


150  ORGANIC  AGEXCIES. 

(Fig.  124,  c).  Sometimes  the  lagoon  closes  up,  and  a  lagoonless  island 
is  the  result  (Fig.  124,  d).  These  different  forms  graduate  into  one 
another  and  into  the  typical  atoll. 

Theories  of  Barrier  and  Circular  Reefs. 

Fringing  reefs  require  no  theory.  Corals  attach  themselves  to  the 
shore-line  because  they  find  there  the  depth  necessary  for  their  growth, 
and  they  extend  outward  until  they  are  limited  by  the  increasing  depth. 
But  there  is  a  real  difficulty  in  explaining  barriers,  for  they  seem  to  rise 
from  water  too  deep  for  coral-growth  ;  and  the  difficulty  becomes  still 
greater  in  the  case  of  circular  reefs  or  atolls,  for  these  seem  to  have  no 
connection  with  any  pre-existing  land,  but  to  grow  up  from  an  un- 
fathomable bottom.  These  latter,  by  their  singularity  and  extreme 
beauty,  have  always  attracted  the  attention  and  excited  the  wonder  of 
Pacific  travelers ;  and  to  their  explanation  theories  have  been  princi- 
pally addressed. 

Crater  Theory. — This  theory  supposes  that  an  atoll  is  an  extinct 
submarine  volcano,  the  lagoon  being  the  crater  and  the  reef  the  lip  or 
margin  of  the  crater ;  that  corals  finding  on  this  circular  rim  the  con- 
ditions of  depth  necessary  for  their  growth,  occupy  and  build  upon  it  to 
the  surface  of  the  water,  after  which,  of  course,  waves  finish  the  work 
by  beating  up  the  islets.  The  incredible  supposition  that  thousands  of 
these  volcanoes  should  have  come  within  100  feet  of  the  surface,  and 
yet  none  of  them  appear  above  the  surface,  is  not  necessary ;  for  we 
may  suppose  that  many  of  them  were  originally  above  the  surface, 
but,  being  composed  of  ashes  and  cinders,  have  been  washed  down  by 
the  waves.  In  1831  a  volcano  burst  forth  in  the  Mediterranean  and 
quickly  formed  an  island  of  cinders  and  ashes,  called  Graham's  Island. 
In  a  few  months  this  island  was  entirely  washed  away  by  the  waves, 
and  only  a  circular  submarine  bank  remained.  If  corals  grew  in  the 
Mediterranean,  there  seems  no  reason  why  a  circular  reef  should  not 
have  been  formed. 

Objections. — Even  in  its  most  plausible  form,  however,  this  theory 
is  very  improbable  as  a  general  explanation  of  atolls :  1.  The  great 
size  of  some  of  these  atolls — thirty,  sixty,  and  even  ninety  miles  in 
diameter ;  and,  2.  The  high  angle  of  the  slope  of  these  submarine 
mountains — 50°  to  60°  or  more — seem  inconsistent  with  their  volcanic 
origin.  3.  This  theory  offers  no  explanation  of  the  barrier  reefs,  and 
yet  it  is  possible  to  trace  every  stage  of  gradation  between  barriers  and 
atolls,  showing  that  they  are  due  to  similar  causes. 

Subsidence  Theory  of  Darwin. — This  theory  explains  not  only 
atolls,  but  also  barriers,  and  connects  both  in  a  satisfactory  manner 
with  fringing  reefs.  It  supposes  that  the  sea-bottom,  where  atolls  and 
barriers  occur,  has  been  for  ages  subsiding,  but  at  a  rate  not  greater 


THEORIES  OF  BARRIER  AND   CIRCULAR   REEFS. 

than  the  upward  building  of  the  coral-ground ;  that  every  reef  com- 
mences as  a  fringing  reef,  but,  in  the  progress  of  subsidence,  was  con- 
verted first  into  a  barrier  and  finally  into  an  atoll.  For,  as  the  vol- 
canic island  went  down,  the  corals  would  build  upward  on  the  same 
spot ;  and  as  the  island  would  become  smaller  and  smaller,  and  the 
corals  would  grow  faster  on  the  outer  side  of  the  reef,  where  they  are 
exposed  to  the  breakers,  it  is  evident  that  the  reef  would  become  sepa- 
rated from  the  island  by  a  ship-channel,  and  thus  become  a  barrier. 
Finally,  when  the  island  disappears  entirely,  the  reef,  still  building 
upward,  would  become  an  atoll.  These  changes  are  represented  in 
the  accompanying  section  (Fig.  125).  As  the  changes  are  relative, 
they  may  be  represented  either  by  the  land  sinking  or  the  sea-level  ris- 
ing ;  for  the  sake  of  convenience  we  use  the  latter.  In  the  figure,  I"  I" 
represents  the  sea-level  when  the  reef  was  &  fringe,  I'  I'  when  it  was  a 
barrier,  and  1 1  the  present  sea-level,  when  it  has  become  an  atoll.  The 
ship-channel  and  the  lagoon,  though  always  lower,  rise  pari  passu  with 
the  reef  proper.  This  is  the  result  partly  of  the  growth  of  placid- water 
species  of  corals,  and  partly  of  the  drifting  of  coral  debris  from  the 
reef,  and  detritus  from  the  volcanic  island.  It  is  seen  that  the  corals 
do  not  build  a  vertical  wall,  and  therefore  that  the  atoll  is  always 
smaller  than  the  coast-line  of  the  original  island.  Consequently,  if  the 
subsidence  continues,  a  typical  atoll  is  changed  into  a  small  closed 
lagoon,  and,  finally,  into  a  lagoonless  island.  These,  therefore,  indicate 
the  deepest  subsidence. 

3L Jfc. 


FIG.  125. 


Evidences. — 1.  This  theory  accounts  for  all  the  more  obvious  phe- 
nomena of  atolls,  such  as  their  irregular  circular  form,  their  size,  the 
steepness  of  their  outer  slopes,  etc.  2.  Every  stage  of  gradation  between 
the  fringing  reef  on  the  one  hand,  and  the  atoll  on  the  other,  has  been 
traced  by  Dana,  strongly  suggesting  that  they  are  all  different  stages  of 
development  of  the  same  thing.  We  have  in  the  Pacific  some  high 
islands,  which  are  surrounded  by  a  pure  fringing  reef ;  others  in  which 
the  reef  is  a  fringe  on  one  side  and  a  barrier  on  the  other ;  others  in 
which  the  barrier  is  one  mile,  two  miles,  five  miles,  ten  miles,  twenty,  or 
thirty  miles  distant ;  others  which  are  called  atolls,  but  the  point  of  the 
original  volcanic  island  is  still  visible  in  the  middle  of  the  lagoon ;  others 


152  ORGANIC  AGENCIES. 

which  are  perfect  atolls,  but,  by  sounding,  the  head  of  the  drowned  vol- 
canic island  is  still  detectable.  The  next  step  in  the  series  is  the  perfect 
atoll,  then  the  small  atoll,  and,  finally,  the  lagoonless  coral  island.  These 
last  kinds  show  that  the  original  island  has  gone  down  deeply.  3.  By 
grappling-hooks  dead  coral-trees  have  been  broken  off  and  brought  up 
from  the  ground  where  they  once  grew,  now  far  below  the  limiting 
depth  of  coral-growth.  The  evidence  of  subsidence  in  this  case  is  of  the 
same  kind  and  force  as  that  derived  from  the  submerged  forest-ground 
(page  136).  The  corals  have  been  carried  below  their  depth  and  drowned. 
4.  The  remarkable  distribution  of  the  various  kinds  of  reefs  brought  to 
light  by  Dana  is  satisfactorily  explained  by  this  theory,  and  therefore  is 
an  argument  in  its  favor.  In  the  middle  of  the  atoll  region  of  the  Pa- 
cific there  is  a  blank  area,  2,000  miles  long  and  1,000  or  more  miles 
wide  where  there  are  no  islands.  Next  about  this  is  an  area  in  which 
small  atolls  predominate  ;  about  this  again  the  region  of  ordinary  atolls ; 
beyond  this  the  region  mostly  of  barriers,  and  finally  of  fringes.  Now, 
by  this  theory  this  distribution  is  thus  explained :  The  sea-bottom  in 
the  blank  area  has  gone  down  so  fast  that  the  corals  have  not  been  able 
to  keep  pace,  and  have  therefore  been  drowned,  and  left  no  monu- 
ment of  their  existence.  In  the  next  region  the  corals  have  been  able 
to  keep  within  living  distance  of  the  surface,  but  the  original  islands 
have  not  only  disappeared,  but  gone  down  to  great  depths.  In  the 
next  the  original  high  islands  have  disappeared,  but  not  gone  down  so 
deep ;  in  the  next  they  have  sunk  only  to  the  middle.  The  fringing 
reefs  stand  on  the  margin  of  the  sinking  area.  Outside  of  this  again 
there  is  in  some  places  even  evidence  of  upheaval  instead  of  subsidence. 
Raised  beaches  in  the  form  of  fringing- reef  rocks  are  found  clinging 
to  the  sides  of  high  islands  many  feet  above  the  present  sea-level.  5. 
In  some  places  this  subsidence  seems  to  be  still  in  progress.  On  cer- 
tain coral  islands  sacred  structures  of  stone  made  by  the  natives  are 
now  standing  in  water,  and  the  paths  worn  by  the  feet  of  devotees  are 
now  passages  for  canoes  (Dana). 

Murray's  Theory. — Recently  serious  doubts  have  been  cast  on  Dar- 
win's subsidence  theory,  at  least  as  a  universal  explanation  of  barriers 
and  atolls.*  Mr.  Murray,  from  his  observations  during  the  voyage  of 
the  Challenger,  believes  that  barriers  and  atolls  may  be  explained  with- 
out subsidence  of  the  sea-floor.  An  outline  of  his  views  may  be  thus 
stated :  1.  Submarine  banks  formed  in  any  way,  either  (a)  built  up  by 
accumulating  shells  of  successive  generations  of  marine  animals,  until 
within  the  reach  of  coral-growth ;  or  (b)  by  volcanic  cinder  cones  cut 


*  The  author  of  this  volume  believes  that  he  was  the  first  who  showed,  in  the  case  of 
the  Florida  reefs,  how  barriers  may  be  formed  without  subsidence.  American  Journal 
of  Science  and  Art,  vol.  xxiii,  p.  46,  January,  1867. 


THEORIES   OF   BARRIER  AND   CIRCULAR   REEFS.  153 

down  by  the  waves  so  as  to  form  suitable  banks.  2.  The  banks  taken 
possession  of  by  corals  are  built  up  to  the  sea-level.  3.  The  coral- 
growth  is  confined,  or  at  least  most  rapid,  on  the  outer  margin,  because 
exposed  to  the  action  of  the  sea.  Thus  arises  a  ring  with  blank  space 
within.  4.  The  action  of  waves  beats  these  rings  into  a  series  of 
islets.  5.  Meanwhile  the  scouring  action  of  currents  and  the  solvent 
action  of  sea- water,  scoops  out  the  blank  area  into  a  more  or  less  deep 
lagoon.  6.  The  action  of  waves  breaking  the  living  coral  and  the  reef- 
rock  forms  a  debris-pile  or  talus,  with  steep  outward  slope,  on  which 
the  corals  continue  to  grow  seaward  into  deep  water.  Thus  the 
coral  ring  continues  to  spread,  like  a  fairy  ring,  by  growing  seaward 
in  every  direction  and  dying  behind.  7.  According  to  Darwin,  atolls 
grow  continually  smaller ;  according  to  Murray,  they  grow  continually 
larger. 

Barriers  are  similarly  explained.  They  commence  as  fringes,  which 
grow  seaward  as  far  as  depth  will  allow.  Then  the  corals  die  near 
the  shore,  and  this  part  is  scoured  out  into  a  channel.  Meanwhile 
the  reef  extends  seaward  on  its  own  talus,  and  the  channel  is  pari 
passu  widened. 

In  the  present  condition  of  the  question  it  is  probable  that  there 
are  more  ways  than  one  in  which  barriers  and  atolls  may  be  formed, 
but  Darwin's  view  seems  still  to  hold  its  own  as  a  generaly  though  not 
as  a  universal  theory. 

On  Darwin's  view,  of  course,  every  atoll  marks  the  site  of  a  sunken 
volcanic  island.  It  will  be  interesting,  therefore,  to  make  some  esti- 
mates based  on  this  view. 

Area  of  Land  lost. — Probably  several  hundred  thousand  square 
miles  of  habitable  high  land  has  been  lost  by  this  subsidence.  The 
actual  extent  of  atolls  known  is  at  least  50,000  square  miles.  But  this 
is  far  less  than  the  loss  of  high  land.  For — 1.  It  is  certain  that  the 
area  of  an  atoll  is  always  less  than  that  of  the  original  fringe  or  base  of 
the  original  high  island,  for  the  outer  wall  of  an  atoll  is  not  perpendicu- 
lar. The  contraction  continues  as  the  subsidence  progresses,  until 
small  atolls  or  only  lagoonless  islands  remain.  2.  An  immense  lost 
area  is  represented  by  the  space  between  barriers  and  their  high  isl- 
ands. The  great  Australian  barrier  extends  along  that  coast  1,100 
miles,  at  an  average  distance  of  thirty  miles,  with  a  ship-channel  be- 
tween of  thirty  to  sixty  fathoms  deep.  This  single  barrier,  therefore, 
represents  a  lost  land-area  of  33,000  square  miles.  3.  In  the  blank 
area  already  spoken  of,  probably  many  islands  went  down,  and  left  no 
record  behind. 

The  large  amount  of  high  land  thus  lost  has  been  replaced  only  to 
a  small  extent  by  the  wave-formed  coral  islets  on  the  reefs. 

Amount  of  Vertical  Subsidence. — The  amount  of  subsidence  may  be 


154:  ORGANIC  AGENCIES. 

estimated  by  the  distance  of  barriers  from  their  high  islands,  or  by 
soundings  off  atolls,  to  ascertain  the  height  of  these  coral  mounds, 


FIG.  126. 


or  by  the  average  height  of  the  high  islands  of  the  Pacific.  1.  The 
average  slope  of  the  high  islands  of  the  Pacific  is  about  8°.  Now,  as- 
suming this  slope  (Fig.  126),  a  barrier,  <#,  at  the  distance  of  five  miles 
would  be  3,700  feet  thick,  and  would  represent  a  subsidence  nearly  to 
that  extent  (Rad. :  tan.  8°  : :  adidb);  a  distance  of  ten  miles  would 
represent  a  vertical  subsidence  of  7,400  feet.  Many  barriers  are  at  much1 
greater  distance.  2.  Off  Keeling  atoll  6,600  feet,  a  line  of  7,200  feet 
found  no  bottom  (Darwin).  Near  other  atolls  a  depth  of  3,000  feet  has 
been  found  (Dana).  3.  The  average  height  of  the  high  islands  of  the 
Pacific  can  not  be  less  than  9,000  feet  (Dana) ;  some  of  them  reach 
nearly  14,000  feet.  It  is  very  improbable  that,  among  the  hundreds  of 
atolls  known,  not  one  of  their  high  islands  should  have  reached  the 
average  elevation  of  9,000  feet.  Yet  these  have  entirely  disappeared, 
and  not  only  so,  but  the  small  atolls  and  lagoonless  islands,  and  more 
especially  the  blank  area,  would  seem  to  indicate  that  they  have  disap- 
peared to  great  depths.  For  these  reasons,  it  is  almost  certain  that  the 
extreme  subsidence  has  been  at  least  9,000  feet.  We  will  take  10,000 
feet  as  the  most  probable  extreme  subsidence. 

Rate  of  Subsidence. — The  rate  of  subsidence  may  have  been  to  any 
degree  less,  but  can  not  have  been  greater,  than  the  rate  of  coral  ground- 
rising  ;  for  otherwise  the  corals  would  have  been  carried  below  their 
depth  and  drowned.  It  is  difficult  to  estimate  the  rate  of  coral  ground- 
rising,  but  the  only  basis  of  such  estimate  is  the  rate  of  coral-growth. 
Of  the  observations  on  this  point  we  select  two,  one  of  them  on  the 
head-coral  (meandrina),  the  other  on  the  staghorn- coral  (madrepore) : 

1.  On  the  walls  of  the  fort  at  the  Tortugas,  Florida,  meandrina  com- 
menced to  grow,  and  in  fourteen  years  the  crust  had  become  only  one 
inch  thick.     Agassiz  takes  one  inch  in  eight  years  as  a  probable  rate 
under  favorable  circumstances.     This  would  be  one  foot  in  a  century. 
As  this  is  a  head-coral,  the  coral-growth  may  be  taken  as  the  measure 
of  the  reef  ground-rising. 

2.  In  examining  the  reefs  about  the  Tortugas  in  the  winter  of  1851, 
an  extensive  grove  of  madrepore  was  found  in  the  comparatively  still 
water  on  the  inside  of  the  outer  reef,  in  which  the  thick-set  prongs  had 
grown,  year  after  year,  to  the  same  level,  and  were  successively  killed. 
The  mean  level  of  the  water  here  is  lower  during  the  winter,  by  about 


THEORIES   OF  BARRIER  AND   CIRCULAR   REEFS.  155 

a  foot,  than  during  the  summer.  The  falling  of  the  water  annually 
clips  this  grove  at  the  same  level.  Now  all  the  prongs  at  this  level 
were  dead  for  about  three  inches.  Evidently,  therefore,  this  is  the  an- 
nual growth  of  madrepore-prongs.*  But  in  branching  corals  the  rate 
of  point-growth  is  very  different  from  the  rate  of  ground-rising.  If  all 
the  points  of  a  madrepore  be  cut  off  three  inches,  then  ground  into 
powder,  and  the  powder  strewed  evenly  over  the  ground  shaded  by 
the  coral-tree,  the  elevation  thus  produced  would  correctly  represent 
the  annual  rate  of  reef  ground-rising  for  this  species.  A  quarter  of  an 
inch  would  probably  be  a  full  estimate.  This  would  make  two  feet  for 
a  century.  One  foot  to  two  feet  per  century  is,  therefore,  probably 
about  the  rate  at  which  coral  ground  rises.  As  already  stated,  the  rate 
of  subsidence  may  be  less,  but  can  not  be  greater,  than  this. 

Time  involved. — At  this  rate  10,000  feet  of  vertical  subsidence  would 
require  500,000  to  1,000,000  years.  How  much  of  this  belongs  to  the 
present  geological  epoch  it  is  impossible  to  say.  Dead  corals,  identical 
with  those  still  living  on  the  reefs,  have  been  brought  up  from  a  depth 
of  250  feet,  but,  as  this  is  only  150  feet  below  the  limit  of  coral-growth, 
it  would  require  only  75  to  150  centuries.  The  process  probably  com- 
menced in  previous  geological  epochs,  and  has  continued  to  the  present 
time.  This  is,  therefore,  an  admirable  example  of  geological  agencies 
still  at  work. 

Geological  Application. — The  facts  brought  out  in  the  preceding 
pages  are  of  great  importance  in  geology. 

1.  We  have  here  the  most  magnificent  example  of  subsidence  still 
in  progress.  The  subsiding  area  has  not  been  accurately  defined,  but 
it  probably  covers  nearly  the  whole  of  the  intertropical  Pacific.  Ac- 
cording to  Dana,  estimated  by  the  atolls  alone,  it  is  6,000  miles  long 
and  2,000  miles  wide ;  but  if  we  take  into  account  also  barriers,  which 
are  equally  certain  evidences  of  subsidence,  it  extends  east  and  west 
from  the  extreme  of  the  Paumotu  group  on  the  one  side  to  the  Pelews 
on  the  other,  and  north  and  south  from  the  Hawaiian  group  to  the  Fee- 
jees,  making  an  area  of  not  less  than  20,000,000  square  miles.  Now,  it 
is  evident  that  there  must  have  been,  as  a  correlative  of  this  extensive 
and  permanent  downward  movement,  an  equally  extensive  permanent 
elevation  of  the  earth's  crust  somewhere  else.  Dana  thinks  its  correla- 
tive is  found  in  the  extensive  elevations  of  the  Glacial  epoch,  and  there- 
fore that  the  whole  work  was  accomplished  since  the  Tertiary.  But  it 
is  more  probable  that  its  correlative  is  found  in  the  gradual  bodily 
upheaval  of  the  whole  western  side  of  the  continent,  especially  in  the 
Rocky  Mountain  region,  which  commenced  after  the  Cretaceous. 

*  See  full  account  of  these  observations  in  American  Journal  of  Science  and  Arts,  vol. 
x,  p.  34. 


156 


ORGANIC   AGENCIES. 


2.  We  have  here  the  formation  of  limestone  rocks  of  various  kinds 
going  on  before  our  eyes  over  immense  areas  and  several  thousand  feet 
in  thickness,  and  we  learn  thus  that  limestones  are  of  organic  origin. 

3.  The  character  of  the  rocks  thus  formed  is  very  interesting  to 
the  geologist.     In  some  places,  as  we  have  already  seen,  it  is  a  coarse 
conglomerate,  or  breccia,  composed  of  fragments  of  all  sizes  cemented 
together ;  in  some  places  it  is  made  up  entirely  of  rounded  granules  of 
coralline  limestone  (coral-sand),  cemented  together,  and  forming  a  pe- 
culiar oolitic  rock  (wov  Ai0os,  egg-stone).      But  the  larger  portion  of 
the  reef  ground  is  a  fine  compact  limestone,  made  up  of  comminuted 
coralline  matter  (coral  mud),  cemented  together.     This  fine  coral  mud 
is  carried  by  waves  and  tides  into  the  lagoon,  and  serves  to  raise  its 
bottom :  it  is  also  carried  by  currents  and  distributed  widely  over  the 
neighboring  sea-bottoms.     Soundings  in  coral  seas  bring  up  everywhere 
this  final  coral  mud,  showing  that  compact  limestone  is  now  forming 
over  wide  areas  in  coral  seas.     The  reef -rock,  as  already  stated,  has  been 
found  clinging  to  the  sides  of  high  islands,  having  been  elevated  many 
feet  above  sea-level ;  in  other  cases  atolls  have  been  elevated  250  feet 
above  the  sea-level.     The  structure  of  the  reef-rock  has  thus  been  ex- 
posed to  view.     In  some  places  it  contains  imbedded  remains  of  corals 
and  shells,  but  in  other  parts  it  is  entirely  destitute  of  these  remains. 


Reefs  of  Florida. 


FIG.  127. — Map  of  Florida  with  its  Keys  and  Reefs,     a,  Southern 
coast;  a',  Keys;  a".  Living  reef:  e,  Everglades;  e',  Shoal  water; 


e",  Ship-channel;  G  S  S,  Gulf  Stream. 


The  reefs  of  Flor- 
ida deserve  a  brief 
separate  notice,  both 
because  they  are  dif- 
ferent from  those  of 
the  Pacific,  having 
been  formed  under 
different  conditions, 
and  because  they  are 
much  more  efficient 
agents  in  land-mak- 
ing, and  illustrate  in 
a  striking  manner 
how  different  agen- 
cies co-operate  for 
this  purpose.  The 
process  has  been  ac- 
curately observed. 

Description  of 
Florida.— Fig.  127  is 
a  map  of  Florida, 


REEFS  OF  FLORIDA. 


157 


with  its  reefs  and  keys,  and  Fig.  128  is  a  section  along  the  line  N  S. 
The  southern  coast  (a  a)  is  ridge,  elevated  twelve  to  fifteen  feet  above 
the  sea-level,  within  which  is  the  Everglades  (e)  an  extensive  fresh- 
water swamp  only  two  or  three  feet  above  sea-level,  and  dotted  over  with 
small  islands  called  hummocks.  Between  the  southern  coast  (a  a)  and 
the  line  of  keys  (a*  a')  the  water  (e')  is  very  shallow,  only  navigable  to 
smallest  fishing-craft,  and  dotted  over  with  small  low  mangrove  islands. 


Fin.  128.— Section  of  same  along  line  ITS.    Letters  indicate  the  same.    The  dotted  lines  show  sup- 
posed previous  conditions. 

A  considerable  portion  of  this  area,  in  fact,  forms  mud-flats  at  low  tide. 
Between  the '  line  of  keys  (a1  a')  and  the  living  reef  (a"  a")  there  is  a 
ship-channel  (e")  five  to  six  fathoms  deep.  Outside  the  reef  (a"  a")  the 
bottom  slopes  rapidly  into  the  almost  unfathomable  abyss  of  the  Gulf 
Stream  (O  88). 

General  Process  of  Formation. — Now,  Agassiz  *  has  proved  that  not 
only  the  living  reef  but  the  keys,  the  southern  coast,  and  the  peninsula, 
certainly  as  far  north  as  the  north  shore  of  the  Everglades  (d  d),  and 
probably  on  the  east  side  as  far  north  as  St.  Augustine  (^'),  have  been 
formed  by  coral  agency.  The  evidence  of  this  important  conclusion 
is  that  the  rock  in  all  these  parts  is  identical  with  the  reef -rock  already 
described,  and  with  what  is  even  now  forming  under  our  eyes  on  the  liv- 
ing reef  (a"  a").  It  is,  moreover,  almost  certain  that  the  peninsula  of 
Florida  has  been  progressively  elongated  by  the  formation  of  successive 
barrier  reefs,  one  outside  of  the  other,  from  the  north  toward  the  south, 
and  the  successive  filling  up  of  the  intervening  ship-channels,  probably 
by  coral  debris  from  the  reef  and  sediments  from  the  mainland. 

History  of  Changes  — The  history  of  changes  was  as  follows :  There 
was  a  time  when  the  north  shore  of  the  Everglades  (d  d)  was  the  south- 
ern limit  of  the  peninsula.  At  that  time  the  ridge  (a  a)  which  now 


*  Coast  Survey  Report  for  1851,  p.  145  et  seq. 


158  ORGANIC  AGENCIES. 

forms  the  south  shore  was  a  reef.  Upon  this  reef  by  the  action  of  waves 
was  gradually  formed  a  line  of  coral  islands,  which  finally  coalesced  into 
a  continuous  line  of  land,  and  by  the  filling  up  of  the  intervening  ship- 
channel  was  added  to  the  peninsula,  the  ship-channel  being  converted 
into  the  present  Everglades.  In  the  mean  time  another  reef  was  formed 
in  the  position  of  the  present  line  of  keys.  This  has  already  been  con- 
verted into  a  line  of  wave-formed  islands,  and  its  ship-channel  into  shoal 
water  and  mud-flats.  Eventually  the  peninsula  will  be  extended  to  the 
line  of  keys,  and  the  shoal  water  (er)  will  become  another  Everglades 
and  the  mangrove  islands  its  hummocks.  Already  another  reef  has 
been  again  formed  outside  the  last,  viz.,  the  present  living  reef  (a"  a"), 
and  upon  it  the  process  of  island-formation  has  commenced.  This  will 
also  be  eventually  converted  into  a  line  of  keys,  into  a  continuous  line 
of  land,  and  be  added  in  its  turn  to  the  peninsula.  It  is  not  probable 
that  another  reef  will  be  formed  outside  of  this,  for  the  bottom  slopes 
rapidly  under  the  Gulf  Stream,  as  seen  in  the  section  Fig.  128.  In 
this  process  each  reef  dies  when  another  is  formed  beyond  it,  for  the 
water  being  protected  by  the  outside  reef  becomes  placid  or  lagoon 
water,  and  the  strong  reef-building  species  no  longer  flourish. 

North  of  the  line  d  d  the  evidence  is  of  the  same  kind,  but  less 
complete.  True  reef-rock,  similar  to  that  now  forming  on  the  reef, 
has  been  found  at  various  points  as  far  north  as  St.  Augustine,  on 
the  eastern  shore.  The  western  shore  and  interior  are  less  known. 
Tuomey  in  1850  traced  the  Eocene  on  the  west  side  as  far  as  Tampa,* 
and  Smith  in  1880  even  to  the  north  shores  of  the  Everglades.f 
The  heavily  shaded  part,  therefore,  gives  the  probable  outline  of  the 
peninsula  at  the  end  of  the  Tertiary.  If,  however,  as  asserted  by  Agassiz, 
superficial  patches  of  coral,  of  species  identical  with  those  still  on  the 
reefs,  are  found  over  this  region,  there  must  have  been  at  least  a  tem- 
porary submergence  during  the  Quaternary. 

Mangrove  Islands. — Mangrove-trees  co-operate  in  an  interesting 
manner  with  corals  in  the  process  of  land -formation.  These  trees 
form  dense  jungles  on  the  low,  muddy  shores  of  tropical  regions. 
They  are  very  abundant  on  the  shores  of  Florida.  They  have  the  re- 
markable power  of  throwing  out  aerial  roots  from  their  trunks  and 
branches,  thus  forming  subordinate  connections  with  the  ground  or 
with  the  bottom  of  shallow  water.  From  these  may  spring  other 
trunks,  which  throw  out  similar  roots,  etc.  Thus  an  inextricable  en- 
tanglement of  roots  and  branches  continues  to  extend  far  beyond  the 
actual  shore-line.  These  form  a  nidus  for  the  detention  of  sediments, 
and  protect  them  from  the  action  of  waves ;  and  the  shore-line  thus, 
steadily  advances. 

*  American  Journal  of  Science,  vol.  i,  p.  390,  1850.  f  Ibid.,  vol.  xxi,  p.  292,  1881. 


REEFS  OF  FLORIDA.  159 

The  seeds  of  the  mangrove  have  also  the  faculty  of  shooting  out 
long  roots  and  stems,  even  while  still  attached  to  the  parent  tree. 
These  sprouted  seeds,  falling  into  the  water,  float  away,  and  if  their 
roots  touch  bottom  immediately  fix  themselves,  grow  into  mangrove- 
trees,  and  commence  multiplying  in  the  manner  described.  Thus  in 
the  shoal  water  (er)  are  found  mangrove  islands  in  which  there  is  no 
land,  but  only  a  mangrove  forest,  standing  above  water  by  means  of 
their  interlaced  roots.  By  these,  however,  sediments  are  detained,  and 
a  true  island  is  speedily  formed.  It  is  in  this  way  that  the  small  man- 
grove islands  in  the  shoal  water  on  the  south  and  west  of  Florida  are 
formed.  They  are  entirely  different  from  the  wave-formed  coral  isl- 
ands or  keys.  The  hummocks  in.  the  Everglades  have  probably  a 
similar  origin,  although  some  of  them  may  possibly  be  of  coral 
origin. 

Florida  Reefs  compared  with  other  Reefs. — In  comparing  the  reefs 
just  described  with  other  reefs,  it  will  be  seen  that  the  former  are 
unique  in  two  respects. 

No  other  reefs  continuously  make  land.  In  fringing  reefs  there  is 
a  small  accretion  about  the  shore-line  of  the  previously-existing  land, 
but  this  process  is  quickly  limited.  In  barriers  and  atolls,  according 
to  Darwin,  there  is  always  loss  of  land,  only  a  small  fraction  of  which 
is  recovered  by  coral  and  wave  agency.  But  under  these  agencies 
Florida  has  steadily  advanced  southward  more  than  100  miles,  and  the 
area  thus  added  to  the  continent  is  at  least  10,000  square  miles.  It 
seems  utterly  impossible  to  account  for  this,  except  by  supposing  some 
other  agency  at  work  preparing  the  ground  for  the  growth  of  success- 
ive reefs. 

Probable  Agency  of  the  Gulf  Stream. — Since  corals  can  not  grow  in 
water  more  than  sixty  to  one  hundred  feet  deep,  it  is  evident  that,  un- 
less subsidence  goes  on  pari  passu  with  the  growth  of  the  corals,  a  coral 
formation  can  not  be  more  than  one  hundred  feet  thick.  But  there  is  no 
evidence  of  subsidence  on  the  coast  or  keys  of  Florida.  On  the  contrary, 
the  height  of  these  parts  is  precisely  the  usual  height  of  wave-formed 
islands,  although  no  longer  exposed  to  their  action.  It  follows,  there- 
fore, that  the  corals  must  have  built  upon  an  extensive  submarine  bank, 
produced  by  some  other  agency.  Furthermore,  since  the  reefs  were 
formed  successively  one  beyond  another,  it  is  evident  that  there  must 
have  been  a  progressive  formation  of  this  bank  from  the  north  toward 
the  south.  T/te  dotted  lines  (Fig.  128)  show  successive  positions  of  the 
lanlc  of  the,  reefs.  Such  a  progressive  extension  of  a  bank  can  only 
be  formed  by  sedimentary  deposit.  It  is  almost  certain  that  in  some 
way  the  Gulf  Stream  is  connected  with  this  sedimentary  accumula- 
tion. It  is  to  this  agency,  therefore,  that  we  attribute  the  formation 
and  extension  of  the  bank  upon  winch  the  corals  grow. 


160  ORGANIC  AGENCIES 

At  one  time  *  the  writer  thought  that  the  bank  was  formed  and  ex- 
tended by  mechanical  sediments  brought  by  the  Gulf  Stream,  and  de- 
posited on  the  inner  side  of  its  curve ;  but  Alexander  Agassiz  has 
shown  f  that  the  sediments  are  more  probably  organic,  and  the  bank 
was  formed  partly  by  such  sediments  brought  by  the  Gulf  Stream 
from  other  coral  banks  in  the  Caribbean  Sea,  but  mostly  built  up  in 
situ  by  the  accumulation  of  shells  of  successive  generations  of  deep- 
sea  animals,  the  Gulf  StreaYn  bringing  only  the  conditions  of  rapid 
growth  in  the  form  of  warmth  and  abundant  food. 

It  is  probable,  therefore,  that  the  southern  portion  of  the  peninsula 
of  Florida  is  due  to  the  co-operation  of  four  or  five  different  agencies, 
viz. :  1.  The  Gulf  Stream  building  up  a  submarine  bank  to  the  dotted 
line  ri  ri,  Fig.  128,  within  100  feet  of  the  surface ;  2.  Then  corals 
building  up  to  the  surface ;  3.  Then  waves  raising  it  twelve  to  fifteen 
feet  above  the  surface ;  4.  And,  finally,  debris  from  the  peninsula,  on 
the  one  side,  and  the  reef  and  keys  on  the  other,  filling  up  the  inter- 
vening channels,  and  afterward  raising  the  level  of  the  swamps  or 
Everglades  thus  formed ;  5.  In  this  last  process  the  mangrove-trees 
have  assisted. 

2.  The  reefs  of  Florida  are  barrier  reefs.  Barriers  are  usually  sup- 
posed to  indicate  subsidence.  The  Pacific  barriers,  according  to  Dar- 
win, commenced  as  fringes  and  became  barriers  by  subsidence.  But 
in  Florida  there  has  been  no  subsidence.  They  did  not  commence  as 
fringes.  The  probable  explanation  is  this :  Corals  will  not  grow  in 
muddy  water.  On  a  gently-sloping  shore  with  mud  bottom,  such  as 
probably  always  existed  on  the  southern  shore  of  Florida,  a  fringing 
reef  could  not  form,  because  the  bottom  would  be  always  chafed  by  the 
waves  and  the  water  rendered  turbid.  But  at  a  distance  from  shore, 
on  the  edge  of  the  bank,  where  such  a  depth  was  attained  that  the 
waves  no  longer  chafed  the  bottom,  a  barrier  would  form,  limited  on 
the  one  side  by  the  muddiness,  and  on  the  other  by  the  depth,  of  the 
water.  Also  the  proximity  of  the  Gulf  Stream,  carrying  warmth  and 
food,  would  contribute  to  the  same  result. 

It  will  be  observed  that  this  view  of  the  formation  of  barriers  differs 
from  both  that  of  Darwin  and  that  of  Murray.  It  has  been  adopted 
by  Captain  Guppy  for  some  of  the  barriers  of  the  Pacific.  J 

Shell-Deposits. 

Eivers  carry  carbonate  of  lime  in  solution  to  the  sea  (p.  82).  In 
some  bays,  where  large  quantities  of  this  material  are  carried  by  rivers 

*  American  Journal  of  Science,  Second  Series,  vol.  xxiii,  p.  46,  1857. 
f  Memoirs  of  the  American  Academy  of  Science,  vol.  xi,  p.  107. 
t  Nature,  vol.  xxxv,  p.  77,  1886. 


SHELL-DEPOSITS.  161 

running  through  limestone  countries,  the  excess  may  be  deposited  as  a 
chemical  deposit.  But  in  most  cases  sea-water  contains  less  lime-car- 
bonate than  river- water.  The  reason  is,  that  the  lime-carbonate  in  sea- 
water  is  continually  being  drafted  upon  by  organisms  and  deposited  on 
their  death  as  organic  limestones.  We  have  already  shown  how  coral 
limestone  is  thus  formed.  But  there  are  many  other  limestone-forming 
animals,  and  some  species  form  other  kinds  of  deposits  besides  lime- 
stone. 

Molluscous  Shells. — Shallow-water  deposits  of  this  kind  are  made 
principally  by  mollusca  which,  living  in  immense  numbers  near  shore 
and  on  submarine  banks,  leave  their  dead  shells  generation  after  gener- 
ation, and  thus  form  sometimes  pure  shelly  deposits,  and  sometimes 
shells  mingled  with  sediments  due  to  other  agencies.  On  quiet  shores 
the  shells  are  quite  perfect,  whether  imbedded  in  mud  or  forming  shell- 
banks  like  our  oyster-banks ;  but  when  exposed  to  the  action  of  break- 
ers, they  are  broken  into  coarse  fragments,  or  even  comminuted,  worn 
into  rounded  granules,  and  cemented  into  shell-rock  or  oolitic  rock. 
Such  shell-rock  and  oolitic  rock  are  now  being  formed  on  the  coast  of 
the  Florida  keys  and  of  the  West  Indies.  Similar  rock  is  found  in 
every  part  of  the  world  in  the  interior  of  continents.  They  indicate 
the  existence  in  these  places  of  a  shore-line  or  of  shallow  water  in  some 
previous  geological  epoch. 

Microscopic  Shells. — Microscopic  plants  and  animals  are  known  to 
multiply  in  numbers  with  almost  incredible  rapidity.  Many  of  them 
form  no  shell,  and  therefore  are  of  no  geological  importance ;  but  many 
species  form  shells  of  silica  or  of  carbonate  of  lime,  and  these  of  course 
accumulate  generation  after  generation,  until  important  deposits  are 
formed. 

Fresh-water  Deposits. — In  streams,  ponds,  lakes,  and  hot  springs, 
the  beautiful  siliceous  shells  of  diatoms  (uni-celled  plants)  accumulate 
without  limit.  '  The  ooze  at  the  bottom  of  clear  ponds,  or  lakes,  as,  for 
example,  in  the  deepest  parts  of  Lake  Tahoe,  consists'  of  ten  wholly  of 
these  shells.  Diatoms  live  also  in  great  numbers  in  the  hot  springs  of 
California,  Nevada,  and  Yellowstone  Park,  and  the  deposits  of  such 
springs  sometimes  consist  wholly  of  these  shells,  and  in  Yellowstone 
Park  cover  many  square  miles,  and  are  five  to  six  feet  thick.*  Thick 
strata,  belonging  to  earlier  geological  times,  are  found  wholly  composed 
of  diatoms.  We  are  thus  able  to  explain  the  formation  of  these  strata. 

Deep-sea  Deposits. — Over  nearly  all  the  bottom  of  deep  seas,  be- 
yond the  reach  of  sedimentary  deposits,  we  find  a  white,  sticky  ooze, 
composed  of  the  carbonate-of-lime  shells  of  microscopic  animals  (fora- 
minifers),  Fig.  129,  and  microscopic  plants  (coccospheres).  Some  of 

*  Weed,  Botanical  Gazette,  May,  1889. 
11 


162 


ORGANIC  AGENCIES. 


these  seem  to  be  living,  or  recently  dead ;  some  dead  and  empty,  but 
still  perfect ;  but  most  of  them  completely  disintegrated.  On  account 
of  the  great  abundance  of  the  shells  of  one  form  of  foraminifera,  this 


FIG.  129.— Shells  of  living  Foraminifera :  a,  Orbulina  universa,  in  its  perfect  condition,  showing 
the  tubular  spines  which  radiate  from  the  surface  of  the  shell;  b,  &lobigerina  bulloides,  in  its 
ordinary  condition,  the  thin  hollow  spines  which  are  attached  to  the  shell  when  perfect  having 
been  broken  off;  c,  Textularia  variabilis  ;  d,  Peneroplis  planatus  ;  e,  Eotalia  concamerata  ;  J, 
Cristellaria  subarcuatuta.  Fig.  a  is  after  Wyville  Thomson;  the  others  are  after  Williamson. 
All  the  figures  are  greatly  enlarged  (after  Nicholson). 

soft,  white  mud  is  called  gloligerina  ooze.  Mingled  in  considerable 
numbers  among  the  calcareous  shells  are  others  of  silica.  These  are 
also  partly  animals  (radiolaria)  and  partly  plants  (diatoms).  The  ex- 
traordinary resemblance  of  this  deep-sea  ooze,  both  in  chemical  and 
microscopic  character,  to  chalk,  leaves  no  room  for  doubt  that  chalk 
was  formed  in  this  way. 


PAET  II. 
STRUCTURAL  GEOLOGY. 


WE  have  thus  far  studied  causes  now  in  operation  or  dynamical 
principles.  We  now  study  the  structure  of  the  earth  (which  is  the 
effect  of  the  same  accumulated  throughout  all  geological  time),  and 
the  application  of  the  foregoing  principles  in  its  explanation.  The 
subject  of  this  part,  therefore,  is  both  structural  and  dynamical  ge- 
ology. 


CHAPTER  I. 
GENERAL  FORM:  AND  STRUCTURE  OF  THE  EARTH. 

1. — Form  of  the  Earth. 

THE  form  of  the  earth  is  that  of  an  oblate  spheroid  flattened  at  the 
poles.  The  polar  diameter  is  less  than  the  equatorial  diameter  by 
about  twenty-six  miles,  or  about  -gfa  °f  the  mean  diameter.*  The 
highest  mountains,  being  only  five  miles  high,  do  not  interfere  greatly 
with  the  general  form. 

This  form,  being  precisely  that  which  a  fluid  body  revolving  freely 
would  assume,  has  been  regarded  by  many  of  the  most  distinguished 
physicists  as  conclusive  evidence  of  the  former  fluid  condition  of  the 
earth.  The  argument  may  be  stated  as  follows:  1.  A  fluid  body 
standing  still,  under  the  influence  only  of  its  own  molecular  or  gravi- 
tating forces,  would  assume  a  perfectly  spherical  form ;  but,  if  rotating, 
the  form  which  it  would  assume,  as  the  only  form  of  equilibrium,  is 
that  of  an  oblate  spheroid,  with  its  shortest  diameter  coincident  with 
the  axis  of  rotation.  Now,  this  is  precisely  the  form  not  only  of  the 
earth,  but,  as  far  as  known,  of  all  the  planetary  bodies.  2.  In  an  ob- 
late spheroid  of  i  otation  the  oblateness  increases  with  the  rapidity  of 


*  More  exactly  y^-.y,  Philosophical  Magazine,  vol.  x,  p.  121,  1880. 


164-      GENERAL  FORM  AND  STRUCTURE  OF  THE  EARTH. 

rotation.  Now,  Jupiter,  which  turns  on  its  axis  in  ten  hours,  is  much 
more  oblate  than  the  earth.  The  flattening  of  the  earth  is  only  about 
3^-g-  of  its  diameter,  while  that  of  Jupiter  is  about  ^.  3.  The  forms 
of  the  earth  and  of  Jupiter  have  been  calculated ;  the  data  of  calcula- 
tion being  the  former  fluidity,  the  time  of  rotation,  and  an  assumed 
rate  of  increasing  density  from  surface  to  center ;  and  the  calculated 
form  comes  out  nearly  the  same  as  the  measured  form. 

The  force  of  this  argument,  however,  has  been,  to  say  the  least, 
greatly  exaggerated.  The  oblateness  of  the  earth  and  planets,  as  has 
been  shown  by  Playfair  and  Herschel,*  only  proves  that  they  have 
assumed  their  form  under  the  influence  of  rotation — that  they  are 
spheroids  of  rotation— but  not  that  they  have  ever  been  in  a  fluid  con- 
dition. For  since  a  rotating  body,  whatever  be  its  form,  always  tends 
to  assume  an  oblate  spheroid  form,  and  since  the  materials  on  the  sur- 
face of  the  earth  are  in  continual  motion,  being  shifted  hither  and 
thither  under  the  influence  of  atmospheric  and  aqueous  agencies,  it  is 
evident  that  the  final  and  total  result  of  such  motions  must  be  in  the 
course  of  infinite  ages  to  bring  the  earth  to  the  only  form  of  equilib- 
rium of  a  rotating  body,  viz.,  an  oblate  spheroid.  If,  for  example,  the 
earth  were  a  rigid  sphere,  standing  still  and  covered  with  water,  and  then 
set  rotating,  the  waters  would  gather  into  an  equatorial  ocean,  and  the 
land  be  left  as  polar  continents.  But  this  condition  would  not  remain ; 
for  atmospheric  and  aqueous  agencies,  if  unopposed,  would  eventually 
cut  down  the  polar  continents  and  deposit  them  as  sediments  in  the 
equatorial  seas,  and  the  solid  earth  would  thus  become  an  oblate  sphe- 
roid. This  final  effect  of  degrading  agencies  would  not  be  opposed  by 
igneous  agencies,  as  the  action  of  these  is  irregular,  and  does  not  tend 
to  any  particular  form  of  the  earth.  Yet  this  applies  only  to  the  gen- 
eral spheroidal  form ;  for  Hennessey  has  shown  f  that  although  the 
spheroidal  form  would  be  assumed  either  by  fluidity  or  by  abrasion,  yet 
the  degree  of  ellipticity  of  the  spheroid  would  be  different,  and  probably 
sensibly  different  in  two  cases,  being  greater  in  the  former ;  and  that 
the  actual  form  of  the  earth  more  nearly  approaches  this  greater  degree. 

Therefore,  although  there  are  many  reasons,  drawn  both  from  geol- 
ogy and  from  the  nebular  hypothesis,  for  believing  that  the  earth  was 
once  in  an  incandescent  fluid  condition,  and  that  it  then  assumed  an 
oblate  spheroid  form  in  obedience  to  the  laws  of  equilibrium  of  fluids ; 
yet  this  form  alone  must  not  be  assumed  as  demonstrative  proof  of 
such  original  condition,  since  a  similar  form  would  be  produced  by 
causes  now  in  operation  on  the  earth-surface,  whatever  may  have  been 
its  original  form  and  condition.  Moreover,  it  is  evident  that  the  exact 

*  Lyell,  Principles  of  Geology,  vol.  ii,  p.  199. 

f  Philosophical  Magazine,  vol.  vii,  p.  67,  1879,  vol.  x,  p.  119,  1880,  and  vol.  xi,  p. 
283,  1881. 


DENSITY  OF  THE  EARTH.  165 

original  form,  however  determined,  can  not  have  been  retained ;  for 
there  are  causes  in  operation  which  have  tended  constantly  to  modify 
it.  If  abrasion  can  produce,  it  can  also  modify  the  form  of  the  earth. 
If  the  form  of  the  earth  is  a  form  of  equilibrium,  then  a  change  in  the 
rate  of  rotation  will  produce  a  change  in  the  degree  of  oblateness  or 
ellipticity.  Now,  when  the  earth  first  solidified  from  an  incandescent 
liquid  condition,  it  had  a  certain  degree  of  ellipticity  determined  by 
its  rate  of  rotation ;  but  this  rate  of  rotation  has  not  been  constant. 
The  earth,  from  that  time  until  now,  has  been  cooling  and  contracting ; 
and  contraction  would  tend  to  accelerate  rotation  and  increase  ellip- 
ticity. But,  also,  ever  since  an  ocean  was  first  formed  by  precipita- 
tion on  the  cooling  earth,  tides  have  been  formed  by  the  moon  and 
sun,  and  ihe  friction  of  the  dragging  tides  would  tend  to  retard  rota- 
tion and  decrease  ellipticity.  At  first,  doubtless,  the  contractional 
acceleration  prevailed  and  ellipticity  increased ;  but  now  tidal  retarda- 
tion prevails,  and  ellipticity  is  probably  decreasing. 

2. — Density  of  the  Earth. 

The  mean  density  of  the  earth,  as  determined  by  several  independent 
methods,  is  about  5 -6.  The  density  of  the  materials  of  the  earth-sur- 
face, leaving  out  water,  is  only  about  2  to  2*5.  It  is  evident,  therefore, 
that  the  density  of  the  central  portions  must  be  much  more  than  5*6. 
This  great  interior  density  may  be  the  result — 1.  Of  a  difference  of  ma- 
terial. It  is  not  improbable  that  the  surface  of  the  earth  has  become 
oxidized  by  contact  with  the  atmosphere,  and  that  at  great  depths  the 
earth  may  consist  largely  of  metallic  masses.  Or  the  great  interior 
density  may  be  the  result. — 2.  Of  condensation 
by  the  immense  pressure  of  the  superincumbent 
mass.  In  either  case  the  tendency  of  increasing 
heat  would  be  to  diminish  the  increasing  densi- 
ty. But  how  much  of  the  greater  density  is  due 
to  difference  of  material,  and  how  much  to  in- 
creasing pressure,  and  how  much  these  are  coun- 
terbalanced by  expansion  due  to  increasing  heat, 
it  is  impossible  to  determine. 

The  increase   of  density  has  been  somewhat 

,     J  .,,          . .      ,  ,  FIG.  130.— Diagram  illustrat- 

arbitranly  assumed  to  follow  an  arithmetical  law.  ing  the  increasing  Dengi- 
Under  this  condition  a  density  equal  to  the  mean 

density  would  be  found  at  J  radius  from  the  surface,  and  taking  the 
surface  density  at  2,  and  the  mean  density  at  5 -5,  the  central  density 
would  be  16.  In  the  diagram  (Fig.  130),  if  a  c  =  radius,  the  ordinate 
ax  —  surface  density  =  2,  and  I  y  =  mean  density  =  5'5,  then  c  z, 
the  central  density,  will  be  =  16. 

It  is  needless  to  say  that  this  result  (Plana's)  is  unreliable. 


166 


GENERAL   FORM   AND   STRUCTURE   OF  THE  EARTH. 


3.— The  Crust  of  the  Earth. 

The  surface  of  the  earth  undoubtedly  differs  greatly  in  many  re- 
spects from  its  interior,  and  therefore  the  exterior  portion  may  very 
properly  be  termed  a  crust.  It  is  a  cool  crust,  covering  an  incandescent 
interior ;  a  stratified  crust,  covering  an  unstratified  interior ;  probably 
an  oxidized  crust,  covering  an  unoxidized  interior ;  and  many  suppose 
a  solid  crust,  covering  a  liquid  interior.  This  last  idea,  although 
very  doubtful  (p.  79),  has  probably  given  rise  to  the  term  crust.  The 
term,  however,  is  used  by  all  geologists,  without  reference  to  any  the- 
ory of  interior  condition,  and  only  to  express  that  portion  of  the  ex- 
terior which  is  subject  to  human  observation.  The  thickness  which  is 
exposed  to  inspection  is  about  ten  to  twenty  miles. 

Means  of  Geological  Observation. — The  means  by  which  we  are 
enabled  to  inspect  the  earth  below  its  immediate  surface  are  :  1.  Arti- 
ficial sections,  such  as  mines,  artesian  wells,  etc.  These,  however,  do 
not  penetrate  below  the  insignificant  depth  of  half  a  mile.  2.  Natural 
sections ',  such  as  cliffs,  ravines,  canons,  etc.  These,  as  we  have  already 
seen  (p.  17),  sometimes  penetrate  5,000  to  6,000  feet.  3.  Folding,  and 
subsequent  erosion  of  the  crust,  by  which  strata  from  great  depths  have 
their  edges  exposed.  Thus,  in  passing  along  the  surface  from  s  to  a  (Fig. 


FIG.  181. 

131),  lower  and  lower  rocks  are  successively  brought  under  inspection. 
The  dotted  lines  show  how  much  has  been  cut  away,  and  therefore  the 
depth  of  strata  exposed.  In  this  way  often  ten  miles  depth  of  strata  are 
brought  into  view.  This  is  by  far  the  most  important  means  of  ob- 
servation ;  without  it  the  study  of  geology  would  be  almost  impossible. 
4.  Volcanoes  bring  up  to  the  surface  materials  from  unknown  but 
probably  very  great  depths. 

Ten  miles  seems  an  insignificant  fraction  of  the  earth's  radius,  being 
in  fact  equivalent  to  less  than  one  thirtieth  of  an  inch  in  a  globe  two 
feet  in  diameter.  It  may  seem  at  first  sight  an  insufficient  basis  for  a 
science  of  the  earth.  We  must  recollect,  however,  that  only  this  crust 
has  been  inh^ited  by  animals  and  plants — on  this  crust  only  have 


GENERAL   SURFACE   CONFIGURATION   OF  THE   EARTH.  167 

operated  atmospheric,  aqueous,  and  organic  agencies — and  therefore 
on  this  insignificant  crust  have  been  recorded  all  the  most  important 
events  in  the  history  of  the  earth. 

4.  General  Surface  Configuration  of  the  Earth. 

The  surface  inequalities  of  the  earth  are  of  two  general  kinds, 
which  may  be  called  greater  and  lesser.  The  one  is  due  to  interior, 
the  other  to  exterior  causes ;  the  one  to  igneous,  the  other  to  aqueous 
or  erosive  agencies.  The  lesser  inequalities  we  will  treat  under  the 
head  of  forms  of  sculpture  (p.  '260).  Our  discussion  now  is  limited 
to  the  greater.  Again,  these  are  of  two  orders  of  greatness,  viz.,  those 
which  constitute  land-masses  and  ocean  basins,  and  those  which  con- 
stitute mountain-ranges  and  intervening  valleys.  These  latter  we 
shall  treat  fully  hereafter  (p.  250) ;  we  are  therefore  specially  con- 
cerned now  with  the  former. 

Nearly  three  quarters  of  the  whole  surface  of  the  earth  is  covered  by 
the  ocean.  The  mean  height  of  the  continents,  according  to  the  most 
recent  results,  is  as  follows :  Europe,  984  feet ;  Asia  and  Africa,  1,640  feet ; 
America,  North  and  South,  1,083  feet ;  Australia,  820  feet.  The  mean 
height  of  all  land  is  given  as  about  1,378  feet.*  These  figures  are  con- 
siderably greater  than  those  given  by  Humboldt  and  heretofore  adopted. 

The  mean  depth  of  the  ocean  is  probably  12,000  to  15,000  feet 
(Thompson).  There  is  probably  water  enough  in  the  ocean,  if  the 
inequalities  of  the  earth's  surface  were  removed,  to  cover  the  earth  to 
a  depth  of  about  two  miles. 

The  extreme  height  of  the  land  above  the  sea-level  is  five  miles, 
and  the  extreme  depth  of  the  ocean  is  at  least  as  much.  The  extreme 
relief  of  the  solid  earth  is  therefore  not  less  than  ten  miles. 

Cause  of  Land-Surfaces  and  Sea-Bottoms.— The  most  usual  idea 
among  geologists  as  to  the  general  constitution  of  the,,earth  is  that  the 
earth  is  still  essentially  a  liquid  mass,  covered  by  a  solid  shell  of  twen- 
ty-five to  thirty  miles  in  thickness ;  and  that  the  great  inequalities, 
constituting  land-surfaces  and  ocean-bottoms,  are  produced  by  the 
upbending  and  down-bending  of  this  crust  into  convex  and  concave 
arches,  as  shown  in  Fig.  132.  The  clear  statement  of  this  view  is 
sufficient  to  refute 
it ;  for,  when  it  is 
remembered  that 

the    arches    with  FlG  132 

which  we  are  here 

dealing  have  a  span  of  nearly  a  semi-circumference  of  the  earth,  it 
becomes  evident  that  no  such  arch,  either  above  or  below  the  mean 

*Krummcl,  American  Naturalist,  vol.  xiii,  p.  464,  1879,' 


168      GENERAL  FORM  AND  STRUCTURE  OF  THE  EARTH. 

level,  could  sustain  -itself  for  a  moment.  The  only  condition  under 
which  such  inequalities  could  sustain  themselves  on  a  supporting  liquid 

is  the  existence 
of  inequalities  on 
the  under  surface 
of  the  crust  next 

FIG.  133.— Diagram  illustrating  the  Conditions  of  Equilibrium  of  a  Solid  +i,0    li'rmirl      aimi 
Crust  on  a  Liquid  Interior.  liquid,    Sir 

lar  to  those  on 

the  upper  surface,  but  in  reverse,  as  shown  in  Fig.  133.  And  these 
lower  or  under-surface  inequalities  would  have  to  be  repeated  not  only 
for  the  largest  inequalities,  viz.,  continental  surfaces  and  ocean-bottoms, 
but  also  for  great  mountain  plateaus.  And  thus  the  hypothesis  seems 
to  break  down  with  the  weight  of  its  own  assumption.* 

Besides,  we  have  already  given  good  reasons  (pages  85-87)  for  be- 
lieving that  the  earth  is  substantially  solid.  Upon  the  hypothesis  of  a 
substantially  solid  earth,  we  explain  the  great  inequalities  constituting 
continental  surfaces  and  ocean-bottoms  by  unequal  radial  contraction 
of  the  earth  in  its  secular  cooling. 

The  earth  was  undoubtedly  at  one  time  an  incandescent  liquid 
globe.  It  then,  as  we  believe,  cooled  to  a  substantial  solid,  although 
probably  with  a  sub-crust  layer  underlying  large  areas  of  the  solid 
crust,  and  separating  it  from  the  solid  nucleus.  When  first  solidified 
the  earth  was  doubtless  a  regular  oblate  spheroid,  and,  when  sufficiently 
cool  to  allow  condensation  of  aqueous  vapor,  covered  with  a  universal 
ocean.  By  continued  cooling  it  gradually  contracted,  and  if  the  rate 
of  cooling  and  contraction  had  been  equal  in  all  parts  of  the  surface 
it  would  have  retained  its  regular  spheroid  form.  But,  without  perfect 
homogeneity  of  composition  and  equality  of  conductivity  and  of  co- 
efficient of  contraction  in  all  parts  (which  is  extremely  improbable), 
such  equality  of  cooling  and  contraction  would  be  impossible.  Some 
parts,  therefore,  cooled  and  contracted  toward  the  center  more  rapidly 
than  others.  These  more  rapidly  contracting  areas  would  form  hollows 
and  the  less  rapidly  contracting  areas  protuberances.  The  waters  would 
be  gathered  in  the  hollows  and  form  oceans,  while  the  protuberances 
would  become  continents.  In  other  words,  oceanic  basin  and  land- 
masses  are  the  result  of  slight  distortion  of  the  regular  spheroid  by. un- 
equal radial  contraction.  This  is  evidently  a  true  cause ;  and,  when 
we  consider  the  smallness  of  these  inequalities  in  comparison  with  the 
size  of  the  earth,  it  will  seem  a  sufficient  cause.  The  mean  inequality  of 
the  kind  we  are  now  considering  is  about  two  and  a  half  miles.  This 

*  It  has  been  shown  by  G.  H.  Darwin  that  the  great  inequalities  of  the  earth's  sur- 
face could  not  be  sustained  unless  the  earth  be  as  rigid  as  granite  for  a  depth  of  1,000 
miles. — Proceedings  of  the  Royal  Society,  June,  1881. 


GENERAL  SURFACE  CONFIGURATION  OF  THE  EARTH. 


169 


in  a  globe  of  two  feet  in  diameter  would  be  less  than  one  one-hundredth 
of  an  inch — an  amount  that  would  be  scarcely  perceptible.  If  a 
globe  of  clay  or  of  stone  of  this  size  were  heated  to  incandescence  and 
in  this  condition  ground  to  a  true  sphere  and  then  allowed  to  cool,  it 
is  probable  that  the  inequality  would  be  as  great  as  or  greater  than  the 
above.* 

It  is  only  the  greatest  inequalities,  viz.,  land-surfaces  and  sea-bot- 
toms, which  we  account  fo/in  this  way.  Mountain-chains  are  certainly 
formed  by  a  different  process,  which  we  will  discuss  under  that  head 
(p.  250) ;  and  it  is  even  possible  that  the  causes  which  operate  to 
produce  mountain-chains  may  also  produce  these  greatest  inequalities. 

The  continuance  of  these  causes  would  tend  constantly  to  increase 
the  extent  and  height  of  the  land,  and  to  increase  the  depth,  but  dimin- 
ish the  extent  of  the  sea.  This,  on  the  whole,  seems  to  have  been  the 
fact,  during  the  history  of  the  earth,  as  will  be  shown  in  Part  III. 
Nevertheless,  local  causes,  both  aqueous  and  igneous,  as  already  shown 
in  Part  I,  have  greatly  modified  the  general  contour,  both  map  and 
profile,  given  by  secular  contraction* 

Laws  of  Continental  Form. — That  the  general  contour  of  continents 
and  sea-bottoms  has  been  determined  by  some  general  cause,  such  as 
secular  contraction,  affecting  the  whole  earth,  is  further  shown  by  the 
laws  of  continental  form.  The  most  important  of  these  are  as  follows : 

1.  Continents  consist  of  a  great  interior  basin,  bordered  by  elevated 
coast-chain  rims.  This  typical  form  is  most  conspicuously  seen  in 
North  and  South  America,  Africa,  and  Australia.  Europe-Asia  is 
more  irregular,  and  therefore  the  typical  form  is  less  distinct.  We 
give  in  Fig.  134,  A  and  B,  an  east-and-west  section  of  North  America 
and  of  Australia,  as  typical  examples  of  continental  structure. 


FIG.  134.—^!,  Section  across  North  America;  B,  Section  across  Australia  (after  Guyot). 

The  great  rivers  of  the  world,  e.  g.,  the  Nile,  Mississippi,  Amazon, 
La  Plata,  etc.,  drain  these  interior  continental'basins. 

*  To  this,  according  to  Faye  (Comptes  Rendus,  vol.  xc,  p.  1185, 1880),  must  be  added 
still  another  cause.  As  soon  as  the  water  collects  in  the  depressions  formed  by  un- 
equal radial  contraction,  its  very  presence  would  tend  to  increase  the  cooling  and  con- 
tracting of  these  parts,  and  thus  to  deepen  still  further  the  depressions.  This  effect 
results  (1)  from  the  greater  conductivity  of  water  as  compared  with  rock,  and  (2)  from 
the  circulation  of  ice-cold  water  from  the  poles  along  the  sea-bottom  (p.  40). 


170      GENERAL  FORM  AND  STRUCTURE  OF  THE  EARTH. 

2.  In  each  continent  the  greatest  range  of   mountains  faces  the 
greatest  ocean.     Thus  in  America  the  greatest  range  is  on  the  west, 
facing  the  Pacific ;  while  in  Africa  the  greatest  range  is  on  the  east, 
facing   the  Indian  Ocean.      In  Asia  the  Himalayas  face  the  Indian 
Ocean,  while  the  Altai  face  the  Polar  Sea.     In  Australia  the  greatest 
range  is  to  the  east,  facing  the  Pacific. 

3.  The  greatest  ranges  have  been  subjected   to  the  greatest  and 
most  complex  foldings  of  the  strata,  and  are  the  seats  of  the  greatest 
metamorphism  (p.  221)  and  the  greatest  volcanic  activity. 

4.  The  outlines  of  the  present  continents  have  been  sketched  in  the 
earliest  geological  times,  and  have  been  gradually  developed  and  per- 
fected in  the  course  of  the  history  of  the  earth.     In  the  case  of  the 
North  American  Continent  this  will  be  shown  in  Part  III. 

The  cause  of  some  of  these  laws  will  be  discussed  under  the  head 
of  Mountain- Chains. 

Rocks. 

In  geology  the  term  rock  is  used  to  signify  any  material  consti- 
tuting a  portion  of  the  earth,  whether  hard  or  soft.  Thus,  a  bed  of 
sand  or  clay  is  no  less  a  rock  than  the  hardest  granite.  In  fact,  it  is 
impossible  to  draw  any  scientific  distinction  between  materials  founded 
upon  hardness  alone.  The  same  mass  of  limestone  may  be  soft  chalk 
in  one  part  and  hard  marble  in  another :  the  same  bed  of  clay  may  be 
hard  slate  in  one  part  and  good  brick-earth  in  another ;  the  same  bed 
of  sandstone  may  be  hard  gritstone  in  one  part  and  soft  enough  to  be 
spaded  in  another.  The  same  volcanic  material  may  be  stony,  glassy, 
scoriaceous,  or  loose  sand  or  ashes. 

Classes  of  Rocks. — All  rocks  are  divided  into  two  great  classes,  viz., 
stratified  rocks  and  unstratified  rocks.  Stratified  rocks  are  more  or 
less  consolidated  sediments,  and  are  usually,  therefore,  more  or  less 
earthy  in  structure  and  of  aqueous  origin.  Unstratified  rocks  have 
been  more  or  less  completely  fused,  and  therefore  are  crystalline  in 
structure  and  of  igneous  origin. 


CHAPTER  II. 

STRATIFIED    OR  SEDIMENTARY  ROCKS. 

SECTION  1. — STRUCTURE  AKD  POSITION. 

Stratification. — Stratified  rocks  are  characterized  by  the  fact  that 
they  are  separated  by  parallel  division-planes  into  larger  sheet-like 
masses  called  strata,  and  these  into  smaller  layers  or  beds,  and  these 


STRUCTURE  AND  POSITION. 


171 


xh. 


again  into  still  smaller  lamina.  These  terms  are  purely  relative,  and 
are  therefore  somewhat  loosely  used.  Usually,  however,  the  term 
stratum  refers  to  the  mineralogical  character ;  the  term  layer  to  sub- 
divisions of  a  stratum  distinguishable  by  difference  of  color  or  fine- 
ness ;  and  the  term  lamina  to 
those  smallest  subdivisions,  evi- 
dently produced  by  the  sorting 
power  of  water.  For  instance,  in 
the  annexed  figure  we  have  three 
strata  of  sandstone,  clay,  and 
limestone,  each  divisible  into  two 
layers  differing  in  fineness  or  com- 
pactness of  the  material,  and  all 
finely  laminated  by  the  sorting 
power  of  water.  The  lamination, 

however,   is   not    represented,    ex-  FIG.  135.— Sections  of  horizontal  and  inclined  strata: 
,  7         «,  soil;  ss,  sandstone;  sh,  shale;  Ls,  limestone. 

cept    in    the    clay    stratum,    sh. 

There  is  another  structure  represented  in  the  figure — viz.,  the  cross 
fractures  or  joints.  These,  however,  are  not  peculiar  to  stratified  rocks, 
and  will  be  discussed  at  another  time. 

Extent  and  Thickness. — Probably  nine-tenths  of  the  surface  of  the 
land,  and,  of  course,  the  whole  of  the  sea-bottom,  are  covered  with 
stratified  rocks.  Even  where  these  are  wanting  it  is  because  they 
have  been  removed  by  erosion  or  else  covered  up  and  concealed  by 
fused  matter  outpoured  on  the  surface.  This  proves  that  every  portion 
of  the  surface  of  the  earth  has  been  at  some  time  covered  with  water. 
The  extreme  thickness  of  stratified  rocks  is  certainly  not  less  than 
twenty  miles ;  the  average  thickness  is  probably  several  miles. 

Kinds  of  Stratified  Rocks. — Stratified  rocks  are  of  three  kinds,  and 
their  mixtures,  viz.,  arenaceous  or  sand  rocks,  argillaceous  or  clay 
rocks,  and  calcareous  or  lime  rocks.  Arenaceous  rocks,  in  their  inco- 
herent state,  are  sand,  gravel,  shingle,  rubble,  etc.,  and  in  their  com- 
pacted state  are  sandstones,  gritstones,  conglomerates,  and  breccias. 
Conglomerates  are  composed  of  rounded  pebbles,  and  breccias  of  angu- 
lar fragments  cemented  together.  Argillaceous  rocks,  in  their  inco- 
herent state,  are  muds  and  clays;  partially  consolidated  and  finely 
laminated  they  form  shales,  and  thoroughly  consolidated  they  form 
slates.  Calcareous  rocks  are  chalk,  limestone,  and  marble.  They  are 
seldom  in  an  incoherent  state,  except  as  chalk. 

These  different  kinds  of  rocks  graduate  into  each  other  through 
intermediate  shades.  Thus  we  may  have  argillaceous  sandstones,  cal- 
careous sandstones,  and  calcareous  shales  or  marls. 

The  most  important  points  connected  with  stratified  rocks  we  will 
now,  for  the  sake  of  greater  clearness,  bring  out  in  the  form  of  distinct 


172  STRATIFIED   OR  SEDIMENTARY   ROCKS. 

propositions.     On  these  propositions  is  based  nearly  the  whole  of  geo- 
logical reasoning. 

I.  Stratified  Rocks  are  more  or  less  Consolidated  Sediments. — The 
evidence  of  this  fundamental  proposition  is  abundant  and  conclusive. 
1.  Beds  of  mud,  clay,  or  sand,  as  already  stated,  may  often  be  traced 
by  insensible  gradations  into  shales  and  sandstones.  2.  In  many  places 
the  process  of  consolidation  is  now  going  on  before  our  eyes.  This  is 
most  conspicuous  in  sediments  deposited  at  the  mouths  of  large  rivers 
whose  waters  contain  abundance  of  carbonate  of  lime  in  solution,  or  on 
the  coasts  of  seas  containing  much  carbonate  of  lime.  Thus  the  sedi- 
ments of  the  Rhine  are  now  consolidating  into  hard  stone  (p.  82),  and 
on  the  coasts  of  Florida,  Cuba,  and  on  coral  coasts  generally,  com- 
minuted shells  and  corals  are  quickly  cemented  into  solid  rock  (p.  156). 
3.  All  kinds  of  lamination  produced  by  the  sorting  power  of  water 
which  have  been  observed  in  sediments,  have  also  been  observed  in 
stratified  rocks.  4.  Stratified  rocks  contain  the  remains  of  animals  and 
plants,  precisely  as  the  stratified  mud  of  our  present  rivers  contains 
river-shells,  our  present  beaches  sea-shells,  or  the  mud  of  our  swamps 
the  bones  of  our  higher  animals  drifted  from  the  high  lands.  5.  Im- 
pressions of  various  kinds,  such  as  ripple-marks,  rain-prints,  footprints, 
etc.,  evidently  formed  when  the  rock  was  in  the  condition  of  soft  mud, 
complete  the  proof.  It  may  be  considered  as  absolutely  certain  that 
stratified  rocks  are  sediments.  Arenaceous  and  argillaceous  rocks  are 
the  debris  of  eroded  land,  and  are  therefpre  called  mechanical  sedi- 
ments or  fragmented  rocks.  Limestones  are  either  chemical  deposits 
in  lakes  and  seas,  or  are  the  comminuted  remains  of  organisms.  They 
are  therefore  either  chemical  or  organic  sediments.  Conglomerates, 
grits,  and  sandstones,  indicate  violent  action ;  shales  and  clays  quiet 
action  in  sheltered  spots.  Limestones  are  sometimes  produced  by  vio- 
lent action — e.  g.,  coral  breccia — sometimes  very  quiet  action,  as  in 
deep-sea  deposits. 

We  have  already  seen  (p.  4)  that  rocks  under  atmospheric  agen- 
cies are  disintegrated  into  soils,  and  these  soils  are  carried  by  rivers 
and  deposited  as  sediments  in  lakes  and  seas.  Now  we  see  that  these 
sediments  are  again  in  the  course  of  time  consolidated  into  rocks,  to  be 
again  raised  by  igneous  agencies  into  land,  and  again  disintegrated  into 
soils,  and  redeposited  as  sediments.  Thus  the  same  material  has  been 
in  some  cases  worked  over  many  times  in  an  ever-recurring  cycle. 
This  is  another  illustration  of  the  great  law  of  circulation,  so  universal 
in  Nature. 

Cause  of  Consolidation. — The  consolidation  of  sediments  into  rocks 
in  many  cases  is  due  to  some  cementing  principle,  such  as  carbonate  of 
lime,  silica,  or  oxide  of  iron,  present  in  percolating  waters.  In  such 
cases  the  consolidation  often  takes  place  rapidly.  In  other  cases  it  is 


STRUCTURE   AND   POSITION. 


173 


due  to  long-continued  heavy  pressure,  and  in  still  others  to  long-con- 
tinued, though  not  necessarily  very  great,  elevation  of  temperature  in 
presence  of  water.  In  these  cases  the  process  is  very  slow,  and  there- 
fore it  has  not  progressed  greatly  in  the  more  recent  rocks. 

II.  Stratified  Rocks  have  been  gradually  deposited.— The  following 
facts  show  that  in  many  cases  rocks  have  been  deposited  with  extreme 
slowness :  1.  Shales  are  often  found  the  lamination  of  which  is  beau- 
tifully distinct  and  yet  each  lamina  no  thicker  than  cardboard.  Now, 
each  lamina  was  separately  formed  by  alternating  conditions,  such  as 
the  rise  and  fall  of  tide,  or  the  flood  and  fall  of  river.  2.  Again,  on  the 
interior  of  imbedded  shells  of  mollusca,  or  on  the  outer  surface  of  the 
shells  of  sea-urchins  deprived  of  their  spines, 
are  often  found  attached  other  shells,  as 
shown  in  the  following  figures.  Now,  these 
shells  must  have  been  dead,  hut  not  yet  cov- 
ered with  deposit  during  the  whole  time  the 
attached  shell  was  growing.  As  a  general 
rule,  in  fragmental  rocks  the  finest  materials, 
such  as  clay  and  mud,  have  been  deposited 


FIG.  136.— Serpula  on  Shell  of  an  Echinoderm. 


FIG.  137.— Serpulae  on  Interior 
of  a  Shell. 


very  slowly,  while  coarse  materials,  such  as  sand,  gravel,  and  pebbles, 
have  been  deposited  rapidly.  Limestones,  being  generally  formed  by 
the  accumulation  of  the  calcareous  remains  of  successive '  generations 
of  organisms,  living  and  dying  on  the  same  spot,  must  have  accumu- 
lated with  extreme  slowness.  The  same  is  true  of  infusorial  earths. 

It  is  necessary,  therefore,  to  bear  in  mind  that  all  stratified  rocks 
were  formed  in  previous  epochs  by  the  regular  operation  of  agents 
similar  to  those  in  operation  at  present,  and  not  by  irregular  or  cataclys- 
mic action,  as  supposed  by  the  older  geologists.  Thus,  cceteris  paribus, 
the  thickness  of  a  rock  may  be  taken  as  a  rude  measure  of  the  time 
consumed  in  its  formation. 

III.  Stratified  Rocks  were  originally  nearly  horizontal. — The  hori- 
zontal position  is  naturally  assumed  by  all  sediments  in  obedience  to 
the  law  of  gravity.  When,  therefore,  we  find  strata  highly  inclined  or 
folded,  we  conclude  that  their  position  has  been  subsequently  changed. 
It  must  not  be  supposed,  however,  that  the  planes  which  separate  strata 
were  originally  perfectly  horizontal,  or  that  the  strata  themselves  were 


174 


STRATIFIED   OR  SEDIMENTARY   ROCKS 


of  unvarying  thickness,  and  laid  atop  of  each  other  like  the  sheets  of  a 
ream  of  paper.  On  the  contrary,  each  stratum,  when  first  deposited, 
must  be  regarded  as  a  widely-expanded  cake,  thickest  in  the  middle  and 
thinning  out  at  the  edges,  and  interlapping  there  with  other  similar 
cakes.  Fig.  138  is  a  diagram  showing  the  mode  of  interlapping.  The 


FIG.  138.— Diagram  showing  Thinning  out  of  Beds:  a,  sandstones  and  conglomerates;  b,  limestones. 

extent  of  these  cakes  depends  upon  the  nature  of  the  material.  In  fine 
materials  strata  assume  the  form  of  extensive  thin  sheets,  while  coarse 
materials  thin  out  more  rapidly,  and  are  therefore  more  local. 

The  most  important  apparent  exception  to  the  law  of  original  hori- 
zontality  is  the  phenomenon  of  oblique  or  cross  lamination.    This  kind 

of  lamination  is  formed  by  rapid,  shift- 
ing currents,  bearing  abundance  of 
coarse  materials,  or  by  chafing  of  waves 
on  an  exposed  beach.  Many  examples 
of  similar  lamination  are  found  in 
rocks  of  previous  epochs.  Figs.  139 
FIG.  m-obiique  Lamination.  and  14°  represent  such  examples.  In 

some  cases  oblique  lamination  may  be 

mistaken  for  highly-inclined  strata ;  careful  examination,  however,  will 
show  that  the  strata  are  not  parallel  with  the  laminae.  The  strata  were 


FIG.  140.— Section  on  Mississippi  Central  Railroad  at  Oxford  (after  Hilgard):  Oblique  Lamination. 

originally  (and  in  the  cases  represented  in  the  figures  are  still)  hori- 
zontal, while  the  laminae  are  oblique. 

Elevated,  Inclined,  and  Folded  Strata. — We  may  assume  with  con- 
fidence that  stratified  rocks  were  deposited  as  sediments  at  the  bottom 
of  water  and  in  a  horizontal  or  nearly  horizontal  position.  But  we  do  not 
now  find  them  usually  in  this  condition,  place,  or  position.  Sometimes, 
indeed,  they  are  still  soft,  but  usually  stony ;  sometimes  in  the  vicinity 


STRUCTURE   AND   POSITION. 


175 


of  water,  but  oftener  far  in  the  interior  of  continents  and  high  up  the 
slopes  of  mountains ;  sometimes  they  are  still  horizontal  though  ele- 


Fio.  141. 


vated  (Fig.  141) ;  but  often,  especially  in  mountain-regions,  we  find  them 
tilted  at  all  angles,  folded,  contorted  (Fig.  142)  overturned,  broken, 

r~A 


FIG.  142.— Contorted  Strata. 


and  slipped,  so  that  it  is  difficult  sometimes  to  determine  their  original 
order  of  superposition.  Again,  in  folded  strata,  sometimes  we  have  the 
most  intricate  crumplings  of  the  finer  lamina,  such  as  may  be  seen  in  a 
hand  specimen  (Fig.  143).  Sometimes  whole  groups  of  strata  are  thus 


FIG.  143.— Crumpled  Laminae  (after  Geikie). 


folded,  as  can  be  seen  at  one  view  on  a  sea-cliff  or  canon  wall  (Fig.  144). 
Sometimes  the  whole  crust  of  the  earth,  for  miles  in  thickness  and 
many  miles  in  extent,  are  thrown  into  great  crust- waves  constituting 
mountain-ranges  with  their  •  intervening  valleys  (Figs.  145  and  146). 


176 


STRATIFIED   OR  SEDIMENTARY   ROCKS. 


In  such  cases  the  folded  structure  is  not  visible  at  one  view,  but  only 
brought  out  by  extended  survey.     In  cases  of  strong  folding  the  strata 


FIG.  144. — Contorted  Strata  (from  Logan). 

are  often  broken  and  dislocated  (Figs.  196,  197,  etc.).     In  all  cases  of 
elevated  strata,  whether  level  or  tilted  and  folded,  large  portions  of  the 


FIG.  145.— Section  of  Appalachian  Chain. 


upper  parts  are  carried  away  by  erosion  and  the  remainder  is  left  in 
isolated  patches  and  basins,  or  else  standing  at  all  angles,  with  their 


FIG.  146.— Section  of  the  Jura  Mountains. 


edges  exposed  (Figs.  144,  145,  and  in  all  the  other  figures).     Such  ex- 
posure on  the  surface  of  the  edges  of  eroded  strata  is  called  an  outcrop. 


\  d 

\  \  \  \ 

FIG.  147.— Upturned  and  Eroded  Strata,  Elk  Mountains,  Colorado  (after  Hayden). 

Definition  of  Terms. — There  are  certain  terms  in  frequent  use  by 
geologists  which  must  now  be  defined.  These  are  dip  and  strike,  anti- 
cline and  syncline  and  conformity  and  unconformity. 

Dip  anjd  Strike. — The  dip  of  strata  is  their  inclination  to  a  hori- 
zontal plane.  Thus  in  Fig.  148  the  strata  dip  southward  about  30°. 
The  angle  of  dip  is  measured  by  a  clinometer  (Fig.  149),  and  the  cttrec- 


cttrec- 


STRUCTURE  AND   POSITION. 


177 


tion  of  dip  by  a  compass.  These  two  are  often  conveniently  united  in 
one  instrument.  As  thus  determined  the  angle  of  dip  varies  from 
0°  to  90°,  or  from  horizon- 

tality  to  verticality.      Fig.    sr      a  "5    >S 

150  is  an  example  of  verti- 
cal strata.  In  strongly 
folded  rocks  the  strata 
may  be  pushed  beyond  the 
perpendicular  (Fig  151), 

or    even     completely     re-  FIG.  143. 

versed  (Fig.  205(7),  so  that 
the  change  from  the  original  position  may  be  nearly  or  quite  180°. 

In  a  series  of  regularly  dipping  strata,  like  that  of  Fig.  148,  it  is  easy 
to  estimate  the  thickness  of  the  series.     The  thickness,  b  c,  =  distance-1 


FIG.  149.— Clinometer. 

a  b  X  sin.  of  the  angle  of  dip  30°.  We  sometimes  find  an  actual  sec- 
tion such  as  that  represented  in  the  figure,  but  more  .usually  we  observe 
the  successive  outcrops  on 
the  surface  and  the  angle 
of  dip,  and  construct  an 
ideal  section.  This  is  easy 
enough  if  the  rocks  are 
bare,  but  if  covered  with 
soil,  we  must  take  advan- 
tage of  every  bare  spot,  of 
every  ravine,  gully,  and 
stream  -  bed  where,  the 
rocks  may  be  exposed,  of 
every  quarry,  railroad-cut- 
ting, well,  etc.,  and  put  these  together  in  the  attempt  to  make  a  map  of 
outcrop  and  a  section. 

The  strike  of  strata  is  the  direction  of  their  trend,  or,  more  accu- 
rately, is  the  line  of  intersection  of  the  strata  with  a  horizontal  plane. 
It  is  always  at  right  angles  to  the  line  of  dip.  If  the  dip  is  north  or 
south,  the  strike  is  east  and  west.  If  the  strata  are  plane,  the  strike  is 
a  straight  line ;  but  if  they  are  bent,  the  strike  may  be  a  curve.  For 
12 


FIG.  150.— Vertical  Strata. 


178 


STRATIFIED   OR   SEDIMENTARY  ROCKS. 


FIG.  151. 


example,  if  the  strata  are  lifted  up  in  the  form  of  a  cone  or  a  dome, , 
the  strike  will  be  circular  ;  if  the  strata  be  folded  and  then  tilted  in  a 

direction  at  right  an- 
gles to  the  folding 
force,  the  strike  will 
be  sinuous.  Again, 
if  the  surface  of  the 
ground  is  level,  the 
outcrop  will  be  the 
strike,  and  will  be  straight  or  sinuous,  according  as  the  strike  is  one  or 
the  other.  But  the  outcrop  is  usually  far  more  irregular  than  the 
strike,  as  it  is  affected  also  by  irregularities  of  surface  produced  by 
erosion ;  so  that  in  a  broken  country  the  outcrop  of  folded  strata  is  ex- 
tremely complex.  •  .-. 

Anticline  and  Syncline. — Strata  are  usually  more  or  less  folded,  and 
therefore  form  alternate  saddles  and  troughs.  The  saddles  are  anticlines, 
the  troughs  synclines.  The  line  along  the  top  of  the  saddle  is  an  anti- 
clinal axis,  the  line  along  the  bottom  of  the  trough  a  synclinal  axis. 
If  it  were  not  for  erosion,  the  anticlines  would  be  ridges  and  the  syn- 
clines valleys.  If  erosion  cuts  down  to  nearly  a  plane,  as  in  Fig.  152, 
then  an  anticline  is 
known  by  the  strata 
being  repeated  on 
each  side  of  an  axis 
and  dipping  away 
from  one  another  ;  a 
syncline  by  the  strata 
also  repeated  on  each  side  of  an  axis  but  dipping  toward  one  another. 
In  the  one  case  the  oldest  and  lowest  strata  are  on  the  axis  and  they 
become  higher  and  newer  as  we  go  either  way ;  in  the  other  the  upper- 
most and  newest  strata  are  along  the  axis,  and  they  become  lower  and 
older  as  we  go  either  way. 

But  erosion  usually  forms  ridges  and  valleys.     In  this  case  some- 
times the  ridges  are  anticlines 

/-;>:::.:::.::::;;;;-":;;x.  B  and  the  valleys  synclines,   as 

in  Fig.  153,  but  sometimes  the 
reverse  is  true.  It  is  very 
common  to  have  synclinal 

FIG.  153.-Section  of  Undulating  Strata.  ridgGS    aTld    anticlinal    Valleys 

(Fig.  154).     In  this  case  the 

original  configuration  is  completely  reversed  by  erosion.     This  will  be 
explained  in  another  chapter  (p.  268). 

Fig.  153  and  the  following  figures  (155  and  156)  will  illustrate  some 
of  these  points.     Suppose  we  have  strata  gently  folded,  so  as  to  make 


FIG.  152. 


STRUCTURE   AND   POSITION. 


179 


FIG.  154. 


an  anticline  and  syncline,  and  then  the  whole  tilted  and  finally  eroded 
down  to  a  nearly  level  surface.  The  map  of  the  outcrop  of  such  a 
series  is  shown  in  Fig.  155, 
in  which  A  A'  is  an  anti- 
cline and  B  B'  a  syncline, 
and  the  arrows  show  the 
dip  on  either  side  of  the 
axes  and  also  the  general 
dip  of  the  whole  northward. 
Fig.  153  is  a  section  of  the  same.  The  sinuosity  of  the  outcrop  is,  of 
course,  the  necessary  result  of  the  folding  and  tilting.  We  have  sup- 
posed the  strata  folded  and 
tilted,  and  then  showed 
what  the  outcrop  would  be. 
The  field  geologist,  of 
course,  follows  the  reverse 
method  :  he  works  out  the 
outcrop,  and  infers  the 
structure  and  position  of 
strata.  If  the  strata  had 
been  simply  folded  but  not 
tilted,  then  the  outcrop  of 
the  same  section  (Fig.  153) 
would  be  much  simpler,  i.  e.,  in  parallel  lines  as  in  Fig.  156. 

The  cases  represented  by  these  figures  are  comparatively  simple,  and 
we  have  supposed  the  soil 
removed,  so  that  the  out- 
crop is  easily  traced.  But 
when  we  remember — 1. 
The  great  complexity  of 
the  outcrop  often  produced 
by  folding  and  tilting;  2. 
That  it  is  very  much  in- 
creased by  inequalities  of  erosion  ;  3.  That  it  is  still  further  increased 
by  fissuring  and  displacement ;  and,  worst  of  all,  4.  That  the  rocks  are 
largely  covered  by  soil — we  easily  see  the  difficulty  of  the  task  of  mak- 
ing a  good  geological  map  and  section  of  any  region. 

Conformity  and  Unconformity. — We  have  just  seen  that  all  land- 
surfaces  are  deeply  eroded  and  the  strata  are  left  with  their  edges  ex- 
posed. We  have  also  seen  (pp.  133-137)  that  the  crust  of  the  earth  is 
everywhere  in  a  state  of  slow  movement :  in  some  places  sea-bottoms 
are  rising  and  becoming  land-surfaces,  in  others  land-surfaces  are  sink- 
ing to  become  sea-bottoms.  Now,  the  same  thing  has  taken  place  in 
earlier  geological  times.  Suppose,  then,  an  eroded  land-surface  with  the 


FIG.  155.-Plan  of  Undulating  Strata. 


FIG.  156. 


180 


STRATIFIED   OR   SEDIMENTARY   ROCKS. 


strata-edges  exposed,  to  sink  down  and  become  ocean-bottom,  and  re- 
ceive sediments  covering  the  strata-edges  and  filling  the  erosion-hol- 
lows, and  afterward  to  rise  again  and  be  submitted  to  the  inspection  of 
the  geologist ;  Fig.  157  represents  in  section  what  he  would  see.  They 

are  interpreted  as 
follows  :  In  A 
and  B  the  lower 
series  of  strata 
was  first  deposit- 
ed ;  then  the  sea- 
bottom  was  raised 
to  land  -  surface 
and  the  strata 
tilted  and  eroded ; 
then  it  went  down 
again  and  re- 
ceived the  upper 
series ;  and,  final- 
ly, was  raised  and 
inspected  by  the 
geologist.  In  C 
the  process  was 
the  same,  except 
that  the  first  se- 
ries of  strata  was  raised  without:  tilting.  In  D  the  second  series  of 
strata  was  also  tilted  in  the  second  raising.  Now  the  strata  of  each 
series  are  said  to  be  conformable  among  themselves,  but  the  two  series 
are  unconformable  with  one  another. 

Definition. — Therefore,  strata  are  said  to  be  conformable  when  they 
are  parallel,  continuous,  and  therefore  formed  under  the  same  condi- 
tions, and  are  unconformable  when  they  are  discontinuous,  and  formed 
under  different  conditions  ;  the  discontinuity  being  always  marked  by 
an  old  eroded  land-surface.  Unconformable  strata  are  usually  non- 
parallel,  and  this  is  often  made  a  part  of  the  definition ;  but  this  is  riot 
necessary.  In  Fig.  157,  C,  there  is  no  want  of  parallelism.  The  reason 
we  have  already  explained. 

A  section  like  any  one  of  the  foregoing — among  the  commonest  in 
geology — reveals  many  interesting  events  :  1.  A  long  period  of  quiet, 
during  which  sediments  of  the  first  series  were  deposited  continuously 
on  a  sea-bottom.  The  length  of  this  period  is  measured  by  the  thick- 
ness of  the  series.  2.  A  period  of  elevation,  during  which  the  sea- 
bottom  became  land-surface.  We  have  no  means  of  estimating  the 
length  of  this  period.  3.  A  long  period  during  which  the  land-surface 
became  deeply  eroded.  The  length  of  this  period  is  measured  by  the 


FIG.  157.— Some  Cases  of  Unconformity. 


STRUCTURE   AND  POSITION.  181 

amount  of  erosion.  4.  A  period  of  subsidence,  during  which  the  land- 
surface  became  sea-bottom  We  can  not  estimate  the  length  of  this. 
5.  A  long  period  of  quiet,  during  which  the  second  series  of  sediments 
was  continuously  deposited.  This  period  is  estimated  by  the  thickness 
of  the  sediments.  6.  Another  period  of  elevation  by  which  the  whole 
was  brought  into  view.  The  process  is  more  fully  explained  in  connec- 
tion with  a  concrete  example  on  page  294  of  Part  III. 

It  is  evident,  then,  that  every  case  of  unconformity  represents  a  gap 
in  the  geological  record  at  that  place  ;  for  the  geological  record  is  written 
on  strata,  and  unconformity  means  a  land-surface  period,  during  which 
there  was  erosion  instead  of  sedimentation,  record-destroying  instead  of 
record-making.  The  gap  may  be  filled  and  the  record  recovered  by 
sediments  formed  at  that  time  in  some  other  place.  This  is  usually 
the  case,  but  not  always.  The  loss  of  record  may  be  partly  by  erosion, 
but  mostly  because  not  written  at  that  place. 

Now,  such  unconformities  and  lost  records  are,  as  we  have  seen,  the 
result  of  crust  oscillations.  But  crust  oscillations  produce  necessarily 
changes  in  physical  geography,  and  therefore  changes  of  climate,  and 
therefore  also  changes  of  faunas  and  floras.  They  consequently  mark 
the  great  divisions  and  subdivisions  of  geological  history. 

Geological  Formations. — A  group  of  strata  conformable  throughout 
and  containing  continuous  record,  and  separated  from  other  con- 
formable groups  by  a  line  of  unconformity,  is  called  a  geological  for- 
mation. There  are,  however,  other  tests  of  a  formation,  by  which 
hereafter  we  will  complete  the  definition. 

Cleavage  Structure* 

"We  have  thus  far  spoken  only  of  the  original  and  universal  structure 
of  stratified  rocks,  together  with  the  tiltings,  foldings,  and  erosion,  to 
which  they  have  been  subjected.  There  is,  however,  often  found  in 
stratified  rocks  a  superinduced  structure  which  simulates,  and  is  often 
mistaken  for  stratification.  It  is  called  cleavage  structure,  or  (since  it 
is  usually  found  in  slates)  slaty  cleavage.  This  subject  has  recently 
attracted  much  attention,  and  is  an  admirable  example  of  the  successful 
application  of  physics  to  the  solution  of  problems  in  geology. 

Cleavage  may  be  defined  as  the  easy  splitting  of  any  substance  in 
planes  parallel  to  each  other.  Such  definite  splitting  may  result,  in 
different  cases,  from  entirely  different  causes.  For  example  («),  under 
the  influence  of  the  sorting  power  of  water,  sedimentary  materials  may 
be  so  arranged  as  to  give  rise  to  easy  splitting  along  the  planes  of  lami- 

*  This  structure  is  usually  treated  under  metamorphic  rocks,  as  a  kind  of  metamor- 
phism  ;  but  it  is  found  in  rocks  which  have  not  undergone  ordinary  metamorphic  changes, 
and  it  is  produced  by  an  entirely  different  cause. 


182 


STRATIFIED   OR  SEDIMENTARY   ROCKS. 


FIG.  158. — Cleavage-Planes  cutting  through  Strata. 


nation.  Many  rocks  may  be  thus  split  into  large  coarse  slabs  called 
flag-stones,  and  are  used  for  paving  streets,  or  even  sometimes  as  roof- 
ing-slates. This  may  be  called  flag-stone  cleavage,  or  lamination  cleav- 
age. Again  (#),  the  arrangement  of  the  ultimate  molecules  of  a  mineral 
under  the  influence  of  molecular  or  crystalline  forces  gives  rise  to  an 
exquisite  splitting  along  the  planes  parallel  to  the  fundamental  faces 
of  the  crystal.  This  is  called  crystalline  cleavage.  Again  (c),  the  ar- 
rangement of  the  wood-cells  under  the  influence  of  vital  forces  gives 
rise  to  easy  splitting  of  wood  in  the  direction  of  the  silver-grain.  This 
may  be  called  organic  cleavage. 

Now,  in  certain  slates  and  some  other  rocks  is  found  a  very  perfect 
cleavage  on  a  stupendous  scale.  Whole  mountains  of  strata,  may  be 
cleft  from  top  to  bottom  in  thin  slabs,  along  planes  parallel  to  each 
other.  The  planes  of  cleavage  seem  to  have  no  relation  to  the  strata, 
but  cut  through  them,  maintaining  their  parallelism,  however  the  strata 

may  vary  in  dip 
(Fig.  158).  Usually 
the  cleavage-planes 
are  highly  inclined, 
and  often  nearly 
perpendicular.  It 
is  from  the  cleaving  of  such  slates  that  roofing-slates,  ciphering-slates, 
and  blackboard-slates  are  made.  This  remarkable  structure  has  long 
excited  the  interest  of  geologists,  and  many  theories  have  been  proposed 
to  explain  it. 

On  cursory  examination  of  such  rocks,  the  first  impression  is,  that 
the  cleavage  is  but  a  very  perfect  example  of  flag-stone  or  lamination 
cleavage — that  the  cleavage-planes  are  in  fact  stratification-planes,  and 
that  we  have  here  an  admirable  example  of  finely  laminated  rocks 
which  have  been  highly  tilted  and  then  the  edges  exposed  by  erosion. 
Closer  examina- 
tion, however,  will 
generally  show  the 
falseness  of  this 
view.  Fig.  159 
represents  a  mass 
of  slate  in  which 
three  kinds  of 
structure  are  dis- 
tinctly seen,  viz., 
joint  faces ,  A,  B, 
(f7,  J,  /;  stratification-planes,  8  8  S,  gently  dipping  to  the  right ;  and 
cleavage-planes,  highly  inclined,  D  D,  cutting  through  both.  Cleavage- 
planes  are  therefore  not  stratification-planes. 


D  J 

FIG.  159.— Strata,  Cleavage-Planes,  and  Joints. 


CLEAVAGE   STRUCTURE. 


183 


Again,  it  has  been  compared  to  crystalline  cleavage,  on  a  huge  scale. 
It  has  heen  supposed  that  electricity  traversing  the  earth  in  certain  di- 
rections, while  certain  rocks  were  in  a  semi-fluid  or  plastic  state  through 
heat,  arranged  the  particles  of  such  rocks  in  a  definite  way,  giving  rise 
to  easy  splitting  in  definite  directions.  In  support  of  this  view  it  was 
urged  that  cleaved  slates  are  most  common  in  metamorphic  regions ; 
and  metamorphism,  as  we  shall  see  hereafter  (p.  221  et  seq.),  indicates 
the  previous  plastic  state  of  rocks,  which  is  a  necessary  condition  of  the 
rearrangement  of  the  particles  by  electricity.  The  great  objections  to 
this  theory  are — 1.  That  the  cleavage  is  not  like  crystalline  cleavage, 
between  ultimate  molecules,  and  therefore  perfectly  smooth,  bufr  be- 
tween discrete  and  quite  visible  granules ;  and,  2.  That  although  the 
phenomenon  is  indeed  most  common  in  metamorphic  rocks,  yet  meta- 
morphism is  by  no  means  a  necessary  condition  ;  on  the  contrary,  when 
the  real  necessary  conditions  are  present,  the  less  the  metamorphism 
the  more  perfect  the  cleavage. 

It  is  evident,  therefore,  that  slaty  cleavage  is  not  due  to  any  of  the 
causes  spoken  of  above.  It  is  not  flag-stone  cleavage,  nor  crystalline 
cleavage,  and  of  course  can  not  be  organic  cleavage. 

Sharpe's  Mechanical  Theory. — The  first  decided  step  in  the  right 
direction  was  made  by  Sharpe.  According  to  him,  slaty  cleavage  is  al- 
ways due  to  powerful  pressure  at  right  angles  to  the  planes  of  cleavage^ 
by  which  the  pressed  mass  has  been  compressed  in  the  direction  of  press- 
ure and  extended  in  the  direction  of  the  dip  of  the  cleavage-planes. 
This  theory  may  be  now  regarded  as  completely  established  by  the 
labors  of  Sharpe,  Sorby,  Haughton,  Tyndall,  and  others.  We  will  give 
a  few  of  the  most  important  observations  which  establish  its  truth. 

(a.)  Distorted  Shells. — Many  cleaved  slates  are  full  of  fossils.  In 
such  cases  the  fossils  are  always  crushed  and  distorted  as  if  by  powerful 
pressure,  their  diame- 
ter being  shortened 
at  right  angles  to  the 
cleavage,  and  greatly 
increased  in  the  di- 
rection of  the  cleav- 
age-planes. The  fol- 
lowing figures  (Fig. 
160)  are  examples  of 
distortion  by  press- 
ure. In  Fig.  160,  ZZ 

gives  the   direction  of  Fl°'  160-Distorted  F<**il8  <•»*  S*arpe). 

the  planes  of  cleavage ;  Figs.  1,  2,  3,  4,  represent  one  species  ;  5,  6,  7,  8, 
another.  In  Fig.  161  still  another  species  is  represented  in  the  natural 
and  distorted  forms. 


184 


STRATIFIED   OR   SEDIMENTARY   ROCKS. 


(b.)  Association  ivitli  Foldings. — Cleavage  is  alwaj's  associated  with 
strong  foldings  and  contortions  of  the  strata.     The  folding  of  the 
strata  is  produced  by  horizontal   pressure ;   the' 
strike  of  the  strata,  or  the  direction  of  the  anti- 
clinal and  synclinal  axes,  being  of  course  at  right 
B 


FIG.  161.— Cardium  Ilillanum:  A,  natural  form;  B  and  C,  deformed  by  pressure. 

angles  to  the  direction  of  pressure.     Now,  if  cleavage  is  produced  by 
the  same  pressure  which  folded  the  strata,  then  in  this  case  we  ought 

to  find  the  cleavage-planes 
highly  inclined,  and  their 
strike  parallel  with  the 
strike  of  the  strata ;  and 
such  we  find  is  usually  the 
fact.  In  Fig.  1G2  the 
heavy  lines  represent  the 

FIG.  162.-Cleavage-Plane8  intersecting  Strata.  gtrata  and    the    1Jght  lineg 

the  cleavage-planes,  both  outcropping  on  a  nearly  level  surface,  and 
parallel  to  each  other. 

(c.)  Association  with  Contorted  Laminae. — The  last  evidence  was 
taken  from  foldings  on  a  grand  scale  of  the  crust  of  the  earth ;  but 
even  fine  lines  of  lamination  are  often  thrown  into 
intricate  foldings  by  squeezing  together  in  the  di- 
rection of  the  lamination-planes.  In  such  case,  of 
course,  the  cleavage  ought  by  theory  to  be  at  right 
angles  to  the  original  direction  of  the  lamination, 
and  in  such  direction  we  actually  find  them.  Fig. 
163  represents  a  block  of  rock  in  which  three 
lamination-lines  are  visible.  The  lower  one,/d, 
consists  of  coarse  sand  which  could  not  mash,  and 
therefore  has  been  thrown  into  folds.  As  the 
specimen  stands  in  the  figure,  the  pressure  has 
been  horizontal ;  the  perpendicular  lines  represent 
the  position  of  the  cleavage-planes.  Fig.  164  rep-  FIG. 
resents  a  beautiful  specimen  of  laminated  slate,  in  (after  Tyndall>- 
which  the  lamination-planes  have  been  thrown  into  folds  by  pressure. 
The  direction  of  the  pressure  is  obvious.  The  planes  of  cleavage  are 
parallel  to  the  face,  c  p,  and  therefore  at  right  angles  to  the  pressure. 

(d.)  Flattened  Nodules. — In  some  finely-cleaved  slates,  such  as  are 
used  for  writing-slates,  it  is  common  to  find  small  light-greenish,  ellip- 


CLEAVAGE   STRUCTURE. 


185 


tical  spots  of  finer  material.  In  clay-deposits  of  the  present  day  it  is 
also  common  to  find  imbedded  little  round  nodules  of  finer  material. 
It  is  probable  that  the  greenish 
nodules  in  slate  were  also 
rounded  nodules  of  finer  clay  in 
the  original  clay-deposit  from 
which  the  slate  was  formed  by 
consolidation.  But  in  cleaved 
slates  these  nodules  are  always 
very  much  flattened  in  the  di- 
rection at  right  angles  to  the 
cleavage-planes,  and  spread  out 
in  the  direction  of  these  planes. 
(e.)  Experimental  Proof. — 
Finally,  experiments  by  Sorby 
and  by  Tyndall  show  that  clay 
(the  basis  of  slates),  when  sub- 
jected to  powerful  pressure,  ex- 
hibits always  a  cleavage,  often 
a  very  perfect  cleavage,  at  right 
angles  to  the  line  of  pressure.  FlG-  164-~A  Block  of  cleaved  Slate  <after  Juke8>- 

Physical  Theory. — Cleavage  is  certainly  produced  by  pressure,  but 
the  question  still  remains :  How  does  pressure  produce  planes  of  easy 
splitting  at  right  angles  to  its  own  direction  ?  What  is  the  physical 
explanation  of  cleavage  ? 

Sorby's  Theory.* — Mr.  Sorby's  view  is  that  all  cleaved  rocks  con- 
sisted, at  the  time  when  this  structure  was  impressed  upon  it,  of  a  plastic 

mass,  with  unequiaxed  foreign  particles  dis- 
seminated through  it ;  and  that  by  pressure 
the  unequiaxed  particles  were  turned  so  as 
to  firing  their  long  diameters  in  a  direction 
more  or  less  nearly  at  right  angles  to  the 
line  of  pressure,  and  thus  determined  planes 
of  easy  fracture  in  that  direction.  Usually, 
as  in  slates,  the  plastic  material  is  clay,  and 
the  unequiaxed  particles  are  mica-scales. 
Let  A,  Fig.  165,  represent  a  cube  of  clay 
with  mica  disseminated.  If  such  a  cube  be 
dried  and  broken,  the  fracture  will  take 
place  principally  along  the  surfaces  of  the 
mica,  which  may  therefore  be  seen  glisten- 
inS  on  the  uneven  surface  of  the  fracture; 


B 


*  Philosophical  Magazine,  second  series,  vol.  xi,  p.  20. 


186 


STRATIFIED  OR  SEDIMENTARY  ROCKS. 


00%  0 


c\ 


but  if  the  cube,  while  still  plastic,  be  pressed  into  a  flattened  disk,  then 
the  scales  are  turned  with  their  long  diameters  in  the  direction  of  ex- 
tension and  at  right  angles  to  the  line  of  pressure,  as  in  j9,  Fig.  165, 
and  the  planes  of  easy  fracture,  being  still  determined  by  these  sur- 
faces, will  be  in  that  direction. 

In  proof  of  this  view,  Mr.  Sorby  mixed  clay  with  mica-scales  or 
with  oxide-of-iron  scales,  and,  upon  subjecting  the  mass  to  powerful 
compression  and  drying,  he  always  found  a  perfect  cleavage  at  right 
angles  to  the  line  of  pressure.  Furthermore,  by  microscopic  examina- 
tion he  found  that  both  in  the  pressed  clay  and  in  the  cleaved  slates 
the  mica-scales  lay  in  the  direction  of  the  cleavage-planes. 

Although  cleavage  is  most  perfect  in  slates,  yet  other  rocks  are 
sometimes  affected  with  this  structure.  vln  a  specimen  of  cleaved  lime- 
stone, Sorby  found  under  the  microscope 
unequiaxed  fragments  of  broken  shells, 
corals,  crinoid  stems,  etc.  (organic  parti- 
cles), in  a  homogeneous  limestone-paste, 
lying  with  their  long  diameters  in  the  di- 
rection of  cleavage.  Originally  the  lime- 
stone was  a  lime-mud  with  (he  supposes) 
unequiaxed  organic  particles  disseminated. 
In  some  cases,  however,  Sorby  recognized 
the  very  important  fact  that  the  organic 
fragments  which  were  encrinal- joints,  had 
been  flattened  ly  pressure — had  changed 
their  form  instead  of  their  position.  A, 
FIG.  lee.— illustrating  Sorby's  Theory  Fig.  166,  gives  a  section  of  the  mass  in  the 

supposed  original  condition,   and   B  the 

condition  after  pressure.  This  observation  contained  the  germ  'of  the 
theory  proposed  by  Tyndall. 

Tyndall's  Theory.* — Tyndall  was  led  to  reject  Sorby's  theory  by  the 
observation  that  cleavage  structure  was  not  confined  to  masses  contain- 
ing unequiaxed  particles  of  any  kind,  but,  on  the  contrary,  the  cleavage 
is  more  perfect  in  proportion  as  the  mass  is  free  from  all  such  particles. 
Clay,  deprived  of  the  last  trace  of  foreign  particles  by  the  sorting  power 
of  water,  when  pressed,  cleaved  in  the  most  perfect  manner.  Common 
beeswax,  flattened  by  powerful  pressure  between  two  plates  of  glass 
and  then  hardened  by  cold,  exhibits  a  most  beautiful  cleavage  structure. 
Almost  any  substance — curds,  white-lead  powder,  plumbago — subjected 
to  powerful  pressure,  exhibits  to  some  extent  a  similar  structure.  Tyn- 
dall explains  these  facts  thus :  Nearly  all  substances,  except  vitreous, 
have  a  granular  or  a  crystalline  structure,  i.  e.,  consist  entirely  of  dis- 


fj 


Philosophical  Magazine,  second  series,  vol.  xii,  p.  35. 


CLEAVAGE   STRUCTURE.  187 

crete  granules  or  crystals,  with  surfaces  of  easy  fracture  between  them. 
When  such  substances  are  broken,  the  fracture  takes  place  between  the 
crystals  or  granules,  producing  a  rough  crystalline  or  granular  surface, 
entirely  different  from  the  smooth  surface  of  vitreous  fracture.  Marble, 
cast  iron,  earthenware,  and  clay,  are  good  examples  of  crystalline  and 
granular  structure.  Now,  if  a  mass  thus  composed,  yield  to  pressure, 
every  constituent  granule  is  flattened  into  a  scale,  and  the  structure  be- 
comes scaly  ;  and  as  the  surfaces  of  easy  fracture  will  still  be  between 
the  constituent  scales,  we  have  cleavage  at  right  angles  to  the  line  of 
pressure.  A  mass  of  iron,  just  taken  from  the  puddling-furnace  and 
cooled,  exhibits  a  granular  structure ;  but  if  drawn  out  into  a  bar,  each 
granule  is  extended  into  a  thread,  and  the  structure  becomes  fibrous  ; 
or  if  rolled  into  a  sheet,  each  granule  is  flattened  into  a  scale,  and  we 
have  a  cleavage  structure. 

There  can  be  little  doubt  that  this  is  the  true  explanation  of  slaty 
cleavage.  The  change  of  form  which,  as  we  have  seen,  has  taken  place 
in  the  fossil-shells,  encrinal  joints,  and  rounded  nodules,  has  affected 
every  constituent  granule  of  the  original  earthy  mass,  so  that  the  struct- 
ure becomes  essentially  scaly  instead  of  granular ;  the  cleavage  being 
between  the  constituent  scales.  Sorby,  it  is  true,  in  his  observations 
on  cleaved  limestones,  recognized  the  true  cause  of  cleavage,  viz.,  the 
change  of  form  of  discrete  particles ;  but  he  regarded  this  as  subordi- 
nate to  change  of  position.  Besides,  the  particles  of  Sorby  were/or- 
eign,  which  Tyndall  has  shown  to  be  unnecessary ;  while  the  particles 
of  Tyndall  are  constituent. 

Geological  Application. — It  may  be  considered,  therefore,  as  certain 
that  cleaved  slates  have  assumed  their  peculiar  structure  under  the  in- 
fluence of  powerful  pressure  at  right  angles  to  the  cleavage-planes,  by 
which  the  whole  squeezed  mass  is  mashed  together  in  one  direction  and 
extended  in  another.  Taking  any  ideal  sphere  in  the  original  unsqueezed 
mass :  after  mashing  the  diameter  in  the  line  of  pressure  has  been  short- 
ened, the  diameter  in  the  line  of  cleavage-^  has  been  correspondingly 
extended,  and  the  diameter  in  the  line  of  cleavage-strike  unaffected  (since 
extension  of  this  diameter  in  any  place  must  be  compensated  by  short- 
ening in  a  contiguous  place  right  or  left) ;  so  that  the  original  sphere  has 
been  converted  into  a  greatly-flattened  ellipsoid  of  three  unequal  diame- 
ters. The  amount  of  compression  and  extension  may  be  estimated  in 
the  case  a  by  the  amount  of  distortion  of  shells  of  known  form  (Figs. 
160  and  161) ;  in  the  case  c  by  a  comparison  of  the  transverse  diame- 
ter of  the  block  with  the  length  of  the  folded  line  /  d  (Fig.  163);  in 
the  case  d  by  the  relation  between  the  diameters  of  the  elliptic  spots. 
By  these  means,  but  principally  by  the  first,  Haughton  *  has  estimated 

*  Philosophical  Magazine,  fourth  series,  vol.  xii,  p.  409. 


188 


STRATIFIED   OR   SEDIMENTARY  ROCKS. 


that  an  original  ideal  sphere  has  been  changed  into  an  ellipsoid,  whose 
greatest  and  shortest  diameters  are  to  each  other,  in  some  cases,  as  2  : 1, 
in  others  as  3  :  1,  4  :  1,  6  or  7  :  1,  9:1,  and  in  some  even  11:1.  The 
average  in  well-cleaved  slates,  according  to  Sorby,  is  about  6:1.  Now, 
since  this  ratio  is  the  result  partly  of  compression  and  partly  of  exten- 
sion, it  is  evident  that  either  the  compression  alone  or  the  extension 
alone  would  be  the  square  roots  of  these  ratios.  Therefore,  we  may 
assume  the  average  compression  as  2%  :  1,  and  the  average  extension 
as  1  :  2-J. 

It  is  impossible  to  overestimate  the  geological  importance  of  these 
facts.  Whole  mountains  of  strata,  whole  regions  of  the  earth's  crust, 
are  cleaved  to  great  and  unknown  depths,  showing  that  the  crust  has 
been  subjected  to  an  almost  inconceivable  force,  squeezing  it  together 
in  an  horizontal  direction  and  swelling  it  upward.  This  upward  swell- 
ing, or  thickening  of  the  strata  by  lateral  squeezing,  is  a  probable  cause 
of  gradual  elevation  of  the  earth's  crust,  which  has  not  been  noticed  by 
geologists.  We  will  speak  again  of  this  important  subject  in  our  dis- 
cussion of  mountain-formation. 

There  are  reasons  for  believing  that  the  squeezing  did  not  take 
place,  and  the  structure  was  not  formed,  while  the  strata  were  in  their 
original  condition  of  plastic  sediment,  but  after  they  had  been  consoli- 
dated into  rock  and  the  contained  fossils  had  been  completely  petrified, 
otherwise  the  shells  must  have  been  broken  by  the  pressure.  Yet,  on 
the.  other  hand,  some  degree  of  plasticity  seems  absolutely  necessary  to 
account  for  so  great  a  compression  in  one  direction  and  extension  in 
another  without  disintegration  of  the  mass.  It  seems  most  probable 
that  at  the  time  the  structure  was  produced  these  rocks  were  deeply 
buried  beneath  other  rocks  and  in  a  somewhat  plastic  state,  through 
the  influence  of  heat  in  the  presence  of  water.  Afterward,  they  were 
exposed  by  erosion. 

Nodular  or  Concretionary  Structure. 

In  many  stratified  rocks  are  found  nodules  of  various  forms  scattered 
through  the  mass  or  in  layers  parallel  to  the  planes  of  stratification. 
Like  slaty  cleavage,  this  structure  is  the  result  of  internal  changes  sub- 


FIG.  167. 


FIG.  168. 


sequent  to  the  sedimentation  ;  for  the  planes  of  stratification  often  pass 
directly  through  the  nodules  (Figs.  167  and  168).     The  flint  nodules  of 


NODULAR   OR   CONCRETIONARY   STRUCTURE. 


189 


PIG-  m 


the  chalk,  and  the  clay  iron-stone  nodules  of  the  coal  strata  and  hy- 
draulic lime-balls,  common  in  many  clays,  are  familiar  illustrations  of 
this  structure. 

Cause.  —  Nodular  concretions  seem  to  occur  whenever  a  more  solu- 
ble or  more  suspensible  substance  is  diffused  in  small  quantities  through 
a  mass  of  entirely  different  and  more  fixed  material.  Thus,  if  strata  of 
sandstone  or  clay  have  small  quantities  of  carbonate  of  lime  or  carbon- 
ate of  iron  diffused  through  them,  the  diffused  particles  of  lime  or  iron 
will  gradually,  by  a  process  little  under- 
stood, segregate  themselves  into  more  or 
less  spherical  or  nodular  masses,  in  some 
cases  almost  pure,  but  generally  inclos- 
ing a  considerable  quantity  of  the  mate- 
rial of  the  strata.  In  this  manner  lime- 
balls  and  iron-ore  balls  and  nodules,  so 
common  in  sandstones  and  clays,  are 
formed.  In  like  manner,  the  Hint  nod- 
ules  of  the  chalk  were  formed  by  the 
segregation  of  silica,  originally  diffused 
in  small  quantities  through  the  chalk-sediment.  Very  often  some  for- 
eign substance  forms  the  nucleus  about  which  the  segregation  com- 
mences. On  breaking  a  nodule  open,  a  shell  or  some  other  organism  is 
often  found  beautifully  preserved.  These  nodules,  therefore,  are  a 
fruitful  source  of  beautiful  fossils.  In  most  cases,  probably  in  all 
cases,  the  segregating  substance  must  have  been  to  some  extent  soluble 
in  water  pervading,  or  suspensible  iir  water  percolating  the  stratum; 
and  the  reason  why  they  are  so  frequently  associated  with  fossils  is  that 
decomposing  organic  matter  renders  many  substances  such  as  lime 
carbonate,  iron  oxide  and  silica  more  soluble.  Sometimes  the  nodules 

run  together,  forming  a 
more  or  less  continuous 
stratum  (Fig.  173).  In  such 
cases,  the  segregating  mate- 
rial is  more  impure. 

Forms  of  Nodules.—  The 
typical  and  most  common 
form  is  globular.  This  is 
well  seen  in  lime-balls  and 
iron-balls.  Sometimes  these 
balls  are  solid,  sometimes 
they  have  irregular  cracks 
in  the  center  (Fig.  169), 
sometimes  they  have  a  radiated  structure  (Fig.  170),  sometimes  they 
are  hollow  like  a  shell  (this  is  common  in  iron-balls).  They  vary  in  size 


FIG.  170. — Dolomite  containing  Concretions,  Sunderland 
(after  Jukes). 


190 


STRATIFIED   OR  SEDIMENTARY  ROCKS. 


FIG.  171.— A  Curious  Form  of  Concretion  (after  Gratacap). 


from  that  of  a  pea  to  six  and  eight  feet  in  diameter.  Often,  however, 
instead  of  the  spherical  form,  they  take  on  various  and  strange  and 
fantastic  shapes  (Fig.  171),  sometimes  like  a  dumb-bell,  sometimes  a 
flattened  disk,  sometimes  a  ring,  sometimes  a  flattened  ellipsoid,  regu- 
larly seamed  on  the  surface  like  the  shell  of  a  turtle  (turtle-stones). 
They  are  often  mistaken  by  unscientific  observers  for  fossils. 

Kinds  of  Nodules  found  in  Different  Strata.— In  sandstone  strata  the 
nodules  are  commonly  carbonate  of  lime  or  oxide  of  iron  (lime  or  iron 

balls).  In  clay 
strata  they  are 
carbonate  of  lime 
or  carbonate  of 
iron  (clay  iron- 
stone of  coal 
strata),  or  a  mix- 
ture of  these 
(Roman  cement 
nodules  of  the 
London  clay). 

In  limestone  the  nodules  are  always  silica,  and  conversely  silica 
nodules  are  peculiar  to  limestone.  The  flint  nodules  of  the  chalk  are 
remarkable  for  being  arranged  in  planes  parallel  to  the  planes  of  strati- 
fication (Fig.  172). 
Sometimes  the  sili- 
ceous matter  segre- 
gates in  continuous 
strata  of  siliceous 
limestone  (Fig.  173). 

In  the  cases  thus 
far  spoken  of,  the  nod- 
ules are  scattered 
through  the  mass  of 
the  strata  or  arranged 
in  planes  parallel  to 
the  planes  of  stratifi- 
cation. But  in  some 
cases  the  whole  mass  of  the  rock  assumes  a  concretionary  or  concentric 
structure.  The  cause  of  this  is  still  more  difficult  to  explain, 

FOSSILS  :  THEIR  ORIGIN  AND  DISTRIBUTION. 

Stratified  rocks,  as  we  have  already  seen,  are  sediments  accumulated 
in  ancient  seas,  lakes,  deltas,  etc.,  and  consolidated  by  time.  As  now, 
so  then,  dead  shells  were  imbedded  in  shore-deposits ;  leaves  and  logs  of 
high  land-plants,  and  bones  of  land-animals,  .were  drifted  into  swamps 


FIG.  172.— Chalk-Cliffs  with  Flint  Nodules. 


FOSSILS:   THEIR   ORIGIN   AND   DISTRIBUTION. 


101 


Fio.  173. — Chalk-Cliffs. 


and  deltas  and  buried  in  mud ;  and  tracks  were  formed  on  flat,  muddy 
shores  by  animals  walking  on  them.  These  have  been  preserved  with 
more  or  less  change,  and  are 
even  now  found  in  great 
numbers  inclosed  in  strati- 
fied rocks.  They  are  called 
fossils.  A  fossil,  therefore, 
is  any  evidence  of  the  for- 
mer existence  of  a  living  be- 
ing. Fossils  are  the  remains 
of  the  faunas  and  floras  of 
previous  geological  epochs. 
Their  presence  is  the  most 
constant  characteristic  of 
stratified  rocks. 

Degrees  of  Preservation. 
— Sdmetimes  only  the  tracks 
of  animals,  or  impressions  of  leaves  of  plants,  are  preserved.  More 
commonly  the  bones  or  shells,  or  other  hard  parts  of  animals,  are  pre- 
served with  various  degrees  of  change.  Sometimes  even  the  soft  and 
more  perishable  tissues  are  preserved.  "We  will  treat  of  these  degrees 
under  three  principal  heads  : 

1.  Decomposition  prevented  and  the   Organic  Matter  more  or  less 
completely  preserved. — Cases  of  this  kind  are  usually  found  in  compar- 
atively recent  strata,  and  imbedded  either  in  frozen  soils,  or  in  peat,  or 
in  stiff  clays ;  although  some  cases  of  partial  preservation  of  the  or- 
ganic matter  are  found  even  in  old  rocks.    Extinct  elephants  have  been 
found  frozen  in  the  river-bluffs  of  Siberia  so  perfectly  preserved  that 
dogs  and  wolves  ate  their  flesh.     Skeletons  of  men  and  animals  are 
found  in  peat-bogs  and  stiff  clays  of  a  comparatively  recent  formation, 
the  organic  matter  of  which  is  still  preserved.     In  clays  of  the  Tertiary 
period  the  imbedded  shells  still  retain  the  epidermis,  and  even  in  the 
Lias  (Mesozoic)  shells  are  found  retaining  the  nacreous  luster.     Coal  is 
vegetable  matter  changed  but  not  destroyed.     It  is  found  in  almost 
every  formation,  even  down  to  the  oldest.    Every  degree  of  change  may 
be  traced  in  different  specimens  of  fossil  wood,  between  perfect  wood 
and  perfect  coal. 

2.  Petrifaction:  Organic  Form  and  Structure  preserved. — In  the 
last  case  the  organic  matter  is  more  or  less  preserved.     In  the  case 
now  to  be  described  the  organic  matter  is  entirely  gone ;  but  the  or- 
ganic form  and  the  organic  structure  are  preserved  in  mineral  matter. 
This  is  what  is  usually  called  petrifaction  or  mineralization.     The  best 
example  of  this  is  petrified  wood.     In  a  good  specimen  of  petrified 
wood,  not  only  the  external  form  of  the  trunk,  not  only  the  general 


192  STRATIFIED   OR  SEDIMENTARY   ROCKS. 

structure  of  the  stem — viz.,  pith,  wood,  and  bark — not  only  the  radiating 
silver-grain  and  the  concentric  rings  of  growth,  are  discernible,  but 
even  the  microscopic  cellular  structure  of  the  wood,  and  the  exquisite 
sculpturings  of  the  cell-walls  themselves,  are  perfectly  preserved,  so 
that  the  kind  of  wood  may  often  be  determined  by  the  microscope  with 
the  utmost  certainty.  Yet  not  one  particle  of  the  organic  matter  of 
the  wood  remains.  It  has  been  entirely  replaced  by  mineral  matter; 
usually  by  some  form  of  silica.  The  same  is  true  of  shells  and  bones 
of  animals ;  but  as  shells  and  bones  consist  naturally  partly  of  organic 
and  partly  of  mineral  matter,  very  often  it  is  only  the  organic  matter 
which  is  replaced,  although  sometimes  the  original  mineral  matter  is 
also  replaced  by  silica  or  other  mineral  substance.  The  radiating 
structure  of  corals  or  the  microscopic  structure  of  teeth,  bones,  and 
shells,  is  often  beautifully  preserved.  This  kind  of  preservation  for 
shells  and  corals  is  most  common  in  limestones  and  clays ;  for  wood,  in 
gravels. 

Theory  of  Petrifaction. — If  wood  be  soaked  in  a  strong  solution  of 
sulphate  of  iron  (copperas)  and  dried,  and  the  same  process  be  repeat- 
ed until  the  wood  is  highly  charged  with  this  salt,  and  then  burned, 
the  structure  of  the  wood  will  be  roughly  preserved  in  the  peroxide  of 
iron  left.  Also,  it  is  well  known  that  the  smallest  fissures  and  cavities 
in  rocks  are  speedily  filled  by  infiltrating  waters  with  mineral  matters. 
Now,  wood  buried  in  soil  soaked  with  some  petrifying  material  becomes 
highly  charged  with  the  same,  and  the  cells  filled  with  infiltrated  mat- 
ter, and  when  the  wood  decays  the  petrifying  material  is  left,  retaining 
the  structure  of  the  wood.  But  this  is  not  all,  for  in  Nature  there  is 
an  additional  process,  not  illustrated  either  by  the  experiment  or  by 
the  example  of  infiltrated  fillings.  As  each  particle  of  organic  matter 
passes  away  by  decay,  a  particle  of  mineral  matter  takes  its  place,  until 
finally  the  whole  of  the  organic  matter  is  replaced.  Petrifaction,  there- 
fore, is  a  process  of  substitution,  as  well  as  interstitial  filling.  Now, 
it  so  happens,  probably  from  the  different  nature  of  the  process  in  the 
two  cases,  that  the  interstitial  filling  always  differs,  either  in  chemical 
composition  or  in  color,  from  the  substituted  mate- 
rial. Thus  the  structure  is  still  visible,  though  the 
mass  is  solid.  If  Fig.  174  represent  a  cross-section  of 
three  petrified  wood-cells,  the  matter  filling  the  cells 
(b)  is  always  different  from  the  matter  forming  the 
cell-wall  (a). 

The  most  common  petrifying  materials  are  silica, 
carbonate  of  lime,  and  sulphide  of  iron  (pyrites).  In  the  case  of  petri- 
faction by  pyrites  the  process  is  quite  intelligible,  but  the  structure  is 
usually,  very  imperfectly  preserved.  If  water  containing  sulphate  of 
iron  (FeSOJ  come  in  contact  with  decaying  organic  matter,  the  salt  is 


FOSSILS:   THEIR  ORIGIN  AND   DISTRIBUTION.  193 

deoxidized  by  the  organic  matter,  the  latter  passing  off  as  carbonic  acid 
and  water,  and  the  former  becomes  insoluble  sulphide  (FeS),  and  is 
deposited.  Now,  as  each  particle  of  organic  matter  passes  away  as 
CO 2  and  IPO,  the  molecule  of  iron  sulphate  which  effected  the  change 
is  itself  changed  into  insoluble  sulphide,  and  takes  its  place. 

The  process  of  replacement  by  silica  (silification)  is  less  clear,  but 
it  is  probably  as  follows :  Silica  is  found  in  solution  in  many  waters, 
being  held  in  this  condition  by  small  quantities  of  alkali  present  in  the 
waters.  In  contact  with  decomposing  wood  the  alkali  is  neutralized 
by  the  humic,  ulmic,  and  other  acids  of  decomposition,  and  the  silica 
therefore  deposited. 

3.  Organic  Form  only  preserved. — In  the  third  case  organic  mat- 
ter and  organic  structure  are  both  lost,  and  only  organic  form  is  pre- 
served. This  kind  of 
fossilization  is  most  com- 
monly seen  in  shells.  It 
may  be  subdivided  into 
four  subordinate  cases, 
represented  in  section  by 
«,  #,  c,  and  d  of  Fig.  175. 
In  this  figure  the  horizontal  lines  represent  the  original  sediment  which 
may  or  may  not  have  consolidated  into  rock ;  the  vertical  lines  repre 
sent  a  subsequent  filling  of  different  and  usually  finer  material.  In  a 
we  have  a  mold  of  the  external  form  of  the  shell  preserved  in  sediment. 
The  shell  with  the  undecayed  animal  was  imbedded,  and  afterward  en- 
tirely dissolved  away,  leaving  only  the  hollow  mold.  In  b  the  same 
process  has  taken  place,  only  the  mold  has  been  subsequently  filled  by 
infiltration  of  slightly  soluble  matters.  In  this  case  we  have  both  the 
mold  and  the  cast  of  the  external  form  ;  the  mold  being  formed  of  sed- 
iment, and  the  cast  of  infiltrated  matter.  These  are  always  of  different 
materials,  i.  e.,  different  either  in  chemical  composition  or  in  state  of 
aggregation.  In  c  we  have  a  mold  of  the  external  form  in  sediment, 
and  a  cast  of  the  internal  form  in  the  same  material  with  an  empty 
space  between,  having  the  exact  form  and  thickness  of  the  shell.  In 
this  case,  the  already  dead  and  empty  shell  was  imbedded  in  sediment, 
which  also  filled  its  interior  ;  afterward  the  shell  was  removed,  leaving 
an  empty  space.  In  d  this  empty  space  was  subsequently  filled  by 
infiltration.  In  shore  and  river  deposits  of  the  present  day  it  is  very 
common  to  find  shells  imbedded  in,  and  filled  with,  sand  or  mud.  In 
the  more  recent  tertiary  rocks  shells  are  commonly  found  in  the  same 
condition  precisely ;  but  in  the  older  rocks  more  commonly  the  origi- 
nal shell  is  removed,  and  the  space  either  left  empty  or  filled  by  infil- 
tration. Cases  c  and  d  are  well  represented  by  Figs.  176, 177,  and  178. 
Cases  like  a  and  c  are  most  commonly  found  in  porous  rocks  like  sand- 
13 


194 


STRATIFIED   OR  SEDIMENTARY   ROCKS. 


stone ;  J  and  J,  especially  the  latter,  are  found  in  all  kinds  of  rocks. 
By  far  the  most  common  infiltration  fillings  are  carbonate  of  lime  and 
silica. 

Often  we  find  impressions  of  the  forms  of  small  portions  only  of  the 
original  organism,  as  of  the  leaves  of  trees,  or  the  feet  of  animals  walk- 


FIG.  176.— a,  Cast  of  interior; 
6,  natural  form. 


FIG.  177.— a,  Natural  form; 
6,  cast  of  interior  and 
mold  of  exterior. 


FIG.  178.— Trigonia  Longa,  showing 
cast  (a)  of  the  exterior  and  (6)  of 
the  interior  of  the  shell. 


ing  on  the  soft  mud  of  the  flat  shores  of  ancient  bays.  Such  tracks 
were  afterward  covered  up  with  river  or  tidal  deposit,  and  thus  pre- 
served. On  cleaving  the  rock  along  the  lamination-planes  we  have  on 
one  side  a  mold  and  on  the  other  the  cast  of  the  foot. 

Between  cases  1  and  2  every  stage  of  gradation  may  be  traced. 
The  amount  of  change,  as  a  general  fact,  varies  with  the  age  of  the 
rock  ;  *but  is  still  more  dependent  on  the  kind  of  rock  and  the  degree 
of  metamorphism.  In  an  impermeable  rock,  like  clay,  the  changes  are 
much  more  slow  than  in  a  porous  rock,  like  sandstone. 

Distribution  of  Fossils  in  the  Strata. 

The  nature  of  the  fossil  species  found  in  rocks  is  determined  partly 
by  the  kind  of  rock,  partly  by  the  country  where  the  rock  is  found,  and 
partly  by  the  age  of  the  rock. 

1.  Kind  of  Rock. — It  is  well  known  that  the  species  of  lower  marine 
animals  vary  with  the  depth.  They  also  vary  with  the  kind  of  bottom. 
Thus,  along  shore-lines  and  on  sand-bottom  the  species  differ  from 
those  in  deep  water  and  on  mud-bottom.  Shells  are  found  mostly 
along  shore-lines,  corals  in  opener  seas,  and  foraminifera  in  deep  seas. 
The  same  was  true  in  every  previous  epoch.  We  might  expect,  there- 
fore, and  do  find,  that  the  lower  marine  fossils  of  sandstones,  shales, 
and  limestones,  differ  even  when  these  strata  belong  to  the  same  coun- 
try and  geological  epoch.  The  higher  marine  animals,  such  as  fishes, 
cuttle-fish,  etc.,  swimming  freely  in  the  sea,  are  more  independent  of 
bottoms,  and  we  find  their  skeletons  and  shells  equally  in  all  kinds  of 
strata.  Land  animals  perish  on  land,  and  their  skeletons  are  drifted 
into  bays,  river-deltas,  and  lakes,  and  buried  there  mostly  in  fresh- 


DISTRIBUTION   OF  FOSSILS   IN   THE  STRATA.  195 

-water  or  brackish-water  deposits  of  sand  and  clay.     It  is,  therefore,  in 
such  strata  that  their  remains  are  commonly  found. 

2.  The  Country  where  found. — It  is  also  well  known  that  the 
faunas  and  floras  of  different  countries  at  the  present  time  differ  as 
to  species,  and  often  as  to  genera  and  families ;  the  difference  being 
generally  in  proportion  to  the  difference  in  climate,  the  physical  bar- 
riers intervening,  and  the  length  of  time  during  which  the  barriers 
have  existed.     The  same  was  true  of  the  faunas  and  floras  of  previous 
epochs,  and  therefore  of  the  fossils  of  the  same  age  in  different  coun- 
tries.    The  fossil  species  of  the  same  epoch  in  America,  in  Europe 
and  in  Asia,  are  not  usually  identical,  although  there  may  be  a  general 
resemblance.     The  geographical  diversity,  however,  is  small  in  the 
lowest  and  oldest  rocks,  and  becomes  greater  and  greater  as  we  pass 
upward  into  newer  and  newer  rocks,  and  is  greatest  in  the  fauna  and 
flora  of  the  present  day. 

3.  The  Age. — This  introduces  the  subject  of  the  laws  of  distri- 
bution of  organisms  in  time,  or  of  fossils  vertically  in  the  series  of 
stratified  rocks.     The  subject  will  be  more  fully  treated  in  Part  III, 
of  which  it  constitutes  the  principal  portion.     We  now  bring  out  only 
so  much  as  is  necessary  as  a  basis  of  classification  of  stratified  rocks. 

(a.)  Geological  Fauna  and  Flora. — As  we  pass  from  the  oldest  and 
lowest  rocks  upward  to  the  newest  and  highest,  we  find  that  all  the 
species,  most  of  the  genera,  and  many  of  the  families,  change  many  times. 
Now,  all  the  species  of  animals  and  plants  inhabiting  the  earth  at  one 
time  constitute  the  fauna  and  flora  of  that  geological  time.  Geological 
faunas,  therefore,  have  changed  many  times.  In  a  conformable  series 
of  rocks  the  change  from  one  fossil  fauna  or  flora  to  another  succeeding 
is  always  gradual,  the  species  of  the  later  fauna  or  flora  gradually 
replacing  those  of  the  earlier.  But  between  two  series  of  unconform- 
able  strata  the  change  is  sudden  and  complete — as  if  one  fauna  and 
flora  had  been  suddenly  destroyed  and  another  introduced.  It  must  be 
remembered,  however,  that  unconformity  always  indicates  a  great  lapse 
of  time  unrepresented  at  the  place  of  observation  by  strata  or  fossils. 
It  is  therefore  probable  that  the  apparent  suddenness  of  the  change  is 
only  the  result  of  our  ignorance  of  the  fauna  and  flora  of  the  period  un- 
represented. Nevertheless,  as  unconformity  always  indicates  changes 
of  physical  geography,  and  therefore  of  climate,  it  is  probable  that  in 
the  history  of  the  earth  there  were  periods  of  great  changes,  marked 
by  unconformity  of  strata,  during  which  changes  of  species  were  more 
rapid,  separated  by  periods  of  comparative  quiet,  marlced  by  conformity, 
during  which  the  species  were  either  unchanged,  or  changed  slowly. 
Such  a  period  is  called  a  geological  period  or  geological  epoch,  and 
the  rocks  formed  during  a  geological  period,  or  epoch,  is  called  a 
formation. 


196  STRATIFIED   OR   SEDIMENTARY   ROCKS. 

There  are,  therefore,  two  tests  of  a  formation  and  a  corresponding 
geological  period,  viz.,  1.  Conformity  of  the  strata  or  rock-system,  and, 
2.  General  similarity  of  fossils,  or  life-system.  There  are  also  two 
modes  of  separating  formations  and  corresponding  periods,  viz.,  un- 
conformity of  the  rock-system,  and  great  and  sudden  change  of  the 
life-system.  A  geological  formation,  therefore,  may  be  denned  as  a 
,  group  of  conformable  rocks  containing  similar  fossils,  usually  separated 
from  other  similar  groups  containing  different  fossils  by  unconformity. 
A  geological  period  may  be  defined  as  a  period  of  comparative  quiet, 
during  which  the  physical  geography,  climate,  and  fauna,  and  flora 
were  substantially  the  same,  usually  separated  from  other  similar  periods 
by  changes  of  physical  geography  and  climate,  which  resulted  in  changes 
of  fauna  and  flora.  Of  these  two  tests,  however,  the  life-system  is 
usually  considered  the  most  important,  and  in  case  of  disagreement 
must  control  classification. 

(b.)  Geological  Faunas  and  Floras  differ  more  than  Geographical 
Faunas  and  Floras. — If  there  were  no  geographical  diversity,  species 
of  the  same  age  would  be  identical  all  over  the  earth,  and  therefore  it 
would  be  easy  to  determine  strata  of  the  same  age  (geological  horizon). 
On  the  other  hand,  if  geographical  diversity  in  any  age  were  as  great 
as  the  diversity  between  two  successive  ages,  then  it  would  seem  im- 
possible to  establish  a  geological  horizon.  But  this  law  states  that  the 
'  difference  between  two  successive  faunas  is  greater  than  between  two 
contiguous  faunas.  In  other  words,  the  species  of  successive  periods, 
or  fossils  of  successive  formations,  dMer  from  each  other  more  than 
species  of  the  same  period  or  fossils  of\he  same  formation  in  different 
parts  of  the  earth.  There  is  a  general  similarity  in  the  species  of  the 
same  period  all  over  the  surface  of  the  earth.  Hence  by  comparison  of 
fossils  it  is  possible  to  determine  what  strata,  in  different  portions  of 
the  earth,  belong  to  the  same  period  (to  synchronize  strata).  The 
strata  all  over  the  earth,  which  were  formed  at  the  same  time,  are  said 
to  belong  to  the  same  geological  horizon.  Strata  of  the  same  horizon 
are  tleterminable  by  similarity  of  fossils  with  considerable  certainty, 
until  we  come  up  to  the  tertiary  rocks.  In  all  the  newer  rocks,  how- 
ever, the  geographical  diversity  is  so  great  as  to  interfere  seriously  with 
the  ability  to  synchronize  by  means  of  comparison  of  fossils.  Another 
method,  therefore,  is  used  for  these  higher  rocks. 

(c.)  Increasing  Likeness  to  Existing  Forms. — By  examining  and 
comparing  fossils  from  the  lowest  to  the  highest  rocks,  it  has  been  ob- 
served that  there  is  a  steady  approach  of  the  fossil  faunas  and  floras  to 
the  present  faunas  and  floras,  first  in  the  families,  then  in  the  genera, 
and  finally  in  the  species.  The  species  of  fossil  molluscous  shells  begin 
to  be  identical  with  molluscous  species  of  the  present  day  only  in  the 
tertiary  rocks,  and  the  proportion  of  identical  species  steadily  increases 


CLASSIFICATION   OF  STRATIFIED   ROCKS.  197 

as  we  pass  upward.  Thus  in  the  newer  rocks,  just  where  the  other 
method  (comparison  of  fossil  faunas  with  one  another)  begins  to  fail, 
we  may  synchronize  strata  of  different  localities,  by  comparing  their 
shell  fauna  with  the  shell  fauna  of  the  present  day,  in  the  same  locali- 
ties. Those  are  said  to  be  of  the  same  age  which  contain  the  same  per- 
centage of  shells  identical  ivith  those  of  the  present  day.  To  this  we 
may  add  that,  if  not  species,  at  least  many  genera  and  families,  especially 
among  vertebrates,  are  characteristic  of  each  horizon  even  of  the  newest 
rocks. 

SECTION  2.— CLASSIFICATION  OF  STRATIFIED  ROCKS. 

Geology  is  essentially  a  history.  Stratified  rocks  are  the  leaves  on 
which  this  history  is  recorded.  The  fundamental  idea  of  every  clas- 
sification is  therefore  relative  age.  The  object  to  be  attained  in  classi- 
fication is,  first,  to  arrange  all  rocks  in  chronological  order,  so  that  the 
history  may  be  read  as  it  was  written ;  and  then,  second,  to  collect  them 
into  larger  and  smaller  groups,  called  systems,  series,  formations,  cor- 
responding to  the  great  eras,  periods,  epochs,  of  the  earth's  history. 
There  are  several  different  methods  of  determining  the  relative  age  of 
rocks  : 

1.  Order  of  Superposition. — It  is  evident,  from  the  manner  in  which 
stratified  rocks  are  formed — viz.,  by  sedimentation — that  their  original 
position  indicates,  with  absolute  certainty,  their  relative  age,  the  lower 
being  older  than  the  higher.  If,  therefore,  the  original  position  of  any 
series  of  strata  be  retained  or  not  very  greatly  disturbed,  and  we  have 
a  good  section,  the  relative  age  of  the  strata  which  compose  the  series 
may  be  easily  determined.  But  the  strata,  as  we  have  already  seen, 
have  in  many  cases  been  crushed  and  contorted  and  folded  in  the  most 
intricate  manner,  sometimes  even  turned  over;  they  have  also  been 
broken  and  slipped,  and  large  masses  carried  away  by  erosion,  and  often 
so  changed  by  heat  and  other  agents,  that  their  stratification  is  nearly 
or  quite  obliterated.  For  these  reasons  it  is  often  very  difficult  to 
determine  the  relative  position,  and  thus  to  construct  an  ideal  sec- 
tion of  the  strata  of  a  series  of  rocks,  even  in  a  single  locality.  Nev- 
ertheless, the  method  of  superposition  is  conclusive,  and  takes  prece- 
dence of  all  others  whenever  it  can  be  applied.  In  spite  of  all  these 
difficulties,  if  the  whole  geological  series  were  present  in  any  one  lo- 
cality, it  would  be  comparatively  easy  to  construct  the  geological  chro- 
nology. 

But  a  series  of  rocks  in  any  one  locality  can  not  give  us  the  whole 
history  of  the  earth.  Since  sedimentation  only  takes  place  at  the  bot- 
tom of  water,  those  places  which  were  land-surfaces  during  any  geo- 
logical epoch  received  no  deposit,  and  therefore  the  strata  representing 
that  epoch  must  be  wanting  there.  Now,  as  there  have  been  frequent 


198  STRATIFIED   OR   SEDIMENTARY    ROCKS. 

oscillations  of  land-surfaces  and  sea-bottoms  in  past  times,  similar  to 
those  taking  place  at  the  present  time,  we  find  that  in  every  known 
local  series  of  strata  there  exist  many  and  great  gaps ;  so  many  and  so 
great  that  the  record  may  be  regarded  as  only  fragmentary.  Such  gaps 
are  usually  indicated  by  unconformity.  It  is  the  task  of  the  geologist, 
by  extensive  comparison  of  rocks  in  all  countries,  to  fill  up  these  gaps, 
and  make  a  continuous  series.  The  leaves  of  the  book  of  Time  are 
scattered  hither  and  thither  over  the  surface  of  the  earth,  and  it  is  the 
duty  of  the  geologist  to  gather  and  arrange  them  according  to'  their 
paging.  This  is  done  by  comparison  of  rocks  of  different  localities, 
partly  by  their  lithological  character,  but  principally  by  the  fossils 
which  they  contain. 

2.  Lithological  Character. — At  the  present  time,  in  our  seas  and 
lakes,  deposits  are  forming  composed  of  sand,  clay,  mud,  and  lime,  of 
every  kind,  in  different  localities.     The  same  has  taken  place  in  previ- 
ous epochs.     Sandstones,  limestones,  and  slates,  not  differing  greatly 
from  those  forming  at  the  present  time,  except  in  degree  of  consolida- 
tion, have  been  formed  in  every  geological  period.     Lithological  char- 
acter, therefore,  is  no  test  of  age.     In  comparing  rocks  of  widely-sepa- 
rated localities,  as,  for  example,  the  rocks  of  different  continents,  dif- 
ference of  lithological  character  is  no  evidence  of  difference  of  age,  nor 
similarity  of  lithological  character  of  any  value  in  determining  a  geo- 
logical horizon.     But,  as  deposits  are  now  being  formed  of  a  similar 
character  over  considerable  areas,  so  also  we  find  strata  (the  deposits  of 
previous  epochs),  continuous  and  unchanged  in  lithological  character, 
over  large  tracts  of  country.     Therefore,  in  contiguous  localities,  simi- 
larity of  lithological  character  becomes  a  very  valuable  means  of  iden- 
tifying strata.     If,  in  two  localities  not  too  widely  separated,  we  find  a 
similar  rock,  e.  g.,  a  sandstone  of  similar  grain  and  color,  we  conclude  that 
they  probably  belong  to  the  same  age,  or  are,  in  fact,  the  same  stratum. 

3.  Comparison  of  Fossils. — This  is  by  far  the  best,  and  in  widely- 
separated  localities  the  only,  method  of  determining  the  age  of  rocks. 
The  principle  of  this  method  is  that  every  geological  epoch  has  its  own 
fauna  and  flora  with  many  characteristic  forms,  by  which  it  may  be 
identified  everywhere  in  spite  of  those  slight  differences  which  result 
from  geographical  diversity ;  and,  therefore,  similarity  of  fossils  shows 
similarity  of  age.     There  are,  however,  certain  limitations  to  the  appli- 
cation of  this  method  which  must  be  borne  in  mind : 

(a.)  The  lower  marine  species  are  much  affected  by  depths  and  bot- 
toms, and  therefore  we  should  expect  that  sandstone  fossils,  limestone 
fossils,  and  slate  fossils,  would  differ  in  species  even  in  the  same  epoch. 
Again,  in  lake  and  delta  deposits,  the  entombed  species  would  probably 
be  entirely  different  from  those  of  marine  deposits.  We  must  be  care- 
ful, therefore,  to  compare  fossils  of  rocks  formed  under  similar  conditions. 


CLASSIFICATION   OF  STRATIFIED   ROCKS. 


199 


(b.)  We  must  also  make  due  allowance  for  geographical  diversity. 
This,  as  we  have  already  stated,  becomes  greater  and  greater  as  we 
pass  up  the  series  of  rocks.  In  the  lower  or  older  rocks  the  geographi- 
cal diversity  is  small ;  in  strata  of  the  same  age  in  different  countries 
the  fossils  are  quite  similar,  most  of  the  genera  and  many  of  the  species 
being  undistinguishable.  It  is  therefore  comparatively  easy,  by  com- 
parison of  fossils,  to  synchronize  the  strata  and  determine  the  geologi- 
cal horizon.  In  the  middle  rocks  the  geographical  diversity  is  greater, 
but  the  general  similarity  is  still  considerable — the  difference  between 
organisms  of  consecutive  epochs  (geological  faunas  and  floras)  is  still 
much  greater  than  the  difference  between  organisms  of  the  same  epoch 
in  different  countries  (geographical  faunas  and  floras) ;  and,  therefore, 
it  is  still  quite  possible,  by  comparison  of  fossils,  to  synchronize  the 
strata.  In  the  higher  or  newer  rocks  the  geographical  diversity  has 
become  so  great  that  we  are  compelled  to  determine  age  and  synchronize 
strata,  no  longer  entirely  by  comparison  of  fossils  of  the  different  localities 
with  each  other,  but  also  by  the  comparison  of  the  fossils  of  each  local- 
ity with  the  living  species  in  the  same  locality.  In  these  rocks  we  may 
also  determine  relative  age  by  relative  percentage  of  living  species,  and 
similarity  of  age  (geological  horizon)  by  similarity  of  this  percentage. 

Manner  of  constructing  a  Geological  Chronology.— The  manner  LQ 
which  a  geological  chronology  has  actually  grown  up,  under  the  com- 
bined labors  of  the  geologists  of  all  countries,  may  be  briefly  stated  as 
follows :  First,  the  order  of  superposition,  and  therefore  the  relative 
ages  of  the  strata  composing  the  rock-series  of  many  different  countries, 
were  determined  independently ;  next,  by  comparison  of  these,  partly 
by  lithological  character,  if  the  localities  are  contiguous,  and  partly  by 
fossils,  the  geologist  determines  those  which  are  synchronous  and  those 
which  are  wanting 
in  each  locality.  A 
Thus,  out  of  several 
local  series,  by  in- 
tercalation, he  con- 
structs a  more  com- 
plete ideal  series. 
In  case  of  doubt,  he 
strives  to  find  places 
where  the -doubtful 
strata  come  togeth- 
er, and  observes  their  relative  position.  In  Fig.  179,  A  and  B  rep- 
resent two  contiguous  localities  in  which  by  independent  study  the  rela- 
tive positions  and  ages  of  6  and  7  strata  respectively  have  been  deter- 
mined. By  comparison,  the  rocks  of  the  two  series  are  found  to  con- 
sist of  eleven  strata  of  different  ages,  some  .being  wanting  in  the  one 


1  = 


Fl°-  l?9.-Diagram  illutating 


200 


STRATIFIED   OR   SEDIMENTARY   ROCKS. 


and  some  in  the  other  locality.  The  figure  represents  the  strata  as  con- 
nected and  traceable  from  one  locality  to  the  other,  but  the  intervening 
portions  between  A  and  B  may  be  removed  by  erosion,  as  shown  by  the 
dotted  line,  or  covered  with  water.  In  such  case,  the  actual  overlap- 
ping can  not  be  observed,  if  it  ever  existed,  but  the  comparison  in  other 
respects  is  the  same.  In  widely-separated  localities  of  course  the  com- 
parison can  only  be  made  by  means  of  fossils.  Thus  as  the  examina- 
tion of  the  earth's  surface  progresses,  with  every  new  country  examined 
some  gaps  are  filled  up,  and  the  series  becomes  more  perfect.  Many 
gaps  still  remain  unfilled.  The  series  will  continue  to  be  made  more 
perfect,  and  the  chronology  more  complete,  until  the  geological  exami- 
nation of  the  earth-surface  is  finished. 

The  second  object  to  be  attained  by  classification  is  the  division  and 
subdivision  of  the  whole  series  into  larger  and  smaller  groups,  corre- 
sponding to  the  eras,  periods,  and  epochs  of  time. 

The  following  is  an  outline  of  the  classification  of  Dana,  slightly 
modified.  Except  in  the  uppermost  part  it  is  carried  only  as  far  as 
periods : 


ERAS. 

AGES. 

PERIODS. 

EPOCHS. 

5.  Psychozoic. 

7.  Age  of  Man. 

Human, 

23        Recent. 

4.  Cenozoic. 

6.  The  Age  of  Mam- 
mals. 

f  Quaternary, 
[Tertiary, 

Terrace. 
22        Champlain. 
Glacial. 
Pliocene. 
21     •  Miocene. 
Eocene. 

3.  Mesozoic. 

5.  The  Age    of    Rep- 
tiles. 

(  Cretaceous, 
•<  Jurassic, 
(  Triassic, 

20 
19 
18 

2.  Palaeozoic. 

Carboniferous  Age.  ( 
4.  The  Age  of  Aero-  I 
gens    and   Am-] 
phibians. 

(  Permian, 
•<  Carboniferous, 
(  Sub-carboniferous, 

17 
16 
15 

Devonian. 
3.  The  Age  of  Fishes. 

(  Catskill, 
Chemung, 
I  Hamilton, 
Corniferous, 
[_  Oriskany, 

14 
13 
12 
11 
10 

Silurian. 
2.  The  Age  of  Inverte- 
brates. 

Helderberg, 
Salina, 
Niagara, 
-  Trenton, 
Canadian, 
Potsdam, 
[  Acadian, 

9 
8 
7 
6 
5 
4 
3 

1.  Archaean,  or 
Eozoic. 

1.  Archaean. 

j  Huronian, 
\  Laurentian, 

2 

1 

CLASSIFICATION   OF  STRATIFIED   ROCKS.  201 

As  we  have  already  stated,  the  gaps  in  the  series  are  usually  indi- 
cated by  unconformity.  Now,  since  unconformity  always  indicates 
movements  of  the  crust,  changes  of  the  outlines  of  sea  and  land, 
changes  of  climate,  and  consequent  changes  in  the  fauna  and  flora, 
these  gaps  mark  the  times  of  great  revolutions  in  the  earth's  history, 
and  are  therefore  the  natural  boundaries  of  the  eras,  periods,  etc.  The 
whole  rock-series,  therefore,  is  divided,  by  means  of  unconformity  and 
the  character  of  the  fossils,  into  larger  groups  called  systems,  and  these 
again  into  smaller  groups  called  series  and  formations.  The  largest 
groups  are  founded  upon  universal,  or  almost  universal,  unconformity, 
and  a  consequent  very  great  difference  in  character  of  organisms ;  the 
smaller  groups  are  founded  upon  a  less  general  unconformity  and  less 
difference  in  character  of  the  organisms.  Corresponding  with  the  great 
divisions  and  subdivisions  of  the  rock-system  are  the  eras,  ages, periods, 
and  epochs  of  the  history.  The  several  terms  expressing  the  divisions 
and  subdivisions,  both  of  the  rocks  and  of  the  history,  are  unfortu- 
nately used  in  a  loose  manner.  We  will  try  to  use  them  in  the  manner 
indicated.  It  will  be  observed  that  the  divisions  are  founded  upon  (a) 
unconformity,  and  (b)  change  in  fossils.  These  generally  accompany 
each  other,  since  they  are  produced  by  the  same  cause,  viz.,  change  of 
physical  geography.  In  some  localities,  however,  they  may  be  in  dis- 
cordance. In  this  case,  the  change  of  fossils  is  considered  the  more 
important,  and  controls  classification. 


CHAPTER  III. 
UNSTRATIFIED   OR  IGNEOUS  ROCKS. 

Characteristics. — The  unstratified  are  distinguished  from  the  strati- 
fied rocks,  a,  by  the  absence  of  true  Stratification — i.  e.,  lamination  of 
sorted  materials ;  b,  by  absence  of  fossils ;  c,  by  a  more  or  less  crystal- 
line or  else  a  glassy  structure ;  and,  d,  by  their  mode  of  occurrence  ex- 
plained below. 

General  Origin, — They  have  consolidated  from  a  fused  or  semi-fused 
condition,  and  are,  therefore,  called  igneous  rocks.  This  origin  is 
shown  by  their  structure ;  by  their  occurrence  in  dikes  and  tortuous 
veins ;  by  their  effects  on  stratified  rocks  with  which  they  come  in  con- 
tact ;  and  by  their  resemblance  in  many  cases  to  modern  lavas.  The 
question  of  their  probable  mode  of  origin  will  be  more  specifically 
treated  after  the  description  of  their  kinds. 

Mode  of  Occurrence. — Igneous  rocks  occur,  a,  underlying  the  strata, 
and  forming  the  great  mass  of  the  earth's  interior ;  a',  forming  the 


202 


UNSTRATIFIED   OR  IGNEOUS   ROCKS. 


axes  and  peaks  of  nearly  all  great  mountain-ranges ;  W ',  in  vertical  or 
nearly  vertical  sheets,  filling  great  fissures  in  stratified  or  in  other 
igneous  rocks ;  c,  in  extensive  horizontal  sheets  overlying  the  stratified 
country  rock,  as  if  outpoured  on  the  surface ;  d,  lying  conformably 
between  strata,  as  if  forced  in  a  melted  condition  between  them,  or  else 


ranitice. 
|~^|  Metamorphic. 

Palaeozoic. 
E>':>|Mesozoic. 

Cenozoic. 


FIG.  180.—  Diagram  showing  Mode  of  Occurrence  of  Igneous  Rocks. 


outpoured  on  the  bed  of  the  sea  and  afterward  covered  with  sediment  ; 
and,  d,  in  tortuous  veins  connected  with  the  great  underlying  masses. 
All  these  positions  are  illustrated  in  Fig.  180.  In  all  these  modes  of 
occurrence  the  observed  rock  is  connected  with  an  underlying  mass, 
of  which  it  is  but  an  extension. 

Extent  on  the  Surface.  —  The  appearance  of  these  rocks  on  the  sur- 
face is  far  less  extensive  than  that  of  the  stratified  rocks.  Certainly 
not  more  than  one  tenth  of  the  land-surface  is  composed  of  them. 
But,  beneath,  they  are  supposed  to  constitute  the  great  mass  of  the 
earth. 

Classification  of  Igneous  Rocks.  —  Igneous  rocks  are  best  classified, 
not  by  means  of  their  relative  ages,  but  partly  by  their  mineralogical 
character  and  partly  by  their  mode  of  occurrence.  By  this  method 
they  most  naturally  fall  into  two  primary  groups  —  viz.,  the  Plutonic 
or  massive,  and  the  volcanic,  or  true  eruptive  rocks.  The  rocks  of  the 
first  group  occur  in  great  masses  ;  those  of  the  second  group  injected 
into  fissures  or  outpoured  on  the  surface.  The  former  are  entirely 
crystalline  (holo-crystalline),  and  usually  very  coarse-grained  (macro- 
crystalline) ;  the  latter  are  usually  finer  grained  (micro-crystalline),  or 
imperfectly  crystalline  (crypto-crystalline),  or  partly  or  even  wholly 
glassy.  The  former  seem  to  have  solidified  in  situ  (indigenous)  ;  the 
latter  have  been  evidently  displaced  form  their  original  position  (exot- 
ic). The  two  groups,  however,  pass  by  insensible  gradations  into  each 
other,  so  that  the  distinction  is  more  or  less  artificial,  and  the  same 
rock  may  sometimes  be  found  in  both  groups. 


PLUTONIC   OR   MASSIVE   ROCKS. 


203 


1.—  PLUTONIC  OR  MASSIVE  ROCKS. 

General  Appearance.  —  The  rocks  of  this  group  are  characterized  by 
a  coarse-grained,  mottled,  or  speckled  appearance,  arising  from  the 
fact  that  they  are  composed  of  an  aggregation  of  distinct  crystals  of 
different  colors  and  of  considerable  size  (macro-crystalline)  ;  and,  what 
is  much  more  important,  the  rock  is  usually  wholly  made  up  of  an  ag- 
gregation of  such  crystals,  without  any  paste  or  ground-mass,  either 
amorphous  or  glassy,  between  them. 

The  constituent  minerals  of  this  group  are  mainly  quartz,  feldspar, 
mica,  and  hornblende.  In  the  speckled  mass  the  opaque,  white,  or  red- 
dish or  greenish  crystals  with  glistening  surface  are  feldspar,  the  trans- 
parent bluish  glassy  spots  are  quartz,  <aud  the  black  specks  are  usually 
hornblende.  The  mica  can  be  easily  detected  as  glistening  scales  of 
various  shades. 

Principal  Kinds  —  Granite.  —  This  rock,  which  may  be  regarded  as 
the  type  of  the  group,  consists  of  quartz,  feldspar,  and  mica,  or  else  of 
these,  together  with  horn- 
blende.  Sometimes  the 

mica  and  hornblende  are 

,  .  , 
wanting,  and   the  quartz 

exists  in  the  form  of  bent 
plates  imbedded  in  feld- 
spar, so  that  on  cross- 
section  they  look  like  He- 

brew Or  Arabic  characters 

(  Fig.  181,  A  and  B).  The 
rock  is  then  called  graphic  granite,  or  pegmatite.  Sometimes  the  feld- 
spar is  in  large,  well-formed  crystals  in  a  finer  but  still  crystalline 
ground-mass:  then  it  is  called  porphyrltic  granite.  Sometimes  all 
the  crystals  are  small,  and  the  mass  is  evenly  granular  ;  then  it  is  called 
eurite,  or  granulite. 

Syenite.  —  English  and  many  American  writers  use  this  term  to 
designate  a  granitic  rock  in  which  mica  is  replaced  by  hornblende  ; 
and,  when  both  hornblende  and  mica  are  present,  they  use  the  term 
xyenitic  granite.  But  on  the  Continent  of  Europe  the  term  syenite  is 
applied  to  a  rock  consisting  essentially  of  feldspar  and  hornblende, 
and  when,  in  addition,  quartz  is  present  (English  syenite),  they  call 
the  rock  quartz-syenite.  The  general  aspect  of  the  rock  is  similar  to 
granite. 

In  the  rocks  thus  far  mentioned  the  feldspar  is  an  or  tide,  or  pot- 
ash-feldspar (orthoclase)  —  i.  e.,  is  a  double  silicate  of  alumina  anci 
potash. 

Diorite.  —  This  is  a  dark,  speckled,  greenish-gray  rock,  consisting  of 


Flo<  Ml.—  Graphic  Granite:^,  cross-section;  B,  longitudin- 


204  UNSTRATIFIED   OR  IGNEOUS  ROCKS. 

a  crystalline  aggregate  of  clinic  or  soda-lime  feldspar  (plagioclase),  and 
hornblende;  and,  therefore,  differs  from  syenite  of  German  writers 
only  in  the  form  of  the  feldspar — viz.,  plagioclase  instead  of  orthoclase. 
When  quartz  is  present  it  is  called  quartz-diorite. 

Diabase, — This  is  a  .dark,  greenish  crystalline  rock,  usually  fine- 
grained, but  sometimes  granitoid,  somewhat  similar  in  appearance  to 
diorite,  but  differing  in  the  fact  that  augite  replaces  hornblende.  It 
also  often  contains  olivin.  Gabbrvis  a  granitoid  variety  of  diabase,  in 
which  the  augite  takes  the  form  of  diallage. 

We  have  selected  these  as  good  types  of  the  groups  ;  but  they  merge 
insensibly  into  each  other,  giving  rise  to  many  varieties,  for  the  de- 
scription of  which  we  must  refer  the  reader  to  special  treatises  on 
lithology. 

Diorite  and  diabase  are  so  frequently  intrusive  and  fine-grained 
that  they  are  often  treated  in  an  intermediate  or  even  in  the  second 
group ;  but  they  also  often  occur  massive. 

Two  Sub-Groups—Acidic  and  Basic. — Quartz  is  pure  silicic  acid. 
Feldspar  is  a  silicate  of  alumina  and  alkali,  with  excess  of  silica — i.  e., 
an  acid  silicate  of  these  bases.  In  orthoclase  the  alkali  is  potash ;  in 
plagioclase,  soda  and  lime.  Moreover,  the  former  is  more  acid  than 
the  latter.  Hornblende  and  augite  are  basic  silicates  of  somewhat 
similar  composition.  Augite  is  essentially  a  silicate  of  magnesia  and 
iron ;  while,  in  hornblende,  alumina  and  lime  replace  a  portion  of  the 
magnesia.  Eemembering,  further,  that  quartz  and  feldspar  are  light- 
colored  minerals,  with  specific  gravity  of  about  2-6,  while  augite  and 
hornblende  are  usually  black  minerals,  with  specific  gravity  of  3  to  3'5, 
it  is  plain  that  this  group  of  rocks  may  be  divided  into  two  sub-groups, 
acidic  and  basic,  often  recognizable  to  the  eye.  In  the  one  there  is  a 
predominance  of  quartz  and  feldspar,  in  the  other  of  hornblende  or 
augite.  Also,  in  the  one  the  feldspar  is  orthoclase,  in  the  other  plagi- 
oclase. The  one  is  light  colored,  of  less  specific  gravity,  'and  more 
difficultly  fusible ;  the  other  darker  colored,  heavier,  and  more  easily 
fusible.  Granite  is  the  best  type  of  the  one;  diorite,  and  especially 
diabase  or  gabbro,  of  the  other.  Syenite  is  intermediate.  The  per- 
centage of  silica,  both  free  and  combined,  in  granite  is  62  to  81,  and 
the  specific  gravity  2*6  to  2'7.  The  silica  percentage  in  diabase  is  45 
to  56,  and  the  specific  gravity  2-7  to  2-9  (Von  Cotta). 

Mode  of  Occurrence. — True  Plutonics,  especially  of  the  granitic 
type,  such  as  granite  and  syenite,  occur :  1.  In  large  masses,  forming 
the  axes  of  great  mountain-ranges,  such  as  the  Sierra  and  Colorado 
ranges  (Fig.  182,  A) ;  or,  2.  In  rounded  masses,  appearing  in  the  midst 
of  stratified  rocks  like  islands  in  the  midst  of  the  sea  (Fig.  182,  B) ;  or, 
3.  Sometimes  in  tortuous,  irregularly  branching  veins,  extending  only 
a  little  way  from  the  great  masses  into  the  overlying  stratified  rocks,  as 


INTERMEDIATE  SERIES. 


205 


if  forced  by  pressure  of  superincumbent  weight  into  small  cracks  of  the 
latter  (Fig.  180,  d,  Fig.  182,  A,  and  Fig.  183,  A  and  B).  But  rocks 
of  more  basic  type,  such  as 
diorite  and  diabase,  probably 
on  account  of  greater  fusibil- 
ity, occur  not  only  as  Pluton- 
ics  in  massive  form,  but  also 
as  intrusives  in  dikes  and  in- 


tercalary  beds,  like  true  vol- 

canics.  ^^^"v    "v     ^      ^  ^^ 

The  rocks  of  the  Plutonic 

group  are  never  found  in 
connection  with  scoriae,  glass,  ashes,  or  other  evidences  of  rapid  cooling 
in  contact  with  air.  They  have  never  been  erupted  on  the  surface. 
They  were  cooled,  and  have  solidified  slowly  under  pressure  in  great 


FIG. 


.—  Diagram  illustrating  Mode  of  Occurrence  of 
Granite. 


FIG.  m— Granite  Veins. 


masses  and  at  great  depths.  Hence,  when  we  find  them  at  the  surface, 
they  have  been  exposed  by  extensive  erosion.  They  are  either  fused 
masses  solidified  without  eruption  («),  or  they  are  the  solidified  reser- 
voirs (g,  Fig.  180)  from  which  eruptions  have  come.  In  either  case, 
they  have  themselves  been  cooled  at  great  depths. 

Intermediate  Series. 

Between  the  undoubted  Plu tonics,  already  described,  and  the  un- 
doubted volcanics,  to  be  taken  up  hereafter,  there  is  an  intermediate 
series  of  rocks,  which  are  sometimes  placed  in  one  group,  sometimes  in 
the  other,  and  sometimes  in  a  separate  group,  co-ordinate  with  the  other 
two,  and  called  trappean  or  intrusive  rocks.  They  occur  mostly  in  the 
older  and  middle  rocks  in  the  form  of  dikes,  filling  great  fissures  inter- 
secting, or  as  intercalary  beds  between,  the  strata.  If  Plutonics  are 
in  great  masses  beneath  the  strata,  and  volcanics  are  outpoured  masses 


206  UNSTRATIFIED   OR   IGNEOUS   ROCKS. 

upon  the  strata,  these  exist  mostly  as  masses  intruded  among  the 
strata.  Again,  if  Plutonics  are  the  great  reservoirs  and  volcanics  the 
outpoured  liquid,  the  intrusives  are  the  fillings  of  the  conduits  between. 
Erosion  has  subsequently  carried  'away  the  overflowed  portions,  and 
exposed  the  conduits  as  dikes. 

Kinds. — In  the  acidic  groups,  perhaps  the  most  typical  is  felsite. 
This  rock  is  a  very  compact,  fine-grained  aggregate  of  quartz  and 
orthoclase,  and  therefore  light-colored.  Chemically  it  has  the  same 
composition  as  granite,  and  mineralogically  it  differs  only  in  the  fine- 
ness of  texture  and  in  the  absence  of  mica.  When  the  felsitic  rock 
contains,  imbedded  in  the  fine-grained  mass,  large,  well-formed  crystals 
of  feldspar,  then  it  is  called  porpliyrite.  If  quartz-crystals  are  also 
distinctly  visible,  then  it  is  called  quartz-porphyry,  or  elvanite,  a 
mottled  rock  often  mistaken  for  granite.  The  word  porphyritic  is 
often  applied  to  any  rock  in  which  distinct  crystals  are  visible  in  a 
finer  ground-mass.  Thus,  we  have  porphyritic  granite,  porphyritic 
diorite,  etc.  The  porphyritic  structure  is  probably  formed  thus  :  The 
fused  magma  first  cooled  slowly  until  the  large  crystals  separated ;  and 
then  was  injected  into  the  fissure  and  the  solidification  completed. 

Intrusive  rocks  of  the  basic  sub-group  are  usually  called  green- 
stones or  traps.  This  term,  therefore,  includes  intrusive  diorites,  dia- 
bases, aphanites,  melaphyrs,  etc.  These  differ  from  the  massive  rocks 
of  the  same  composition  only  by  being  finer  grained  :  but  the  same  is 
true  also  of  felsites  as  compared  with  granites.  The  difference  is  prob- 
ably wholly  due  to  rate  of  cooling.  The  same  fused  mass  which,  if 
cooled  slowly,  forms  granite,  if  injected  into  fissures  and  cooled  more 
rapidly,  would  form  felsite  or  quartz-porphyrite.  The  difference  be- 
tween massive  and  intrusive  diorites  is  doubtless  due  to  the  same  cause. 

II. — VOLCANIC  OR  ERUPTIVE  EOCKS. 

Texture  and  Appearance.— The  rocks  of  this  group  are  usually 
micro-crystalline,  or  even  crypto-crystalline,  and  therefore  in  appear- 
ance are  either  minutely  speckled  or  evenly  grayish,  of  various  shades. 
But  the  most  important  characteristic  is,  that  they  are  not  wholly  crys- 
talline, but  consist  either  of  crystals  imbedded  in  an  amorphous  or 
glassy  paste,  or  else  are  wholly  amorphous  or  'glassy.  This  texture 
shows  that,  as  compared  with  the  rocks  of  the  other  groups,  they  have 
cooled  quickly,  for,  on  account  of  the  extreme  viscosity  of  fused  sili- 
cates (glass),  complete  crystallization  can  take  place  only  by  very  slow 
cooling. 

Physical  Conditions, — All  the  physical  conditions  already  described 
(p.  91)  as  characteristic  of  recent  lavas,  viz.,  the  stony,  the  glassy,  the 
scoriaceous,  and  the  tufaceous  conditions,  are  found  abundantly  in 'the 
more  typical  representations  of  this  group. 


VOLCANIC  OR  ERUPTIVE  ROCKS. 


207 


Mineral  Composition  and  Sub-Groups. — The  most  striking  differences 
between  the  rocks  of  this  and  the  other  groups  are  found  in  their  text- 
ure and  mode  of  occurrence.  Mineralogically  the  rocks  of  this  group 
consist  essentially  of  some  form  of  feldspar,  with  hornblende  or  augite. 
Free  quartz  and  mica,  though  sometimes  present,  especially  the  former, 
are  neither  necessary  nor  common.  These  also,  like  those  of  the  other 
group,  may  be  divided  into  two  sub-groups,  acidic  and  basic.  In  the 
one  there  is  a  predominance  of  orthic  feldspar  (sanidin) ;  in  the  other, 
of  either  hornblende  or  augite  and  clinic  feldspar  (plagioclase).  In 
true  volcanics,  as  seen  above,  sanidin  takes  the  place  of  orthoclase  of 
the  Plutonics.  These,  however,  belong  to  the  same  group  (orthoclase 
group),  are  equally  acidic,  and,  therefore  have  the  same  significance  in 
lithology.  The  two  sub-groups  are,  therefore,  characterized  by  color, 
specific  gravity,  and  fusibility,  as  already  explained  (p.  204),  and,  with 
some  practice,  can  usually  be  distinguished  in  the  field;  though  in 
many  cases  microscopic  or  chemical  examination  is  necessary.  The 
silica  percentage  of  the  extreme  acidic  type  (rhyolite)  is  70  to  82,  and 
specific  gravity  2-3  to  2-6  ;  of  the  extreme  basic  (basalt)  the  silica  per- 
centage is  40  to  56,  and  specific  gravity  2-9  to  3*1.  The  following 
schedule  gives  the  most  common  and  characteristic  kinds  under  the 
two  sub-groups: 


VOLCANIC  ROCKS. 

ACIDIC. 

BASIC. 

f  Rhyolite. 

Basalt. 

Stony 
condition. 

I  Liparite. 
j  Trachyte. 

Dolerite. 
Andesite. 

^  Phonolitc. 

Propylite 

Glassy 
condition. 

(  Light-colored  scoriae. 
•J  Pumice.  • 
(  Obsidian.  J 

Black  scoriae. 
Tachylite. 

Principal  Kinds. — In  the  acidic  group  the  commonest  and  best  type 
is  trachyte.  This  is  usually  a  light-colored  rock,  with  a  peculiar  and 
very  characteristic  rough  feel,  due  to  microscopic  vesicularity.  It 
consists  essentially  of  a  ground-mass  of  orthic  feldspar  (sanidin)  and 
augite,  containing  crystals  of  the  former. 

Rhyolite  is  similar  in  composition  to  trachyte,  but  contains  a  larger 
percentage  of  silica,  and  is  very  different  in  general  appearance.  It 
consists  of  a  fluent,  vitreous  ground-mass  or  paste,  usually  containing 
crystals  of  sanidin,  or  even  of  quartz.  When  these  crystals  are  con- 
spicuous, so  that  the  rock  has  a  porphyritic  appearance,  it  is  called 
liparite.  In  some  cases  it  may  have  even  a  granitoid  appearance,  and 


208 


UNSTRATIFIED   OR  IGNEOUS  ROCKS. 


is  then  called  nevadite.  Such  granitoid  rhyolite  may  be  easily  distin- 
guished from  true  granite  by  the  presence  of  the  glassy  paste. 

Phonolite  is  a  light-grayish  crypto- crystalline  feldspathic  rock, 
breaking  or  jointing  in  very  characteristic  thin  tile-like  slabs,  which 
ring  under  the  hammer  (hence  the  name).  It  consists  mainly  of  orthic 
feldspar  (sanidin  and  nephelin).  ^ 

In  the  basic  sub-group  the  most  common  and  typical  is  oasalt. 
This  is  a  very  dark,  almost  black,  crypto-crystalline  rock,  breaking 
with  a  dull,  conchoidal  fracture,  and  consisting  essentially  of  micro- 
scopic crystals  of  plagioclase,  augite,  and  olivin,  in  a  glassy  ground-mass 
of  the  same.  Magnetite  is  also  usually  an  abundant  constituent.  Dol- 
erite  has  a  somewhat  similar  composition,  but  lacks  the  olivin,  and  is 
more  crystalline  in  structure,  and  therefore  dark-grayish  in  appearance. 
Andesite  is  a  dark-grayish  rock,  consisting  essentially  of  plagioclase, 
with  hornblende  or  augite.  It  is  somewhat  similar  in  color  to  dolerite, 
but  is  crypto-crystalline,  like  basalt,  and  often  roughish  to  the  feel, 
like  trachyte.  It  has,  therefore,  been  sometimes  called  trachy-dolerite. 

All  the  rocks  of  both  these  sub-groups,  but  especially  the  more 
typical,  have  their  scoriaceous  and  glassy  varieties.  These  are  the 
pumices  and  light-colored  scoriae  and  obsidians  on  the  one  hand,  and 
the  black  scoriae  and  tachylite  on  the  other. 

The  following  table  is  a  condensed  statement  of  the  composition 
of  the  principal  kinds  in  both  primary  groups,  including  also  intrusives. 
The  sign  x  x  indicates  crystals  : 


IGNEOUS  KOCKS. 


ACIDIC. 

BASIC. 

II.  VOLCANIC 
EOCKS. 

Occurring  in 
overflows. 

RJiyolite.             Trachyte. 
Vitreous               Vitreous 
ground-mass.        ground-mass. 

Phonolite. 
Vitreous 
ground-mass. 

I  Sanidin, 
x  }  Nephelin. 

Andesite. 
Vitreous 
ground  -mass. 

(  Plagioclase, 
x  x  •<  Augite,  or 
(  Hornblende 

Basalt. 
Vitreous 
ground-mass. 

{Plagioclase, 
Augite, 
Olivin. 

ill 

Quartz-porphyry. 
Micro  x  x  ground  -mass.                     FeMte. 

(  Orthoclase,                Micro  j  Orthoclase,   < 
x  1  Quartz,                        x  x    \  Quartz. 

Z>ioHte. 
Same  as 
below, 
but  micro 
x  x 

Diabase. 
Same  as 
below, 
but  micro 
x  x 

I!{(! 

Granite. 
(  Quartz. 
x  x  -{  Orthoclase,                    x  x 
1  Mica. 

Syenite. 

(  Orthoclase. 
|  Hornblende. 

Diorite. 
v  j  Plagioclase. 
x  \  Hornblende 

Gabbro. 
(  Plagioclase, 
x  x  •<  Augite, 
/  Olivfn. 

Modes  of  Eruption. — There  have  been  in  geological  times  two  gen- 
eral modes  of  eruption.     In  the  one  the  lavas  have  come  up  through 


VOLCANIC   OR   ERUPTIVE   ROCKS. 


209 


great  fissures  formed  by  crust-movements  and  spread  out  as  extensive 
sheets  ;  in  the  other  they  have  come  up  through  chimneys  and  run  off 
as  streams.  The  one  may  be  called  fissure-eruption,  the  other  crater- 
eruption  or  volcanoes  proper.  The  one  gives  rise  to  extensive  lava- 
fields,  the  other  to  lava-cones.  The  force  of  eruption  in  the  one  case 
is  probably  either  the  same  as  that  which  makes  mountains — i.  e.,  the 
lava  is  squeezed  out  by  interior  contraction  of  the  earth,  or  else,  in 
some  cases  it  may  be  hydrostatic — i.  e.,  a  welling  out  of  a  lighter  liquid 
by  the  sinking  of  a  heavier  crust  within  it ;  the  force,  in  the  other  case, 
is  evidently  the  pressure  of  elastic  gases,  especially  steam,  as  already 
explained  (p.  97).  We  owe  this  distinction  mainly  to  Richthofen,  but 
it  is  now  universally  adopted  in  this  country  and  quite  generally  in 
Europe.  According  to  Richthofen,  primary  eruptions  come  always 
through  great  fissures  and  only  at  great  intervals  of  time;  afterward, 
surface-waters  percolating  through  these  fissure-erupted  masses,  still 
liquid  within,  give  rise  to  secondary  eruptions  through  craters.  We 
have  no  examples  of  fissure-eruptions  taking  place  at  the  present  time, 
and  therefore,  in  treating  of  igneous  agencies  in  Part  I,  we  spoke  only 
of  crater-eruptions.  But  it  is  impossible  to  explain  the  mode  of  occur- 
rence of  eruptives  in  the  older  rocks  unless  we  admit  eruptions  in  early 
geological  times  of  a  different  kind  from  those  occurring  now  in  vol- 
canoes. 

Modes  of  Occurrence. — What  we  say  under  this  head  refers  mainly 
to  fissure-eruptions.  True  eruptive  rocks  occur :  1.  As  extensive 
vertical  sheets  filling  great  fissures  which  by  subsequent  erosion  out- 
crop as  great  dikes,  or  else  filling  smaller  radiating  volcanic  fissures 
as  radiating  volcanic  dikes ;  2.  As  sheets  between  the  strata  (interca- 
lary beds)  as  if  forced  between  the  separated  strata,  or  eke  outpoured 
on  the  bed  of  sea  or  lake,  and  again  covered  with  sediments ;  3.  Out- 
poured on  the  land-surface  as  sheets  or  streams ;  and,  4.  In  the  form  of 
great  dome-like  masses  on  the  surface  or  between  the  strata. 

Dikes. — The  fillings  of  great  fissures  outcropping  on  land-surfaces 
are  called  dikes.  They  are  very  abundant  in  all  the  older  stratified 
rocks,  especially  in  mountain-re- 
gions. They  vary  in  thickness 
from  a  few  inches  to  fifty  or  one 
hundred  feet ;  they  may  be  traced 
over  the  country  sometimes  for 
many  miles,'  even  fifty  or  one 
hundred,  and  extend  downward 
to  great  but  unknown  depths. 
Such  dikes,  outcropping  over  the  face  of  the  country,  may  be  the  ex- 
posed roots  of  ancient  overflows  which  have  been  removed  by  subse- 
quent erosion  (Fig.  180,  b) ;  or  they  may  be  fillings  of  fissures  which 
14 


FIG.  184.— Dikes. 
\ 


210 


UNSTRATIFIED   OR   IGNEOUS  ROCKS. 


never  reached  the  surface  (Fig.  180,  V).  In  either  case  they  are  the 
evidence  of  extensive  erosion.  Sometimes  the  outcropping  dike  has 
resisted  erosion  more  than  the  inclosing  country  rock,  and  the  dike  is 
left  standing  like  a  low,  ruined  wall  running  over  the  face  of  the  coun- 
try (Fig.  184,  a) ;  at  other  times  the  country  rock  has  resisted  more 
than  the  dike,  and  the  place  of  the  dike  is  marked  by  a  slight  depres- 
sion, like  a  shallow  ditch,  or  moat  (Fig.  184,  b). 

Effect  of  Dikes  on  the  Intersected  Strata. — The  strata  forming  the 
bounding  walls  of  a  dike,  or  with  which  igneous  rocks  come  in  contact 
in  any  way,  are  almost  always  greatly  changed  by  the  intense  heat  of 
the  fused  matter.  Limestones  and  chalk  are  changed  into  crystalline 
marble;  clay  is  baked  into  porcelain-jasper,  or  even  changed  into 
schists ;  impure  sandstones  are  changed  into  a  speckled  rock  resem- 
bling gneiss ;  seams  of  bituminous  coal  are  changed  into  anthracite, 
or  sometimes  into  coke.  In  all  cases  the  original  stratification  and  the 
contained  fossils  are  more  or  less  completely  destroyed.  These  eifects 
extend  sometimes  only  a  few  feet,  sometimes  many  yards,  from  the 
dike. 

Lava-Sheets. — Dikes  outcropping  on  the  face  of  the  country,  as 
already  described,  are  doubtless  in  many  cases  the  exposed  roots  of 
ancient  overflows  which  have  been  removed  by  subsequent  erosion, 
leaving  only  the  intruded  portion.  But  in  more  recent  eruptions  the 
overflow  or  erupted  portions  still  remain.  The  fused  matter  has  evi- 
dently come  up  through  fissures  and  spread  out  as  sheets,  and  often 

sheet  after  sheet  has  been  suc- 
cessively outpoured  forming 
layer  upon  layer  (Fig.  185),  un- 
til the  whole  surface  of  the 
country  is  deeply  buried  beneath 
the  flood.  The  extent  and 
thickness  of  the  lava-fields  thus 
formed  are  almost  incredible. 
The  great  lava-flood  of  the 
Northwest  covers  Northern 
California,  Northwestern  Nevada,  the  greater-part  of  Oregon,  Wash- 
ington, and  Idaho,  and  extends  far  into  British  Columbia  and  Mon- 
tana. Its  extent  is  not  less  than  150,000  square  miles,  and  its  extreme 
thickness  where  cut  through  by  the  Columbia  Kiver  is  3,000  to  4,000 
feet.  In  another  place  seventy  miles  distant,  the  Deschutes  River 
cuts  into  the  same  lava-field,  making  a  canon  140  miles  long  and 
1,000  to  2,500  feet  deep,  and  has  not  yet  reached  bottom.  At  least 
thirty  successive  layers  may  be  counted,  one  above  the  other,  on  the 
sides  of  this  caQon.  About  a  dozen  volcanoes  overdot  this  great  sur- 
face. It  is  simply  inconceivable  that  all  this  material  came  from 


FIG.  185. — Lava-Sheets. 


VOLCANIC  OR  ERUPTIVE  ROCKS.  211 

these  volcanoes.  It  evidently  came  up  through  great  fissures  in  the 
Cascade,  Blue  Mountains,  and  Coast  Range,  and  poured  out  on  the 
surface,  flooding  the  whole  intervening  country.*  The  Deccan  lava- 
field,  described  by  the  Indian  geologists,!  is  200,000  square  miles  in 
extent,  2,000  to  6,000  feet  thick,  and  entirely  without  detectable 
volcanic  cones  from  which  the  lava  could  have  come.  These  exten- 
sive fields  are  mostly  of  basalt.  In  Utah  and  Colorado,  according  to 
King  and  Endlich,];  rhyolitic  and  trachytic  lavas  reach  a  thickness 
of  7,000  feet.  As  a  general  rule,  outpourings  of  basalt  reach  the  great- 
est extent,  but  each  sheet  is  thin,  as  if  the  basalt  had  been  superfused  ; 
while  acidic  lavas  like  trachyte  and  rhyolite  are  outpoured  in  very 
thick,  sometimes  dome-like  masses,  as  if  they  had  been  only  semi- 
fused. 

In  basaltic  lava-fields  a  remarkable  step-like  or  terrace-like  appear- 
ance is  observable.  The  country  seems  to  rise  in  successive  tables  or 
benches.  From  this  has  arisen  the  term  trap,  from  the  Swedish  word 
trappa^  a  stair.  This  configuration  is  due  to  the  abrupt  terminations 
of  the  successive  flows  (Fig.  185). 

Intercalary  Beds  and  Laccolites. — Holmes,  in  Hayden's  Report  for 
1875,*  describes  Mount  Hesperus,  Colorado,  as  wholly  composed  of 
stratified  rocks  (cretaceous),  with  intercalated  beds  of  eruptives,  as  if 
the  lava  had  forced  itself  between  the  strata.  Such  intercalary  sheets, 
which  have  been  often  observed  by  others,  probably  pass  by  insensible 
gradations  into  laccolites — a  new  form  of  occurrence  to  which  atten- 
tion was  first  drawn  by  Holmes,  but  which  has  been  elaborately  de- 
scribed by  Gilbert  ||  as  characteristic  of  the  Henry  Mountains,  and 
other  groups  in  the  Plateau  region.  In  this  case  the  liquid  matter 
seems  to  have  come  up  through  fissures  as  usual,  but,  instead  of  break- 
ing through  to  the  surface,  has  lifted  the  upper  strata  and  accumulated 
beneath  in  great  dome-like  masses  which,  in  fact,  constitute  the  bulk 
of  the  mountains  (Fig.  186).  The  strata-covered  dome  thus  formed  is 
afterward  eroded,  and  the  igneous  core  or  laccolite  is  exposed. 

According  to  Gilbert,  whether  lava  accumulates  between  the  strata 
or  outpours  on  the  surface  is  merely  a  question  of  relative  specific 
gravity.  If  the  lava  is  lighter  than  the  strata,  then  the  latter  will  sink 
and  the  lava  be  outpoured.  If,  on  the  other  hand,  the  surface  strata 
be  lighter  than  the  lava,  then  the  lava  floats  it  up  and  accumulates  be- 

*  American  Journal  of  Science,  vol.  vii,  pp.  167,  259. 

f  American  Journal  of  .Science,  vol.  xix,  p.  140,  1880.  Manual  of  Indian  Geology, 
p.  800  ct  scq. 

\  King,  Geology  of  the  Fortieth  Parallel,  vol.  i,  p.  632.  Endlich,  Hayden's  Report 
for  1876,  p.  112. 

*  Hayden's  Report  for  1875,  p.  271.' 

|  Gilbert,  Geology  of  the  Henry  Mountains. 


212 


UNSTRATIFIED   OR  IGNEOUS  ROCKS. 


FIG.  186.— Laccolite  (after  Gilbert). 


neath.  It  seems  more  prob- 
able,4 however,  -  that  it  is 
rather  a  question  of  liquid- 
ity than  of  specific  gravi- 
ty. If  the  liquidity  is  per- 
fect as  in  basalts,  then  it 
comes  to  the  surface  and 
outpours,  and  may  extend 
to  very  great  distances ; 
but,  if,  on  the  contrary 
the  lava  is  only  a  stiffly  viscous,  semi-fused  mass,  like  trachyte  andl, 
rhyolite,  it  may  lift  up  the  strata  on  its  back  in  a  dome. 

Age — how  determined.— When  two  dikes  intersect  each  other,  then, 
of  course,  the  intersecting  must  be  younger  than  the  intersected  dike. 
In  this  manner  the  relative  age  of  dikes  intersecting  the  same  region 
may  often  be  determined.  The  absolute  age  of  igneous  rocks  can  only 
be  determined  by  means  of  the  strata  with  which  they  are  associated. 
If  a  dike  is  found  intersecting  strata  of  known  age  (Z>,  Fig.  180),  the 
dike  must  be  younger  than  the  strata.  If  a  dike  (#'),  intersecting 
strata  and  outcropping  on  the  surface,  is  found  overlaid  by  other  strata 
through  which  it' does  not  break,  then  the  igneous  injection  is  younger 
than  the  former  and  older  than  the  latter.  The  series  of  events  indi- 
cated is  briefly  as  follows :  first,  the  older  series  of  sediments  has  been 
formed ;  then  fissures  formed  and  filled  by  igneous  injection ;  then 
erosion  has  carried  away  the  upper  portion  of  the  strata  and  its  in- 
cluded dike,  so  that  the  dike  outcrops  along  the  eroded  surface ;  and, 
lastly,  the  whole  has  been  submerged  and  again  covered  with  sediment. 
In  the  case  of  intercalary  beds  of  igneous  rocks,  if  the  strata  above 
and  below  are  both  metamorphosed  by  heat,  then  the  fused  matter  has 
been  forced  between  and  is  younger  than  the  strata ;  if,  however,  the 
underlying  stratum  is  changed  but  the  overlying  is  not,  then  the  igne- 
ous matter  has  been  outpoured  on  the  sea-bed  and  covered  with  sedi- 
ment, and  is,  therefore,  of  the  same  age  as  the  strata.  The  same  prin- 
ciples determine  the  age  of  sheets  and  streams.  If  sheets  are  successively 
outpoured,  one  atop  the  other,  then,  of  course,  the  order  of  superposi- 
tion determines  their  relative  age.  So,  also,  if  two  streams  run  across 
each  other,  the  overlying  is  the  younger.  In  this  way  Richthofen  and 
others  have  determined  the  order  of  succession  of  different  kinds  of 
tertiary  eruptives.  Absolute  age,  or  the  geological  time  of  eruption, 
can  only  be  determined  by  the  age  of  the  associated  strata. 

6f  Certain  Structures  found  in  many  Eruptive  Rocks. 

Columnar  Structure. — Many  kinds  of  eruptive  rock  exhibit  some- 
times a  remarkable  columnar  structure.     This  is  most  conspicuous  in 


OF  CERTAIN   STRUCTURES  FOUND  IN   MANY   ERUPTIVE   ROCKS.  213 

basalt,  probably  because  this  rock  has  been  superfused,  and  is  therefore 
sometimes  called  basaltic  structure.  Sheets  and  dikes  of  this  rock  are 
often  found  composed  wholly  of  regular  prismatic  jointed  columns, 


FIG.  187.— Columnar  Basalt,  New  South  Wales  (Dana). 

closely  fitting  together,  varying  in  size  from  a  few  inches  to  a  foot 
or  more,  and  in  length  from  several  feet  to  fifty  or  one  hundred  feet. 
When  these  columns  have  been  well  exposed  on  cliffs  by  the  action  of 
waves,  or  on  river-banks  by  the  erosive  action  of  currents,  or  even  by 
atmospheric  disintegration,  they  produce  a  very  striking  scenic  effect 
(Figs.  187,  188).  In  Europe  the  Giant's  Causeway,  on  the  coast  of 
Ireland,  and  Fingal's  Cave,  in  the  island  of  Staffa  on  the  west  coast  of 


FIG.  188.— Basaltic  Columns  on  Sedimentary  Rock,  Lake  Snperior  (after  Owen). 

Scotland,  are  conspicuous  examples.  In  the  United  States  we  have  ex- 
amples in  Mount  Holyoke,  on  the  Connecticut  River ;  in  the  Palisades 
of  the  Hudson  River ;  in  the  traps  on  the  shores  of  Lake  Superior ; 
and  especially  in  splendid  cliffs  of  the  Columbia  and  Deschutes  Rivers, 
in  Oregon. 

Direction  of  the  Columns. — The  direction  of  the  columns  is  usually 
at  right  angles  to  the  cooling  surface.     In  horizontal  sheets,  therefore, 

'  the  columns  are  vertical,  but  in  dikes  they  are  horizontal  (Fig.  189). 

1  A  dike  left  standing  above  the  general  surface  of  country  sometimes 


214:  FNSTRATIFIED  OR  IGNEOUS  ROCKS. 

presents  the  appearance  of  a  long  pile  of  cord-wood.  In  some  cases  the 
columns  are  carved  and  twisted  in  a  manner  not  easy  to  explain;  some- 
times, instead  of  columnar,  a  ball-structure  is  observed. 


-- 


FIG.  189.— Columnar  Dike,  Lake  Superior  (after  Owen). 


Cause  of  Columnar  Structure. — There  is  little  doubt  that  this 
structure  is  produced  by  contraction  in  the  act  of  cooling.  Many  sub- 
stances break  in  a  prismatic  way  in  contracting.  Masses  of  wet  starch, 
or  very  fine  mud  exposed  to  the  sun,  crack  in  this  way.  In  basalt  the 
structure  is  more  regular  than  in  any  other  known  substance.  The 
subject  of  the  cause  of  jointed  columnar  structure  has  been  very  ably 
discussed  by  Mr.  Mallet.* 

Volcanic  Conglomerate  and  Breccia. — If  a  stream  of  fused  rock, 
whether  from  a  crater  or  a  fissure,  run  down  a  stream-bed,  it  gathers 
up  the  pebbles  in  its  course,  and  after  solidification  forms  a  conglom- 
erate which  differs  from  a  true  conglomerate  (p.  171)  in  the  fact  that 
the  uniting  paste  is  igneous  instead  of  sedimentary.  In  a  similar  man- 
ner volcanic  breccias  are  formed  by  the  flowing  of  a  lava-stream  over  a 
surface  covered  with  rubble. 

The  disintegration  of  volcanic  rocks,  and  their  transportation  and 
deposit,  will  of  course  give  rise  to  aqueous  conglomerates  and  breccias 
composed  of  volcanic  materials,  which  often  are  difficult  to  distinguish 
from  true  volcanic  conglomerates  and  breccias.  These  aqueous  con- 
glomerates and  breccias  of  volcanic  material  pass  by  insensible  grada- 
tions into  tufas,  which,  as  already  explained  (p.  91),  consist  of  fine  vol- 
canic material  cemented  into  an  earthy  mass  and  often  sorted  by  water. 

*  Philosophical  Magazine,  August  and  September,  1875. 


ORIGIN  OF  IGNEOUS   ROCKS.  215 

Amygdaloid. — Still  another  structure,  very  common  in  lavas  and 
traps,  is  the  amygdaloidal.  The  rock  called  amygdaloid  (Fig.  190) 
greatly  resembles  volcanic  conglomerate, 
being  apparently  composed  of  almond- 
shaped  pebbles  in  an  igneous  paste,  but 
is  formed  in  a  wholly  different  way. 
Outpoured  traps,  and  especially  lava- 
streams,  are  very  often  vesicular — i.  e., 
filled  with  vapor-blebs,  usually  of  a  flat- 
tened, ellipsoidal  form.  In  the  course  of 
time  these  cavities  are  filled  with  silica, 
carbonate  of  lime,  or  some  other  mate- 
rial, by  infiltrated  water  holding  these 
matters  in  solution.  Sometimes  the  fill- 
ing has  taken  place  very  slowly  by  sue- 
cessive  additions  of  different-colored  ma- 
terial. Thus  are  formed  the  beautiful  agate  pebbles,  or  more  properly 
amygduleSj  so  common  in  trap.  The  most  common  filling  is  silica, 
because  water  percolating  through  igneous  rocks  is  always  alkaline, 
and  holds  silica  in  solution. 

SOME  IMPORTANT  GENERAL  QUESTIONS  CONNECTED  WITH  IGNEOUS 

ROCKS. 

1.  Origin  of  Igneous  Rocks. 

There  are  many  reasons  for  thinking  that  igneous  rocks  are  not 
erupted  portions  of  an  original  fused  magma,  but  are  usually  the  result 
of  refusion  of  stratified  rocks.  This  question  has  been  already  touched 
in  treating  of  volcanoes  (p.  100),  but  we  are  now  in  condition  to  take  it 
up  more  fully. 

If  the  earth  cooled  from  a  primal  incandescent,  fused  condition,  it  is 
evident  that  there  would  be  substantial  homogeneity  in  any  given  layer, 
at  least  in  any  given  locality.  Erupted  matters,  therefore,  although 
they  might  indeed  slowly  change  in  composition  in  the  course  of  geo- 
logical ages,  as  deeper  and  deeper  layers  were  successively  reached  by  the 
gradual  thickening  of  the  earth's  crust,  yet,  in  the  same  locality,  and 
erupted  about  the  same  time,  they  ought  to  have  the  same  composition. 
But  we  find,  on  the  contrary,  lavas  of  the  greatest  differences — e.  g., 
rhyolite  and  basalt,  erupted  in  the  same  region,  and  nearly  at  the  same 
time.  They  can  not,  therefore,  be  portions  of  the  same  original  magma. 

Now,  in  the  primal  solidification  of  the  earth  from  fusion,  the  first 
crust  was  doubtless  a  homogeneous  igneous  rock,  somewhat  similar  in 
composition  to  diorite  or  syenite.  The  effect  of  aqueous  agencies  on 
this  original  homogeneous  material,  by  disintegration,  transportation, 


216 


UNSTRATIFIED   OR   IGNEOUS   ROCKS. 


sorting,  and  deposit,  throughout  all  geological  times,  has  been  to  pro- 
duce extreme  differentiation  of  stratified  rocks,  belonging  to  the  same 
time  and  in  the  same  region.  Hence,  if  eruptives  are  produced  by  re- 
fusion  of  these,  we  would  expect  to  find  great  diversity  among  them. 

But,  on  the  other  hand,  the  extreme  diversity  which  we  find  among 
stratified  rocks,  viz.,  pure  sandstones  (acid),  on  the  one  hand,  and  pure 
limestones  (base)  on  the  other,  is  not  found  among  igneous  rocks.  But 
this,  which  seems  at  first  an  objection,  is  found,  on  examination,  a  con- 
firmation of  our  conclusion ;  for  these  extremes  are  very  difficult  of  fu- 
sion. Thus  the  diversity  of  composition  of  igneous  rocks  is  completely 
explained  by  supposing  them  formed  by  refusion  of  stratified  rocks 
within  the  limits  of  ready  fusibility* 

2.  Other  Modes  of  Classification. 

There  is  no  subject  connected  with  geology  which  is  in  a  state  of 
greater  confusion  than  the  classification  and  nomenclature  of  igneous 
rocks.  It  seems  proper,  therefore,  to  mention  some  of  the  different 
views  entertained. 

Many  geologists  think  that  igneous  rocks  may  be  thrown  into  three 
groups,  characteristic  of  different  periods  of  the  earth's  history,  and 
which,  therefore,  are  now  found  associated  with  the  stratified  rocks  of 
different  ages.  These  are :  1.  The  granitic  group,  including  granites 
and  syenites,  associated  with  archaean  and  palaeozoic  rocks;  2.  The 
trappean  group,  including  diorites,  porphyry,  dolerite,  etc.,  associated 

with  the  later  palaeozoic  and  the  mesozoic 
rocks ;  and,  3.  The  volcanic  rocks,  including 
basalts,  trachytes,  etc.,  associated  with  the 
tertiary  rocks.  They  think,  therefore,  that 
the  earliest  eruptions  were  granitic,  then 
trappean,  and  lastly  volcanic.  Furthermore, 
they  think  that  the  first  have  come  up  most- 
ly in  great,  dome-like  masses ;  the  second, 
mostly  intrusive,  in  dikes  and  fissures ;  and 
the  third  through  craters  forming  volcanoes. 
Again,  many  think  that  erupted  matters, 
of  different  times,  have  become  progressively 
more  basic.  They  think  that,  although  each 
group  may  be  divided  into  a  more  acidic  and 
a  more  basic  sub-group,  yet,  as  a  whole,  the 
granitic  group  is  the  most  acidic  and  the 
volcanic  the  most  basic,  the  trappean  being  intermediate,  as  shown  in 
the  accompanying  diagram. 


BASIC. 


Acidic. 


Basic. 


Volcanic. 


Trachyte. 


Basalt. 


Trappean. 


Porphyry. 


Diorite. 


Granitic. 


Granite. 


Syenite. 


ACID. 


Captain  Button,  High  Plateaus  of  Utah,  p.  120. 


OTHER   MODES   OF  CLASSIFICATION.  217 

Again,  these  two  views,  which  are  usually  held  by  the  same  persons, 
are  by  them  connected  with  a  third  view,  in  regard  to  the  original  con- 
stitution of  the  earth's  crust.  On  first  cooling,  the  outer  layer  is  sup- 
posed to  have  been  highly  oxidized,  highly  siliceous,  and  therefore  com- 
paratively light — in  other  words,  granitic  ;  beneath  this  was  a  less  oxi- 
dized, less  acid  layer,  and  so  on  progressively,  the  deeper  layers  becom- 
ing heavier  and  heavier,  and  more  and  more  basic.  The  first  eruptions 
were  from  the  outer  layer,  and  therefore  granitic.  Afterward,  as  the 
crust  grew  thicker  and  thicker,  the  eruptions  were  from  deeper  and 
deeper  layers,  and  therefore  denser  and  denser,  and  more  and  more 
basic. 

But,  in  answer  to  these  views,  it  may  be  said  that,  as  to  age,  there 
can  be  no  doubt  that  granite,  though  most  commonly  associated  with 
the  older  rocks,  is  found  in  strata  of  all  ages  up  to  the  middle  Tertiary, 
and  fissure  eruptions  have  occurred  in  all  ages  up  to  the  latest  Tertiary. 
The  granite  of  Mont  Blanc  was  pushed  up  at  the  end  of  the  Eocene 
(Lyell),  and  the  great  fissure-eruptions  of  the  Northwest  took  place 
at  the  end  of  the  Miocene  and  during  the  Pliocene.*  Also,  as  to  com- 
position, trachyte  and  liparite  have  much  the  same  chemical  composi- 
tion as  granite,  except  that  more  of  the  silica  is  in  combination  and  less 
of  it  free  in  the  former  than  in  the  latter.  Some  early  diorites  and 
gabbros  have  much  the  same  chemical  (if  not  mineral ogical)  composi- 
tion as  basalt. 

Again,  others,  with  much  reason,  think  that  all  the  differences  be- 
tween the  three  groups  in  mineralogical  character  and  crystalline 
structure  are  due  wholly  to  the  different  depths  at  which  and  the  slow- 
ness with  which  solidification  took  place.  They  think,  therefore,  that 
if  trachyte  (Fig.  180,  c)  could  be  traced  downward  deep  enough  it  would 
pass  into  porphyry  (#),  and  finally  into  granite  (g),  and  similarly  basalt 
would  pass  into  dolerite  and  diorite,  and  finally  into  olivin-diabase.f  On 
this  view,  what  we  can  not  do,  has  been  done  for  us  by  erosion ;  and 
granite  is  most  commonly  associated  with  older  rocks  only  because 
these  have  been  most  eroded,  and  therefore  their  deeper  parts,  or  even 
the  fountain-reservoirs  from  which  eruptions  have  come,  have  been 
exposed.  Similarly,  a  less  extreme  erosion  of  the  mesozoic  rocks  has 
exposed  the  porphyritic  and  dioritic  dikes  through  which  eruptions 
came  up ;  while,  of  the  modern  lavas,  only  the  upper  or  overflowed 
parts  are  exposed.  This  view  explains  completely  all  the  phenomena 
of  igneous  rocks,  and  the  gradations  between  them,  in  chemical  and 

*  American  Journal  of  Science,  vol.  vii,  p.  167,  1874. 

f  This  gradual  change  has  very  recently  been  distinctly  observed  in  Southeastern 
Europe  by  Judd  (Geological  Magazine,  1876,  vol.  xxxii,  p.  292),  and  also  in  Colorado  by 
Peale  (Hayden's  Report  for  1873,  p.  261),  and  also  by  Hague  and  Iddings  in  Nevada 
(United  States  Geological  Survey  Bulletin,  No.  17,  1885). 


218  UN  STRATIFIED   OR  IGNEOUS   ROCKS. 

mineralogical  composition  and  in  crystalline  structure,  and  is  therefore 
very  probably  true.  We  have  substantially  assumed  it  in  the  preceding 
descriptions. 

The  confusion  in  the  classification  and  nomenclature  of  igneous 
rocks  is  still  further  increased  by  the  undoubted  fact  that  many  of  the 
kinds  of  rocks  mentioned  above  as  igneous  are  found  also  among  met- 
amorphic  rocks  which  have  never  been  erupted  at  all.  This  subject  is 
further  treated  under  the  head  of  Metamorphism  (p.  223  et  seq.). 

3.  RiclitJioferi's  Classification  of  Tertiary  Eruptives. 

By  far  the  most  successful  attempt  to  classify  by  age,  or  to  corre- 
late the  kinds  of  igneous  rocks  with  their  ages,  is  found  in  Richt- 
hofen's  classification  of  Tertiary  eruptives.  According  to  Richthofen, 
there  is  a  regular  and  invariable  order  of  succession  among  the  erupt- 
ive rocks  of  Tertiary  times ;  the  order  being — 1.  Propylite.*  2.  Ande- 
site.  3.  Trachyte.  4.  Rhyolite.  5.  Basalt.  This  order,  however,  ap- 
plies only  io  primary  or  fissure  eruptions  ;  for,  since  primary  erupted 
masses  may  become  the  seats  of  subsequent  secondary  or  crater  erup- 
tions, it  is  evident  that  secondary  eruptions  of  a  lower  group  may  be 
synchronous  with  primary  eruptions  of  a  higher  group,  f 

These  views  of  Richthofen's  have  attracted  wide  attention,  but  have 
not  been  generally  confirmed.  All  that  is  as  yet  universally  accepted 
in  regard  to  the  order  of  Tertiary  eruptives  is  that  the  trachytes  (in- 
cluding in  this  term  with  the  trachytes  proper  also  the  andesites  and 
the  rhyolites)  precede  the  basalts.  The  reason  of  this  may  possibly  be 
found  in  the  fact  that  acidic  rocks,  although  more  infusible  than  the 
basics  to  dry  heat,  yet  yield  very  easily  to  hydrothermal  fusion  by  the 
formation  of  hydrous  silicates.  Now,  it  is  in  this  condition  of  imper- 
fect hydrothermal  fusion  that  the  trachytes  and  rhyolites  were  erupted, 
while  the  basalts  have  been  in  a  state  of  complete  igneous  fusion.  If 
we  suppose  strata  of  different  kinds  to  be  subjected  to  steadily  increas- 
ing heat  in  the  presence  of  a  small  percentage  of  water,  it  is  easily  con- 
ceivable that  the  acidic  rocks  would  first  yield  by  hydrothermal  fusion, 
and  only  afterward  the  basic  rocks  by  true  igneous  fusion. 

Judd,  in  his  recent  work  on  Volcanoes,  admits  that  an  intermediate 
type  like  andesite  (propylite  is  usually  regarded  as  a  variety)  is  first 
erupted,  then  an  acid  type  like  trachyte  and  rhyolite,  and  last  basalt. 
He  accounts  for  this  by  supposing  a  homogeneous  fused  mass  (such  as 
would  be  formed  by  fusion  of  many  different  kinds  of  strata),  to  be 
first  erupted  as  soon  as  formed.  This  would  make  an  intermediate 

*  Propylite  is  regarded  by  many  as  an  altered  andesite. 

f  Richthofen's  Natural  History  of  Volcanic  Rocks,  Memoirs  of  California  Academy  of 
Science,  vol.  i,  Part  II. 


METAMORPIIIC   ROCKS.  219 

type.  The  remainder  of  the  fused  mass  after  long  standing  would 
separate  into  a  lighter  acid  portion  above  and  a  heavier  basic  portion 
below.  These  would,  therefore,  be  successively  erupted  as  rhyolite  and 
basalt. 


CHAPTER  IV. 
METAMORPHIC  ROCKS. 

THERE  is  a  third  class  of  rocks,  intermediate  in  character  between 
the  ordinary  sedimentary  and  the  igneous  rocks,  and  therefore  put  off 
until  these  had  been  described.  The  rocks  of  this  class  are  stratified, 
like  the  sedimentary,  but  crystalline,  though  never  glassy,  and  usually 
non-fossiliferous,  like  the  igneous-  rocks.  They  graduate  insensibly  on 
the  one  hand  into  the  true  unchanged  sediment,  and  on  the  other  into 
true  igneous  rocks. 

Origin. — Their  origin  is  evidently  sedimentary,  like  other  stratified 
rocks,  but  they  have  been  subsequently  subjected  to  heat  and  other 
agents  which  have  changed  their  structure,  sometimes  entirely  destroy- 
ing their  fossils  and  even  their  lamination  structure,  and  inducing  in- 
stead a  crystalline  structure.  The  evidence  of  their  sedimentary  origin 
is  found  in  their  gradation  into  unchanged  fossiliferous  strata ;  the 
evidence  of  their  subsequent  change  by  heat,  in  their  gradation  into 
true  igneous  rocks.  For  this  reason  they  are  called  metamorphic 
rocks. 

Position. — All  the  lowest  and  oldest  rocks  are  metamorphic.  The 
converse,  however,  viz.,  that  metamorphic  rocks  are  always  among  the 
oldest,  is  by  no  means  true.  Metamorphism  is  not,  therefore,  a  test  of 
age.  Metamorphic  rocks  are  found  of  all  ages  up  to  the  Tertiary.  The 
Coast  Range  of  California  is  much  of  it  metamorphic,  although  the 
strata  belong  to  the  Tertiary  and  Cretaceous  periods.  Metamorphism 
seems  to  be  universal  in  the  Laurentian,  is  general  in  the  Palaeozoic, 
frequent  in  the  Mesozoic,  exceptional  in  the  Tertiary,  and  entirely 
wanting  in  recent  sediments.  It  is  therefore  less  and  less  common  as 
we  pass  up  the  series  of  rocks.  The  date  of  metamorphism  is  also 
different  from  that  of  the  origin  of  the  strata.  Metamorphism  has 
taken  place  in  all  geological  periods,  and  is  doubtless  now  progressing 
in  deeply-buried  strata. 

Metamorphism  is  also  generally  associated  with  foldings,  tiltings,  in- 
tersecting dikes,  and  other  evidences  of  igneous  agency,  and  is  there- 
fore chiefly  found  in  mountainous  regions.  It  is  also  usually  found 
only  in  very  thick  strata. 

Extent  on  the  Earth-Surface.— These  rocks  exist,  outcropping  on 


220 


METAMORPHIC   KOCKS. 


only  be  observed  in  large  masses. 


the  surface,  over  wide  regions.  Nearly  the  whole  of  Canada  and  Labra- 
dor, a  large  strip  on  the  eastern  slope  of  the  Appalachians,  and  a  large 
portion  of  the  mountainous  regions  of  the  western  border  of  this  con- 
tinent, are  composed  of  them.  Beneath  the  surface  they  probably  un- 
derlie all  other  stratified  rocks,  and  are  therefore  the  most  widely  dif- 
fused of  all  rocks.  Their  thickness  is  also  often  immense.  The  Lau- 
rentian  series  of  Canada  is  probably  50,000  feet  thick,  and  metamorphic 
throughout. 

Principal  Kinds. — The  principal  kinds  of  metamorphic  rocks  are : 
Gneiss,  mica-schist,  chlorite- schist,  talcose-schist,  hornblende-schist, 
clay-slate,  quartzite,  marble,  and  serpentine. 

Gneiss,  the  most  universal  and  characteristic  of  these  rocks,  has  the 
general  appearance  and  mineral  composition  of  granite,  except  that  it  is 
more  or  less  distinctly  stratified.  Often,  however,  the  stratification  can 

Gneiss  runs  by  insensible  gradations, 
on  the  one  hand,  into 
granite,  and  on  the  other, 
through  the  more  per- 
fectly stratified  schists, 
into  sandy  clays  or  clayey 
sands. 

The  schists  are  usu- 
ally grayish .  fissile  rocks, 
made  up  largely  of  scales 
of  mica,  or  chlorite,  or  talc.  Hornblende-schist  is  similarly  made  up  of 
scales  of  hornblende,  and  is  therefore  a  very  dark  rock.  The  fissile 
structure  of  schists  is  due  to  the  presence  of  these  scales,  and  is  there- 
fore wholly  different  from  that  of  slates.  It  is  called  foliation-struct- 
ure. 

Serpentine  is  a  compact,  greenish  magnesian  rock.  The  other  va- 
rieties need  no  description.  Hornblende-schists  run  by  insensible  gra- 
dations into  clay-slates  on  the  one  hand,  and  into  diorites  and  syenites 
on  the  other. 

All  these  kinds  may  be  regarded  as  changed  sands,  limestones,  and 
clays,  the  infinite  varieties  being  the  result  of  the  difference  in  the  original 
sediments  and  the  degrees  of  metamorphism.  Sands  and  limestones  are 
often  found  very  pure ;  such  when  metamorphosed  produce  quartzite 
and  marble.  Clays,  on  the  contrary,  are  almost  always  impure,  con- 
taining sand,  lime,  iron,  magnesia,  etc.  Such  impure  clays,  if  sand  is 
in  excess,  produce  by  metamorphosis  gneiss,  mica-schist,  and  the  like ; 
but  if  lime  and  iron  are  in  considerable  quantities  they  produce  horn- 
blende-schist or  clay-slate ;  if  magnesia,  talcose-schist.  The  origin  of 
serpentine  is  not  well  understood  ;  but  it  is  evidently  in  many  cases  a 
changed  magnesian  clay.  All  gradations  between  such  clays  and  ser- 


FIG.  191.— Gneiss. 


THEORY    OF   METAMORPHISM.  221 

pentine  may  be  found  in  the  Tertiary  and  Cretaceous  strata  of  the 
Coast  Eange  of  California.  But  it  is  also,  often,  a  changed,  igneous 
rock  containing  much  olivin  (peridotite). 

Theory  of  Metamorphism. 

There  are  few  subjects  more  obscure  than  the  cause  of  metamor- 
phism,  and  the  conditions  under  which  it  occurs.  Some  important 
light  has  been  thrown  on  it,  however,  recently.  For  the  sake  of  clear- 
ness, it  will  be  better  to  divide  metamorphism  into  two  kinds,  some- 
what different  in  their  causes,  viz.,  local  and  general. 

Local  MetamorpMsm  is  that  produced  by  direct  contact  with  evi- 
dent sources  of  intense  heat,  as  when  dikes  break  through  stratified 
rocks.  As  already  seen  (p.  210),  under  these  circumstances,  impure 
sandstones  are  changed  into  schists,  or  into  gneiss ;  clays  into  slates,  or 
into  porcelain  jasper;  limestones,  into  marbles;  and  bituminous  coal, 
into  coke,  or  into  anthracite.  In  these  cases  it  is  evident  that  the 
cause  of  the  change  is  the  intense  heat  of  the  incandescent,  fused  con- 
tents of  the  dike  at  the  moment  of  filling.  In  such  cases  of  local  meta- 
morphism,  the  effects  usually  extend  but  a  few  yards  from  the  wall  of 
the  dike. 

General  MetamorpMsm. — But  in  many  cases  we  can  not  trace  the 
change  to  any  evident  source  of  intense  heat.  Kocks  thousands  of  feet 
in  thickness,  and  covering  hundreds  of  thousands  of  square  miles,  are 
universally  changed.  The  principal  agents  of  this  general  metamor- 
phism seem  to  be  heat,  water,  alkali,  pressure. 

That  heat  is  a  necessary  agent  is  sufficiently  evident  from  the  gen- 
eral similarity  of  the  results  to  local  metamorphism.  But  that  the  heat 
was  not  intense,  and  therefore  not  sufficient  of  itself  to  produce  the 
effects,  is  also  quite  certain.  For  (a)  metamorphic  rocks  are  often 
found  interstratified  with  unchanged  rocks.*  Intense  heat  would  have 
affected  them  all  alike,  or  nearly  alike,  (b.)  Many  minerals  are  found 
in  metamorphic  rocks  which  will  not  stand  intense  heat.  As  an  example, 
carbon  has  been  found  in  contact  with  magnetic  iron-ore,  although  it 
is  known  that  this  contact  can  not  exist,  even  at  the  temperature  of  red- 
heat,  without  reduction  of  the  iron-ore,  (c.)  The  effect  of  simple  dry 
heat,  as  shown  in  cases  of  local  metamorphism,  does  not  extend  many 
yards,  (d.)  Water-cavities  are  found  abundantly  in  metamorphic  rocks. 
This  will  be  more  fully  explained  farther  on. 

Water.— Heat  combined  with  water  seems  to  be  the  true  agent. 
Recent  experiments  of  Daubree,  Senarmont,  and  others,  prove  that 
water  at  400°  C.  (=  752°  Fahr.)  reduces  to  a  pasty  condition  nearly  all 
ordinary  rocks ;  moreover,  that  at  this  temperature  crystals  of  quartz, 

*  American  Journal  of  Science,  vol.  xxi,  p.  327,  1881. 


222 


METAMORPHIC  ROCKS. 


feldspar,  mica,  augite,  etc.,  are  formed.  In  fact,  as  Guthrie  has  shown 
(Geological  Magazine,  vol.  vi,  p.  244,  1889),  there  are  all  gradations 
between  solution  and  true  igneous  fusion  through  various  grades  of 
hydrothermal  fusion.  Such  a  pasty  or  aqueo-fused  mass  slowly  cooled 
would  form  a  crystalline  rock  containing  crystals  of  quartz,  feldspar, 
mica,  etc. ;  in  other  words,  would  be  metamorphic.  The  quantity  of 
water  necessary  for  these  effects  is  shown  by  experiment  to  be  very 
small — only  five  to  ten  per  cent.  In  other  words,  the  included  ivater 
of  sediments  is  amply  sufficient. 

Alkali. — Alkaline  carbonates,  or  alkaline  silicates,  so  common  in 
natural  waters,  greatly  promote  the  process,  causing  the  aqueo-igneous 
pastiness  or  aqueo-igneous  fusion  to  take  place  at  a  much  lower  tem- 
perature. 

Pressure. — Pressure  is  a  necessary  condition  of  the  existence  of 
high  temperature  in  the  presence  of  water,  and  is  thus  an  indirect 
agent  of  metamorphism,  but  it  is  also  a  direct  agent,  since  it  increases 
chemical  action  of  many  kinds,  and  therefore  solubility. 

It  is  evident,  therefore,  that  while  metamorphism  by  dry  heat  would 
require  a  temperature  of  2,000°  to  3,000°  Fahr.,  in  the  presence  of  water 
the  same  result  is  produced  at  572°  to  752°  Fahr.  (300°  or  400°  C.) ;  or 
in  the  presence  of  alkali,  even  in  small  amount,  probably  at  300°  or 
400°  Fahr. 

Application. — All  these  agents  are  found  associated  in  deeply-buried 
sediments.  Series  of  outcropping  strata  are  often  found  20,000  or  even 
40,000  feet  .thick.  The  lower  strata  of  such  a  series  by  the  regular 
increase  of  interior  heat  alone,  must  have  been,  before  uptilting,  at  a 
temperature  of  between  700°  and  800°  Fahr.,  a  temperature  sufficient, 
with  their  included  water,  to  produce  complete  aqueo-igneous  pastiness, 
and  therefore,  by  cooling  and  crystallization,  complete  metamorphism. 
Suppose,  then,  «,  sb,  Fig.  192,  represent  the  contour  of  land  and 
sea-bottom  at  the  beginning  of  any  period,  and  the  dotted  lines  the 

isogeotherm  of 
400°  and  800°. 
If,  now,  sedi- 
ments 40,000  to 
50,000  feet  thick 
be  deposited  so 
that  the  sea-bot- 
tom is  raised  to 
s'b')  then  the  iso- 
therm of  800° 

will  rise  to  the  position  of  the  broken  lines  and  invade  the  lower  por- 
tions of  the  sediments  with  their  included  water.  Such  sediments 
would  be  completely  changed  in  their  lower  portions,  and  to  a  less  ex- 


FIG.  192.— sb,  original  sea- bottom;  $'b',  sea-bottom  after  sediments,  sd, 
have  accumulated:  .  .  .  .,  isogeotherms  of  800'  and  400°  :  — .  — . — , 
same  after  accumulation  of  sediments. 


ORIGIN   OF   GRANITE.  223 

tent  higher  up.  It  is  probable  that  even  300°  to  400°  Fahr.  is  sufficient 
to  produce  a  considerable  degree  of  change ;  or  even  200°,  if  alkali  be 
present. 

Crushing:. — Although  simple  gravitative  pressure  is  only  a  condi- 
tion, and  not  a  cause,  of  heat,  horizontal  pressure  with  crushing  of  the 
crust,  by  the  conversion  of  mechanical  energy  into  heat,  becomes,  as 
Mallet  has  shown,*  an  active  source  of  this  agent.  Now,  in  all  cases 
of  metamorphism  we  find  ample  evidences  of  such  horizontal  crushing 
in  the  associated  foldings  and  cleavage  of  the  strata. 

Mechanical  Metamorphism. — Very  recently  it  has  been  shown  that 
lateral  .pressure  with  crushing  and  shearing,  and  sometimes  even  a  kind 
of  flowing  of  the  crushed  rock,  will  produce  a  schistose  structure  not 
only  in  stratified  but  even  in  igneous  rocks.  This  has  been  called 
mechanical  or  dynamical  metamorphism.  Thus  the  difficulty  of  deter- 
mining the  origin  of  metamorphic  rocks  becomes  still  greater. 

Again,  percolating  water  containing  silica,  even  at  ordinary  tem- 
perature and  pressure,  but  especially  at  high  temperature  under  heavy 
pressure,  may  often  fill  up  by  crystallization  the  interstices  of  a  sand- 
rock  so  as  to  make  a  perfect  quartzite.  f 

Explanation  of  Associated  Phenomena.— This  theory  readily  ex- 
plains— 1.  Why  metamorphism  is  always  associated  with  great  thick- 
ness of  strata;  2.  Why  the  oldest  rocks  are  most  commonly  meta- 
morphic, since  these  have  usually  had  the  newer  rocks  piled  upon 
them,  and  have  been  subsequently  exposed  by  erosion.  The  newer 
rocks  are  sometimes  also  metamorphic,  but  in  these  cases  they  are  very 
thick.  3.  It  also  explains  the  interstratification  of  metamorphic  with 
unchanged  rocks ;  since  some  rocks  are  more  easily  affected  by  heated 
water  than  others,  and  the  composition  of  the  included  water  may  be 
also  different,  some  containing  alkali  and  some  not.  4.  It  also  explains 
its  association  with  foldings  of  strata  and  with  mountain-chains,  as  will 
be  more  fully  explained  hereafter. 

If  metamorphism  is  only  produced  in  deeply-buried  sediments,  then 
the  exposure  of  such  rocks  on  the  surface  can  only  result  f ron  exten- 
sive erosion. 

Origin  of  Granite. 

No  doubt  many  granites  are  the  consolidated  reservoirs  from  which 
eruptions  have  come ;  but  there  is  much  reason  to  believe  that  most 
granites  are  not  the  result  of  simple  dry  fusion,  as  is  usually  supposed ; 
but,  on  the  contrary,  only  the  last  term  of  metamorphism  of  highly- 
siliceous  sediments,  and  have  not  given  rise  to  eruptions  at  all.  Ac- 
cording to  this  view,  incipient  pastiness  by  heat  and  water  makes 

*  Philosophical  Transactions,  1873,  p.  147. 

f  Irving,  American  Journal,  vol.  xxv,  p.  402,  1883,  and  vol.  xxxi,  p.  225,  1886. 


224  METAMORPHIC   ROCKS. 

gneiss ;  complete  pastiness,  completely  destroying  stratification,  makes 
granite.  The  principal  arguments  for  this  view  may  be  briefly  stated 
as  follows :  * 

1.  In  many  localities  in  mountain-regions,  and  nowhere  better  than 
in  the  Sierra  of  California,  every  stage  of  gradation  may  be  observed 
between  clayey  sandstones  and  gneiss,  and  between  gneiss  and  granite. 
So  perfect  is  this  gradation,  that  it  is  impossible  to  draw  sharply  the 
distinction.     Even  geologists  who  believe  that  granite  is  the  primitive 
rock  have  been  compelled  to  admit  that  there  is  also  a  metamorphic 
granite,  scarcely  distinguishable  from  primitive  granite. 

2.  Not  only  gneiss,  but  even  granite,  is  sometimes,  interstratified 
with  undoubted  sedimentary  rocks,  f 

3.  Chemists  recognize  two  kinds  of  silica,  viz.,  an  amorphous  va- 
riety of  specific  gravity  2-2,  and  a  crystallized  variety,  specific  gravity 
2-6.     These  two  varieties  differ  from  each  other  not  only  in  density, 
but  also  in  chemical  properties,  the  former  being  much  more  easily 
attacked  by  alkalies  than  the  latter.     By  solidification  from  fusion  (dry 
way)  only  the  variety  of  specific  gravity  2-2  can  be  formed,  while  the 
variety  2'6  is  formed  only  by  slow  deposit  from  solution  (humid  way).J 
Now,  the  quartz  of  granite  is  always  of  the  variety  2 -6,  and  therefore 
must  have  been  formed  in  presence  of  water. 

4.  Crystals  of  quartz,  hornblende,  and  mica,  are  frequently  formed 
in  Nature  by  the  humid  process,  as,  for  example,  in  metamorphic  rocks ; 
and  have  also  been  artificially  formed  by  the  same  process  by  Daubree, 
Senarmont,  and  others,  as  already  stated  (p.  221) ;  but  they  have  never 
been  formed  artificially  by  the  dry  way. 

5.  In  nearly  all  rocks  and  minerals  microscopic  cavities  are  found 
indicating  the  conditions  under  which  crystallization  or  solidification 
took  place.     If  crystals  are  formed  by  sublimation,  they  contain  vacu- 
ous cavities.     If  they  are  formed  by  solidification  from  fusion  (dry  way), 
and  if  gases  or  vapors  are  present,  they  may  contain  vapor-blebs ;  but, 
if  they  crystallize  slowly  from  a  glassy  magma,  they  contain  spots  of 
glassy  matter,  or  glass  cavities  or  inclusions,  as  in  slags  and  lavas.     If 
they  are  formed  by  crystallization  from  solution,  then  they  have  flui d 
cavities,  or  liquid  inclusions,  as  they  are  now  usually  called.     Now,  not 
only  are  these  fluid  cavities  found  in  metamorphic  rocks,  but  also  in 
the  quartz  and  feldspar  of  granite.     "  A  thousand  millions  of  these 
microscopic  cavities  in  a  cubic  inch  is  not  at  all  unusual ;  and  the  in- 
closed water  often  constitutes  one  to  two  per  cent  of  the  volume  of  the 

*  Rose,  Philosophical  Magazine,  xix,  p.  32  ;  Delesse,  Archives  des  Sciences,  vol.  vii,  p. 
190;  Hunt,  American  Journal  of  Science  and  Arts,  new  series,  vol.  i,  pp.  82,  182. 

f  Dana,  American  Journal  of  Science,  vol.  xx,  p.  194,  1880. 

\  Recently  quartz,  specific  gravity  2'6,  has  been  formed  under  peculiar  conditions  by 
dry  fusion,  American  Journal  of  Science,  vol.  xvi,  p.  155,  1878. 


ORIGIN  OF  GRANITE.  225 

quartz."*  Besides  these  fluid  cavities,  however,  glass  cavities  are  also 
found  in  the  quartz  and  feldspar  of  granite.  These  facts  point  plainly 
to  the  agency  of  both  heat  and  water  in  the  formation  of  granite. 
Among  the  liquids  thus  inclosed  in  granite  and  other  metamorphic 
rocks  is  often  found  liquid  carbonic  acid.  This  fact  shows  the  great 
pressure  under  which  solidification  of  the  rock  took  place. 

Even  the  temperature  at  which  metamorphic  rocks  and  granite 
solidified  has  been  approximately  determined  by  Mr.  Sorby.  The  prin- 
ciple on  which  this  is  done  is  as  follows :  If  crystallization  from  solu- 
tion, or  solidification  in  the  presence  of  water,  take  place  at  ordinary 
temperatures,  then  the  fluid  cavities  will  be  full ;  but  if  at  high  tem- 
peratures, and  the  mass  subsequently  cools,  then  by  the  contraction  of 
the  contained  liquid  a  vacuous  space  will  be  formed  which  will  be 
larger,  in  proportion  to  the  amount  of  contraction,  and  therefore  to 
the  temperature  of  solidification.  Knowing,  therefore,  the  relative 
sizes  of  the  vacuole  and  the  contained  water,  and  the  coefficient  of  ex- 
pansion of  the  water  and  the  rock,  the  temperature  at  which  the  cavity 
would  fill  (which  is  the  temperature  of  solidification)  may  be  calculated. 
Sometimes  this  temperature  may  be  gotten  by  actual  experiment,  i.  e., 
by  heating  until  the  cavity  fills.  By  this  method  Mr.  Sorby  has  deter- 
mined the  temperature  of  solidification  of  certain  metamorphic  rocks 
of  Cornwall  as  392°  Fahr.,  and  of  some  granites  as  482°,  and  others 
only  212°. 

It  seems  almost  certain,  therefore,  that  many  granites  have  not  been 
formed  by  dry,  igneous  fusion.  Yet  that  this  rock  has  been  in  a  liquid 
or  pasty  condition  is  perfectly  certain  from  its  occurrence  in  tortuous 
veins.  Therefore  it  has  been  rendered  pasty  by  heat  in  the  presence 
of  water  under  great  pressures,  such  as  always  exist  in  deeply-buried 
strata.  The  weight  of  the  superincumbent  strata,  or  else  pressure  by 
folding  and  crushing  of  the  strata,  has  forced  it  into  cracks  and  great 
fissures. 

What  we  have  said  of  granite  applies  of  course  to  the  whole  gra- 
nitic group.  Granitic  rocks  are  often  only  the  last  term  of  the  metamor- 
phism  of  sediments ;  granite  being  produced  from  the  more  siliceous 
sediments,  and  diabase  and  gabbro  from  the  more  basic  impure  clays. 
But  'we  can  not  stop  with  this  group.  It  is  certain  that  many  if  not 
all  the  rocks  of  the  Trappean  group  also  may  be  made  by  metamor- 
phism  of  sediments.  Many  bedded  diorites,  dolerites,  and  felsites,  are 
undoubtedly  formed  in  this  way,  for  the  gradations  can  be  distinctly 
traced  into  slates.  Prof.  Dana  f  has  recently  recognized  this  as  so  cer- 
tain that  he  proposes  the  addition  of  the  prefix  meta  to  these  to  indi- 

*  Sorby,  Quarterly  Journal  of  the  Geological  Society,  vol.  xiv,  pp.  329,  453. 
f  American  Journal  of  Science  and  Arts,  vol.  xi,  p.  119,  February,  1876. 
15 


226  STRUCTURE  COMMON  TO  ALL  ROCKS. 

cate  their  origin.  Thus  he  recognizes  a  syenite  and  a  metasyenite,  a 
diorite  and  a  metadiorite,  dolerite  and  metadolerite,  felsite  and  meta- 
felsite,  etc.,  and  we  might  add  granite  and  metagranite. 

Many  geologists  push  these  views  so  as  to  include  also  even  the 
true  lavas.  Deeply-buried  sediments  under  gentle  heat  in  the  presence 
of  water  and  pressure  undergo  incipient  change  and  form  metamorphic 
rocks;  under  greater  heat  become  pasty  and  form  granite,  meta- 
syenites,  metadiorites,'  metafelsites,  etc.;  under  still  greater  heat,  in- 
creased probably,  as  Mallet  suggests,  by  mechanical  energy  in  crushed 
strata  being  converted  into  heat,  become  completely  fused,  and  ap  then 
outpoured  upon  the  surface  either  by  the  elastic  force  of  the  steam 
generated,  or  by  the  pressure  and  squeezing  produced  by  the  folding  of 
the  crust  of  the  earth,  so  common  in  mountainous  regions.  According 
to  this  view,  every  portion  of  the  earth's  crust  has  been  worked  over  and 
over  again,  passing  through  the  several  conditions  of  soil,  sediment, 
stratified  rock,  metamorphic  rock,  and  igneous  rock,  perhaps  many 
times  in  the  course  of  the  geological  history  of  the  earth,  and  we  look 
in  vain  for  the  primitive  rock  of  the  earth's  crust. 


CHAPTER  V. 
STRUCTURE  COMMON  TO  ALL  ROCKS. 

WE  have  thus  far  given  a  brief  description  of  the  three  classes  of 
rocks,  their  structure  and  mode  of  occurrence.  There  are  still,  how- 
ever, several  important  kinds  of  structure  which  are  common  to  all 
these  classes  of  rocks,  and  require  description.  These  are  joints,  fis- 
sures, and  veins.  Mountain- chains,  as  involving  all  kinds  of  rocks  and 
all  kinds  of  structure,  and  as  summing  up  in  their  discussion  all  the 
principles  of  structural  and  dynamical  geology,  must  be  taken  up  last. 

SECTION  1. — JOINTS  AND  FISSUKES. 
Joints. 

All  rocks,  whether  stratified  or  igneous,  are  divided,  by  cracks  or 
division-planes,  in  three  directions,  into  separable  irregularly  prismatic 
blocks  of  various  sizes  and  shapes.  These  cracks  are  called  joints.  In 
stratified  rocks  the  planes  between  the  bedding  constitute  one  of  these 
division-planes,  while  the  other  two  are  nearly  at  right  angles  to  this 
and  to  each  other,  and  are  true  joints.  In  igneous  rocks  all  the 
division-planes  are  of  the  nature  of  joints.  In  sandstone  these  blocks 
are  large  and  irregularly  prismatic ;  in  slate,  small,  confusedly  rhom- 


FISSURES,  OR  FRACTURES. 


227 


boidal ;  in  shale,  long,  parallel,  straight ;  in  limestone,  large,  regular, 
cubic ;  in  basalt,  regular,  jointed,-columnar ;  in  granite,  large,  irregularly 


FIG.  193.— Regular  Jointing  of  Limestone. 

cubic,  or  irregularly  columnar.  On  this  account  a  perpendicular  rocky 
cliff  usually  presents  the  appearance  of  huge,  irregular  masonry,  with- 
out cement. 

The  cause  of  joints 
is  probably  the  shrink- 
age of  the  rock  in  the 
act  of  consolidation  from 
sediments  (lithification), 
as  in  stratified  rocks,  or 
in  cooling  from  a  pre- 
vious condition  of  high 
temperature,  as  in  the 
igneous  and  metamor- 

phic  rocks.*  pIG.  194.— Granitic  Columns. 

Fissures,  or  Fractures. 

These  must  not  be  confounded  with  joints.  Joints  are  cracks  in 
the  individual  strata  or  beds;  fissures  are  fractures  in  the  earth's 
crust,  passing  through  many  strata,  and  even  sometimes  through  many 
formations.  The  former  are  produced  by  shrinkage  and  perhaps  other 
causes  ;  the  latter  by  movements  of  the  earth's  crust.  Fissures,  there- 
fore, are  often  fifty  or  more  miles  in  length,  thirty  to  fifty  feet  in  width, 
and  pass  downward  to  unknown  but  certainly  very  great  depths.  They 
often  break  through  the  crust  into  the  sub-crust  liquid. 

*  Daubree  thinks  that  joints  are  due  to  crust-movements,  especially  by  torsion  ;  and 
therefore  that  there  are  all  gradations  between  joints  and  great  fissures  (Geologic  Syn- 
thetique). 


228 


STRUCTURE   COMMON  TO  ALL  ROCKS. 


Cause. — The  cause  of  great  fissures  is  evidently  always  movements, 
either  by  foldings  or  by  liftings  of  the  earth's  crust.  In  either  case 
there  would  be  formed  a  parallel  system  of  fissures  in  the  direction  of 
the  folds,  and  therefore  at  right  angles  to  the  direction  of  the  folding 
or  lifting  force.  Fissures  are.  usually  thus  found  in  systems  parallel 
among  themselves,  and  to  the  axes  of  mountain-chains.  Through  such 
fissures  igneous  rooks  in  a  fused  condition  are  often  forced,  forming 
dikes  and  overflowing  sheets.  Besides  the  principal  fissures  just  ex- 
plained, Hopkins  has  shown  that,  in  the  case  of  the  formation  of  mount- 
ains, there  would  be  formed  also  other  smaller  fissures  at  right  angles 
to  these. 

Nearly  always  the  walls  on  the  two  sides  of  a  fissure  do  not  corre- 
spond with  each  other,  but  one  side  has  been  pushed  up  higher  or 
dropped  down  lower  than  the  other.  Such  a  displacement  is  called  a 
fault,  a  slip,  or  dislocation.  This  may  occur  in  fissures  in  any  kind  of 
rock,  but  is  most  marked  and  most  easily  distinguished  in  stratified 
rocks.  When  the  strata  are  sufficiently  flexible  to  admit  it,  they  are 
bent  instead  of  broken,  and  a  monoclinal  fold  is  formed  instead  of  a 
fault  (Fig.  195).  When  the  fissure  is  filled  at  the  moment  of  its  forma- 


FIG.  195.— Section  of  Nutria-Fold,  New  Mexico  (after  Gilbert). 

tion  with  fused  matter  from  beneath,  it  is  called  a  dike.  When  it  is  not 
filled  at  the  moment  of  its  formation  with  igneous  injection,  but  slowly 
afterward  with  other  matter,  and  by  a  different  process,  it  is  called  a 
vein.  Dikes  we  have  already  discussed  (p.  209) ;  veins  we  will  discuss 
later ;  we  are  concerned  here  only  with  faults. 

Faults. — In  faults  the  extent  of  vertical  displacement  varies  from  a 
few  inches  to  hundreds  or  even  thousands  of  feet.  In  the  Appalachian 
chain  there  occur  faults  in  which  the  vertical  dislocation  is  5,000  to 


FIG.  196.— Fault  in  Southwest  Virginia:  a,  Silurian;  d,  carboniferous  (after  Lesley). 


FISSURES,   OR  FRACTURES. 


229 


30,000  feet.  In  Southwest  Virginia,  accord- 
ing to  Rogers,  there  is  a  line  of  fracture  ex- 
tending parallel  to  the  Appalachian  chain 
for  eighty  miles,  in  which  there  is  a  vertical 
slip  of  8,000  feet,*  the  Lower  Silurian  being 
brought  up  on  one  side  until  it  comes  in  con- 
junction with  the  Lower  Carboniferous  on 
the  other  (Fig.  19G).  In  Western  Pennsyl- 
vania, according  to  Leslie,  there  is  another 
fault  extending  for  twenty  miles,  in  which 
the  lowermost  of  the  Lower  Silurian  is 
brought  up  on  a  level  with  the  uppermost  of 
the  Upper  Silurian,  the  whole  Silurian  strata 
being  at  this  place  20,000  feet  thick,  so  that 
one  may  stand  astride  of  the  fissure  with  one 
foot  on  the  Trenton  limestone  (Lower  Silu- 
rian), and  the  other  on  the  Hamilton  shales 
(Devonian).f  On  the  north  side  of  the 
Uintah  Mountains,  there  is  a  slip,  according 
to  Powell,  of  nearly  20,000  feet.  J  The  Sevier 
Valley  fault,  Utah,  may  be  traced  partly  as  a 
slip,  partly  as  a  monoclinal  fold,  for  225  miles 
(Gilbert).  On  the  west  side  of  the  Wahsatch 
range  there  is  a  fault  of  40,000  feet  (King),* 
and  on  the  east  side  of  the  Sierra  one  of  at 
least  15,000  feet.  || 

But  nowhere  on  this  continent,  or  per- 
haps in  the  world,  are  fissures  and  faults  de- 
veloped on  so  grand  a  scale  as  in  the  high 
Plateau  region,  i.  e.,  the  region  bounded  by 
the  Wahsatch,  the  Uintah,  and  the  Colorado 
Mountains.  The  whole  of  this  elevated  re- 
gion is  traversed  by  a  system  of  north  and 
south  fissures,  extending  for  hundreds  of 
miles,  by  which  the  almost  horizontal  strata 
are  broken  into  huge  oblong  prismatic  blocks 
many  miles  wide.  The  slipping  of  these 
blocks,  some  to  a  higher  and  some  to  a  lower 
level,  with  a  difference  of  1,000  to  5,000  feet, 

*  Dana's  Manual,  p.  399.         f  Manual  of  Coal,  p.  147. 
J  Exploration  of  Colorado  River,  p.  156. 

*  Survey  of  the  Fortieth  Parallel,  vol.  i,  pp.  728-746. 
||  Le  Conte,  American  Journal  of  Science,  vol.  xvi,  p 

101,  1878. 


i 


ft  41, 


n 

:~     1  '/ 


230 


STRUCTURE  COMMON  TO  ALL  ROCKS. 


or  even  in  some  cases  12,000  feet,  has  given  rise  to  the  remarkable 
series  of  north  and  south  cliffs,  which,  together  with  the  equally  re- 
markable east  and  west  cliffs,  due  to  erosion,  to  be  described  hereafter 
(p.  270),  form  so  striking  a  feature  of  the  scenery  of  this  region.  The 
accompanying  section  and  perspective  view  (Fig.  197),  taken  from 
Powell,  shows  several  of  these  occurring  in  a  distance  of  90  miles. 

These  fissures  were  formed  by  the  elevation  of  the  Plateau  region, 
and  are  parallel  to  the  axis  of  elevation  ;  on  each  side  of  which  they  are 
arranged  with  wonderful  regularity.  They  were  formed  in  very  recent 
geological  times,  probably  late  Pliocene  and  Quaternary,*  and  possibly 
reaching  even  into  the  present  epoch,  and  are  therefore  little  affected 
by  erosion.  Add  to  this  the  nakedness  of  the  rocks  and  the  horizon- 

tality  of  the  strata,  and  it 
is  easy  to  see  what  an  ad- 
mirable  field  is  here  af- 

forded  for  the  study  of 

*    i^ 
faults. 

If  such  slips  were 
suddenly  produced  by 
violent  convulsion,  then, 
at  the  time  of  formation, 
there  must  have  been  a 
steep  (Fig.  198)  or  some- 
times even  an  overhanging  escarpment  (Fig.  196),  equal  to  the  dis- 
placement. In  some  cases  there  is  such  an  escarpment  or  line  of  steep 
mountain-slope  corresponding  to  the  line  of  slip.  In  the  Colorado 
Plateau  region  the  north 
and  south  cliffs  are  pro- 
duced by  faults  (Powell). 
The  Zandia  Mountains, 
New  Mexico,  are  pro- 
duced  by  a  drop  of  11,- 
000  feet  on  the  western 
side,  leaving  an  escarp- 
ment still  7,000  feet  high 
(Gilbert).  The  precipi- 
tous eastern  slope  of  the 
Sierra  and  western  slope 


FIG.  198. 


'••*... 


of  the  Wahsatch  are  the 


FIG.  199.— Strata  repeated  by  Faults. 


result  of  faults.  In  the  Basin  Kange  region  also  many  of  the  ridges 
are  formed  by  faults.  But  in  many  cases  there  is  no  such  escarpment, 
the  two  sides  of  the  fault  having  been  cut  down  to  one  level  by  sub- 


*  Putton,  Geology  of  the  High  Plateaus,  p.  35. 


FISSURES,   OR  FRACTURES. 


231 


sequent  erosion,  so  that  the  unpractised  eye  detects  nothing  unusual 
along  the  line  of  fracture  and  slip.  In  Fig.  198  the  strong  line  a  a 
shows  the  present  surface,  while  the  dotted  line  1)1)  1}  shows  the  surface 
after  the  displacement  as  it  would  be  if  unaffected  by  erosion.  In 
many  cases,  however,  it  seems  more  probable  that  there  never  existed 
any  such  escarpment  as  represented  in  Fig.  198,  but  that  the  displace- 


FIG.  200.— Section  through  Portion  of  Plateau  "Region  of  Utah,  showing  a  Succession  of  Faults 

(after  Hovvell). 

ment  was  produced  by  a  sloiv,  creeping  motion,  or  else  by  a  succession 
of  smaller  sudden  slips  probably  accompanied  with  earthquakes  (p. 
113),  and  thus  that  the  slipping  and  the  denudation  have  gone  on  to- 
gether par  i  passu.  In  Fig.  227,  on  page  255,  the  upper  part  shows  the 
great  Uintah  fault 
restored,  while  the 
lower  part  shows  the 
actual  condition  of 
things  produced  by 


erosion. 

When  faults   OC-  Flo>  201--Fault  with  Change  of  Dip  :  d,  dike. 

cur  in  inclined  outcropping  strata,  the  same  series  of  strata  may  be  re- 
peated several  times,  as  in  Fig.  199.  In  such  a  case,  the  observer  walk- 
ing over  the  surface  of  the  country  from  A  to  B  might  suppose  here  a 

series  of  nine  strata,  whereas  there  are 
but  three  strata,  #,  b,  c,  three  times  re- 
peated. Fig.  200  is  a  natural  section 
showing  this.  Sometimes  the  dip  of 
the  strata  on  the  two  sides  of  a  fault 
are  not  parallel,  the  change  of  inclina- 
tion being  effected  at  the  time  of  the 
displacement,  as  shown  in  Fig.  201. 
Upon  the  eroded  surface  of  such  dis- 
located strata,  by  subsequent  subsi- 
dence, other  strata  may  be  unconformably  deposited  (Fig.  202). 

Law  of  Slip, — In  faults  the  plane  of  fracture  is  sometimes  vertical, 
but  much  more  generally  it  is  more  or  less  inclined.  In  such  cases,  in 
by  far  the  larger  number  of  great  faults,  the  strata  on  the  upper  side 
(hanging'  wall)  of  the  fracture  have  dropped  down,  while  the  strata  on 
the  lower  side  (foot-wall)  have  gone  up,  as  in.  Figs.  203  and  204  and 
nearly  all  the  previous  figures.  These  are  called  normal  faults.  In 
some  cases  of  strongly-folded  strata,  however,  the  hanging  wall  seems  to 
have  been  pushed  and  made  to  slide  upward  over  the  foot- wall  as  if  by 


FIG.  20^.— Unconformity  on  Faulted  Strata. 


232 


STRUCTURE   COMMON   TO  ALL  ROCKS. 


powerful  horizontal  squeezing.     This  is  the  case  with  the  great  slip  in 
Southwestern  Virginia,  represented  in  Fig.  196.     These  are  called  re- 


FIG.  203.— Section  across  Yarrow  Colliery,  showing  the  Law  of  Faults  (after  De  la  Beche). 

verse  faults.  In  several  hundred  cases  of  great  fissures,  examined  Ly 
Phillips,  in  England,  nearly  all  followed  the  law  of  normal  faults.*  Fig. 
203  is  a  section  across  Yarrow  Colliery,  in  which  all  the  slips  follow 
this  law.  Of  the  numerous  slips  figured  by  Powell,  Gilbert,  and  Howell, 
as  occurring  in  the  Plateau  and  Basin  Range  region,  nearly  all  follow 
this  law.  Fig.  204  is  a  section  illustrating  this  fact. 


East   *— 

FIG.  204.— Section  of  Pahranagat  Range,  Nevada,  showing  the  Law  of  Faults  (after  Gilbert). 

Explanation  of  the  Direction  of  Slipping. — Reverse  faults  are  nearly 
always  found  in  strongly-folded  strata  such  as  characterize  the  struct- 
ure of  most  moun- 
tain ranges,  and  are 
evidently  formed 
by  powerful  lateral 
pressure.  The 
manner  in  which 
folds  are  pushed 
over  until  they  be- 
come reverse  faults 
is  shown  in  the  ac- 
companying figures 
(Fig.  205,  A,B,  and 
C).  In  extreme 
cases  the  fault- 
plane  becomes  near- 
ly horizontal,  C. 
These  are  called 

Q  FIG.  205.— Diagrams  showing  how  Reverse  Faults  are  formed  (after  De 

S.  Margerie  and  Heim). 


*  Phillips's  Geology,  p.  35. 


FISSURES,   OR  FRACTURES. 


233 


The  explanation  of  normal  faults  is  not  so  obvious.  In  the  case 
of  great  faults  of  this  kind  the  explanation  is  probably  as  follows : 
Suppose  a  portion  of  crust  lifted  by  intumescence  of  sub-crust  layer, 
produced  either  by  access  of  water  from  above  or  by  hydrostatic  press- 
ure transferred  from  a  subsiding  area  in  some  other  perhaps  distant 
place.  The  crust  would  be  broken  by  more  or  less  parallel  fissures 
into  great  oblong  blocks  many  miles  in  extent.  Since  the  fissures 
are  usually  more  or  less  inclined,  these  crust-blocks  would  be  either 
rhomboidal  or  wedge-shaped  (Fig.  206,  A).  As  the  crust  rose  into 
an  arch  these  blocks  would  separate  (Fig.  206,  B).  As  soon  as  the 

~T~7t     /  i    /c\  d    /e  \    f    \     y    \ 


\7 


\       \ 


FIG.  206.— Diagrams  showing  how  Normal  Faults  are  probably  formed. 

tension  is  relieved  by  escape  of  elastic  vapors  or  lava  or  both,  the  blocks 
would  readjust  themselves  by  gravity  into  new  positions.  In  doing 
so  the  rhomboidal  blocks  abfg  would  tilt  over  on  the  overhanging 
side  and  heave  up  on  the  obtuse-angle  side,  producing  in  every  case 
normal  faults,  and  the  wedge-shaped  blocks  c  d  e  would  sink  bodily 
lower  or  float  bodily  higher  according  as  the  base  of  the  wedge  was 
upward  or  downward,  producing  again  in  every  case  normal  faults,  as 
shown  in  Fig.  206,  C.  The  result  of  such  readjustment  of  crust-blocks 
is  admirably  shown  on  a  large  scale  in  the  structure  of  the  Basin  re- 
gion, and  especially  in  Southeastern  Oregon  (Fig.  207).  The  fractur- 


FIG.  207.— Sketch  section  through  Warner  and  Abert  Lakes,  S.  E.  Oregon  (after  Russell).     W.  L., 
Warner  Lake ;  A.  L.,  Abert  Lake  ;  Cli.  V.,  Chemaukan  Valley. 

ing  and  tilting  here  have  been  so  recent  (beginning  of  Quaternary) 
that  erosion  has  had  little  effect  in  modifying  the  orographic  forms. 
It  is  seen  that  the  upheaved  side  of  every  crust-block  forms  a  mount- 
ain ridge,  while  the  dropped  side  forms  a  valley  on  which  drainage 
waters  accumulate  to  form  a  lake. 


234:  STRUCTURE   COMMON   TO  ALL  ROCKS. 


Thus  where  fissures  are  formed  by  lateral  p  f^ure  or  crushing,  re- 
verse faults  are  formed  ;  but  where  they  are  formed  by  lateral  tension 
or  stretching,  normal  faults  are  formed.* 

SECTION  2.  —  MINERAL  VEINS. 

All  rocks,  but  especially  metamorphic  rocks  in  mountain-regions, 
are  seamed  and  scarred  in  every  direction,  as  if  broken  and  again 
mended,  as  if  wounded  and  again  healed.  All  such  seams  and  scars, 
of  whatever  nature  and  by  whatever  process  formed,  are  often  called 
by  the  general  name  of  veins.  It  is  better,  however,  that  dikes  and  so- 
called  granite-veins,  or  all.  cases  of  fissures  filled  at  the  moment  of 
formation  by  igneous  injection,  should  be  separated  from  the  category 
of  veins.  True  veins,  then,  are  accumulations,  mostly  in  fissures,  of 
certain  mineral  matters  usually  in  a  purer  and  more  sparry  form  than 
they  exist  in  th«  rocks.  The  accumulation  has  in  all  cases  taken  place 
subsequently  to  the  formation  of  the  fissure,  and  by  a  slow  process. 

Kinds.  —  Thus  limited,  veins  are  of  three  kinds  :  Veins  of  segrega- 
tion, veins  of  infiltration,  and  great  fissure-veins.  These  three,  how- 
ever, graduate  into  each  other  in  such  wise  that  it  is  often  difficult  to 
determine  to  which  we  must  refer  any  particular  case.  Some  writers 
make  many  other  kinds,  but  these  may  be  regarded  as  intermediate 
varieties. 

1.  Veins  of  Segregation.  —  In  these  the  vein-matter  does  not  differ 
greatly  from  the  inclosing  rock.     Such  are  the  irregular  lines  of  granite 
in  granite,  the  lines  differing  from  the  inclosing  rock  only  in  color  or 
texture  ;  also  irregular  veins  of  feldspar  in  granite  or  in  gneiss.     Under 
the  same  head  belong  also  the  irregular  streaks,  clouds,  and  blotches,  so 
common  in  marble.     In  these  cases  there  seems  to  be  no  distinct  line  of 
separation  between  the  vein  and  the  inclosing  rock  —  no  distinct  wall  to 
the  vein.     The  reason  is,  these  veins  are  not  formed  by  the  filling  of  a 
previously-existing  fissure,  but  by  the  segregation  of  certain  materials, 
in  certain  spots  and  along  certain  lines,  from  the  general  mass  of  the 
rock,  either  when  the  latter  was  in  plastic  condition  from  heat  and 
water,  or  else  by  means  of  percolating  water,  somewhat  as  concretions 
of  lime,  clay,  iron-ore,  and  flint,  are  formed  in  the  strata  (p.  188). 

2.  Veins  of  Infiltration.  —  Metamorphic  rocks  have,  probably  in  all 
cases,  been  subjected  to  powerful  horizontal  pressure.     Besides  the  wide 
folds  into  which  such  rocks  are  thus  thrown  and  the  great  fissures  thus 
produced,  the  strata  are  often  broken  into  small  pieces  by  means  of  the 

*  Reade  has  shown  (Origin  of  Mountains,  chap,  viii)  that  crust-blocks  formed  by  ten- 
sion and  resting  on  any  kind  of  yielding  foundation,  whether  solid  or  liquid,  would  settle 
so  as  to  form  normal  faults.  It  is  probable,  therefore,  tint  smaller  faults  of  this  kind 
may  be  formed  without  a  sub-crust  liquid. 


MINERAL   VEINS.  235 

squeezing  and  crushing.  The  small  fissures  thus  produced  are  often 
filled  by  lateral  secretion  from  the  walls,  or  else  by  slowly-percolating 
waters  holding  in  solution  the  more  soluble  matters  contained  in  the 
rocks.  The  process  is  similar  to  the  filling  of  cavities  left  by  imbedded 
organisms  (p.  193),  and  still  more  to  the  filling  of  vapor-blebs  in  traps 
and  lavas,  and  the  formation  of  agates  and  carnelian  amygdules  (p. 
215).  In  veins  of  this  kind,  therefore,  a  beautiful  ribbon-structure  is 
often  produced  by  the  successive  deposition  of  different-colored  mate- 
rials on  the  walls  of  the  fissure.  Veins  of  this  kind  also,  since  they 
are  the  filling  of  a  previously-existing  fissure,  have  distinct  walls.  The 
filling  consists  most  commonly  of  silica  or  of  carbonate  of  lime.  Gash- 
veins  of  authors  are  probably  larger  veins  of  this  kind. 

3.  Fissure-  Veins. — These  are  fillings  of  the  great  fissures  produced 
by  movements  of  the  earth's  crust.  When  these  fissures  are  filled  at 
the  time  of  formation  by  igneous  injection,  they  are  called  dikes  ;  but 
if  subsequently  with  mineral  matter,  by  a  different  process,  to  be  dis- 
cussed hereafter,  they  are  fissure-veins.  These  veins,  therefore,  like 
dikes,  outcrop  over  the  surface  of  the  country  often  for  many  miles, 
fifty  or  more.  Like  dikes,  also,  they  are  often  many  yards  in  width,  and 
extend  to  unknown,  but  certainly  very  great,  depths.  Like  dikes  and 
fissures,  also,  they  occur  in  parallel  systems. 

Characteristics. — The  most  obvious  characteristics  of  the  veins  of 
this  class  are  their  size,  their  continuity  for  great  distances  and  to 
great  depths,  and  their  occurrence  in  parallel  systems.  As  the  vein  is 
a  filling  of  a  previously-existing  fissure,  the  distinction  between  the 
vein  and  the  wall-rock  is  usually  quite  marked.  In  many  cases,  in 
fact,  the  vein-filling  is  separated  from  the  wall-rock  by  a  layer  of  tena- 
cious, clayey  matter  called  a  selvage.  The  selvage  is  probably  formed 
by  decomposition*  of  the  wall-rock  in  immediate  contact  with  the  vein, 
by  circulating  water.  The  contents  of  fissure-veins  are  also  far  more 
varied  than  those  of  other  classes. 

Metalliferous  Veins. — f>ome  metals,  particularly  iron,  occur  prin- 
cipally in  great  beds}  being  accumulated  by  a  process  already  described 
(p.  144).  Others,  especially  lead,  often  accumulate  in  flat  cavities  be- 
tween the  strata,  especially  of  limestone.  But  most  metals  occur  in 
veins.  All  the  kinds  of  veins  mentioned  above  may  contain  metals, 
but  the  segregative  veins  are  usually  too  irregular  and  uncertain,  and 
the  infiltrative  veins  too  small,  to  be  profitable.  (True,  profitable  metal- 
liferous veins  are  almost  always  great  fissure-veins.}  We  will  speak, 
therefore,  principally  of  these,  and  the  further  description  of  fissure- 
veins  is  best  undertaken  under  this  head. 

Contents.— ^The  contents  of  metalliferous  veins  are  of  two  general 
kinds,  viz.,  vein-stuffs  and  ores.  The  principal  vein-stuffs  are  quartz, 
carbonate  of  lime  (calc-spar),  carbonate  of  baryta,  carbonate  of  iron, 


236 


STRUCTURE   COMMON  TO    ALL   ROCKS. 


sulphate  of  baryta  (heavy  spar),  and  fluoride  of  calcium  (fluor-spar). 
By  far  the  most  common  of  these  is  quartz,  and  next  is  calc-spar. 
Often,  however,  the  vein-stuff  is  an  aggregate  of  minerals  forming  a 
true  rock.  Nearly  the  whole  of  a  vein  consists  usually  of  vein-stuff. 
The  ore  exists  in  comparatively  small  quantities,  sometimes  forming  a 
central  rib  or  sheet,  as  if  deposited  last  (Fig.  208.  a  b) ;  sometimes  in 
irregular  isolated  masses  called  bunches  or  pockets,  or  in  small  strings, 
or  grains,  irregularly  scattered  through  the  vein-stuff  and  extending 
often  a  little  way  into  the  wall-rock. 

The  chemical  forms  in  which  metals  occur  are  very  various;  some- 
times they  occur  as  pure  metal  (as  always  in  the  case  of  gold  and  plat- 
inum, and  sometimes  in  the  case  of  silver  and  copper),  but  more  com- 
monly in  the  form  of  metallic  sulphides,  metallic  oxides,  and  metallic 
carbonates.  Of  these  the  metallic  sulphides  are  by  far  the  most  com- 
mon. It  is  worthy  of  remark  that  all  these  forms  are  comparatively 
very  insoluble.  The  same  is  true  of  the  vein-stuffs. 

Ribboned  Structure. — The  ribboned  or  banded  structure,  already 
spoken  of  under  Veins  of  Infiltration,  is  very  commonly  found  in  great 
fissure-veins.  This  structure  is  as  characteristic  of  veins  as  the  colum- 
nar structure  is  of  dikes.  The  layers  on  the  two  sides  usually  corre- 
spond to  each  other  (Fig.  208) ;  sometimes  the  successive  layers  are  of 
different  color,  giving  rise  to  a  beautiful,  striped  appearance.  Some- 
times the  successive  layers  on  both  sides  are  of  different  materials,  as 
in  Fig.  209,  in  which  the  central  rib,  d,  is  galena,  and  a  a,  b  b,  c  c,  are 


FIG.  210. 


successive  layers  of  quartz,  fluor,  and  baryta.  Sometimes,  in  cases  of 
quartz-filling,  the  layers  are  agate,  except  the  center,  which  is  filled  up 
with  a  comb  of  interlocking  crystals,  as  in  Fig.  210.  The  same  occurs 
often  in  amygdules,  the  last  filling  being  crystalline.  Sometimes  there 
is  evidence  of  successive  openings  and  fillings,  as  in  Fig.  211,  where  a 
represents  quartz-crystals,  interlocking  in  the  center  and  based  on  agate 
layers,  b  b,  while  c  represents  quartz  with  disseminated  copper  pyrites. 
In  this  case  it  seems  probable  that  1  and  2  were  the  walls  when  the 
agate  and  quartz-filling  took  place,  and  that  afterward  the  fissure  was 
reopened  along  2,  so  that  the  walls  became  2  and  3,  and  the  new  fissure 


MINERAL   VEIXS. 


237 


thus  formed  was  filled  with  cupriferous  quartz.  The  same  is  well  shown 
in  Fig.  212,  where  «,  #,  c,  d,  e,f,  are  successive  quartz-combs,  separated 
by  2,  3,  4,  5,  6,  which  are  clay  selvages,  and  therefore  old  walls. 


I     a      b 


FIG.  212. 

Irregularities. — Although  more  regular  than  other  kinds,  yet  fis- 
sure-veins are  also  often  quite  irregular — sometimes  branching,  some- 
times narrowing  or  pinching  out  in  some  parts  and  widening  in  others 
(Fig.  213),  sometimes  dividing  and  again  coming  together,  and  thus 
inclosing  a  portion  of  the  wall-rock  (Fig.  214).  Such  an  inclosed  mass 


FIG.  213.— Irregularities  in  Veins. 


FIG.  214.— Irregularities  in  Veins. 


of  country  rock  in  the  midst  of  a  vein  is  called  a  "Jiorse."  Many  of 
these  irregularities  are  probably  the  result  of  movements  after  the  fis- 
sure was  formed,  or  even  after  it  was  filled.  Thus,  if  a  b  c  d  (Fig.  213) 
be  one  wall  of  an  irregular  vein,  then  it  is  probable  that  a'  b'  c'  d'  was 
the  original  position  of  this  wall ;  but,  before  it  was  filled,  it  slipped 
up  to  its  present  position.  Or,  an  open  fissure  may  pinch  together  in 
places  by  what  is  called  creeping  of  the  strata  of  the  wall,  i.  e.,  a  mash- 
ing and  filling  in  by  pressure  of  superincumbent  weight.  Again, 
movements  may  reopen  a  fissure  after  it  is  filled.  In  such  cases,  if  the 
adhesion  of  the  filling  to  the  wall  is  strong,  portions  of  the  wall-rock 
are  torn  away ;  and,  if  a  second  filling  takes  place,  a  "  horse  "  is  formed. 
Thus  a  a  a  and  l>  b  b  (Fig.  214)  represent  the  two  original  walls  of  an 
irregular  vein ;  but  subsequent  movement  reopened  the  fissure  to  b'  V  b' 


238 


STRUCTURE  COMMON  TO  ALL  ROCKS. 


and  tore  away  the  horse  JJ,  after  which  the  vein  was  again  filled.  Also 
crust-movements  may  form  not  only  a  single  clean  fissure,,  but  some- 
times many  small,  irregular  fractures,  with  wall-rock  between.  The 
filling  of  these,  form  irregular  veins  in  which  vein-stuff  is  often  inex- 
tricably mingled  with  country  rock.  The  vein  may  thus  be  filled  with 
a  troop  of  horses.  Finally,  in  some  rocks,  especially  limestone,  percolat- 
ing waters  will  hollow  out  passages  in  the  most  irregular  way.  These 
also  may  become  filled  with  vein-stuff  and  give  rise  to  irregular  veins. 
Veins,  of  course,  usually  intersect  the  strata ;  but  in  some  cases 
where  strata-planes  are  highly  inclined  the  opening  is  between  these 
planes,  and  the  veins  are,  therefore,  conformable  with  them. 

Age. — The  relative  age  of  veins  in  the  same  region  is  determined 
in  the  same  way  as  that  of  dikes,  viz.,  by  the  manner  in  which  they 

intersect  each  other;  the  in- 
tersecting vein  being,  of  course, 
younger  than  the  intersected 
vein.  Thus  in  Fig.  215,  which 
is  a  section  of  a  hill-side  in 
Cornwall,  it  is  evident  that  the 
tin  vein,  «,  is  the  oldest,  since 
it  is  intersected  and  slipped  by 
all  the  others.  The  copper- 
vein,  #,  is  older  than  the  clay- 
filled  fissure,  c.  There  is  a 
fourth  fissure,  d,  newer  than 
«,  but  its  relation  to  #  and  c  is  not  shown  in  the  section. 

The  absolute  age  of  fissure-veins,  or  the  geological  period  in  which 
the  fissure  was  formed,  can  only  be  determined  by  the  stratified  rocks 
through  which  it  breaks.  The  lead-veins  of  Cornwall  (b  b,  Fig.  217) 
break  through  the  Cretaceous.  Their  fissures  were  probably  formed  by 
the  changes  or  oscillations  which  closed  the  Cretaceous  and  inaugurated 
the  Tertiary  period.  '  The  auriferous  veins  of  California  break  through 
the  Jurassic  ;  and,  as  there  are  good  reasons  for  believing  that  the  Sierras 
were  formed  at  the  end  of  the  Jurassic,  it  is  probable  that  these  fissures 
were  formed  at  that  time  by  the  foldings  of  the  strata  consequent  upon 
the  pushing  up  of  this  range.  The  filling,  of  course,  was  a  slow,  sub- 
sequent operation,  but  commenced  then. 

Surface-Changes. — Mineral  veins  seldom  or  never  outcrop  on  the 
surface  in  the  condition  we  have  described  them.  On  the  contrary, 
there  are  certain  changes  which  they  undergo  through  the  influence  of 
atmospheric  agencies,  which  render  their  appearance  along  their  out- 
crop quite  different  from  that  of  the  same  vein  at  some  depth  below. 
A  knowledge  of  these  changes  is,  of  course,  of  the  greatest  practical 
importance.  They  are,  however,  extremely  various,  differing  not  only 


FIG.  215. 


MINERAL   VEINS. 


239 


according  to  the  metallic  contents,  but  also  according  to  the  nature  of 
the  vein-stuffs,  and  therefore  must  be  learned  by  observation  in  each 
country.  We  will  give  three  of  the  most  constant  as  illustrations. 

Cupriferous  Veins.— The  original  form  in  which  copper  seems  to 
exist  in  veins  is  copper  pyrites,  a  double  sulphide  of  copper  and  iron 
{CuFeSJ.  Now,  along  the  back  or  outcrop  of  copper-veins,  to  a  depth 
of  thirty  to  sixty  feet,  the  vein  usually  contains  no  copper  at  all,  but 
consists  of  vein-stuff  (more  or  less  changed,  according  to  its  nature), 
among  which  are  scattered  masses  of  a  dark  reddish  or  brownish 
hydrated  peroxide  of  iron,  in  a  light,  spongy  condition.  This  peculiar 
form  of  peroxide  of  iron,  so  characteristic  of  the  outcrop  of  copper- 
veins,  is  called  by  the  Cornish  miners  gossan,  and  b^  the  German  and 
French  miners  iron  hat  (eiserner  hut ;  chapeau  defer).  Below  the  in- 
fluence of  atmospheric  agencies  the  vein  is  in  its  original  condition,  i.  e., 
consists  of  vein-stone  containing  disseminated  masses  of  copper  pyrites. 
Just  at  the  junction  of  the  changed  with  the  unchanged  vein — i.  e,, 
running  along  the  back  of  the  vein  at  a  depth  varying  from  thirty  to 
sixty  feet — occur  rich  accumulations  of  copper,  as  native  copper,  red 
and  black  oxides  of  copper,  green  and  blue  carbonates  of  copper,  etc. 
These  facts  are  illustrated  by  Fig.  216,  which  is  a  section  of  the  Duck, 

town  mines  of  Tennessee.  The 
irregular  line,  s  s,  is  the  out- 
line of  a  hill,  along  the  crest  of 
which  the  vein  outcrops ;  the 
part  b  consists  almost  wholly 
of  gossan,  with  only  small 
masses  of  quartz- vein  stuff ;  a 
is  the  rich  accumulation  of 
copper  ore,  here  about  two  or 
three  feet  thick  ;  and  c  is  the 
unchanged  vein,  consisting  of 
vein-stuff,  inclosing  arsenical 

FIG.  216.— Ducktown  (Tennessee)  Copper  Vein,  show-    -rvrr-Una       ~A    , 

ing  Surface-Changes  (after  Safford).  PFltes»  and    Copper  pyrites   in 

very  large  quantities. 

These  phenomena  may  be  explained  as  follows :  There  can  be  no 
doubt  that  the  gossan  represents  copper  pyrites,  from  which  the  copper 
has  been  entirely  washed  out,  leaving  the  iron  in  an  oxidized  condition. 
Thus  the  whole  of  the  copper  from  ~b  (and  probably  from  much  more 
than  b,  for  the  process  of  denudation  has  gone  on  pari  passu  with  the 
process  of  leaching)  has  been  leached  out  and  accumulated  at  a.  Fur- 
ther, it  is  probable  that  the  process  was  as  follows :  When  copper 
pyrites  is  exposed  to  moist  air  it  slowly  oxidizes  into  sulphates  of  iron 
and  copper  (CuFeS8+80=FeS04+CuS04).  The  iron  sulphate  (prob- 
ably assisted  by  reaction  with  alkaline  or  earthy  carbonates)  quickly 


240  STRUCTURE  COMMON   TO  ALL   ROCKS. 

passes  into  ferric  oxide  and  is  left  in  a  spongy  condition,  while  the 
copper  sulphate  is  carried  downward.  This  much  seems  certain,  but, 
by  what  subsequent  process  the  copper  takes  all  the  forms  actually 
found  at  a,  is  little  understood,  although  it  is  probable  that  the  car- 
bonate is  produced  by  the  reaction,  on  the  sulphate,  of  waters  contain- 
ing alkaline  carbonate  or  bicarbonate  of  lime.* 

Plumbiferous  Veins. — The  natural  or  original  form  in  which  lead 
occurs  in  veins  is  sulphide  of  lead,  or  galena.  But  along  the  backs  or 
outcrops  of  lead- veins  it  is  found  more  commonly  as  carbonate.  The 
explanation  seems  to  be  as  follows  :  Lead  occurs  mostly  in  veins  inter- 
secting, or  in  sheets  between,  strata  of  limestones.  It  is  probable  that 
the  galena  (PbS)  is  oxidized  by  meteoric  agencies  and  becomes  sulphate 
(PbSOJ,  and  then  the  sulphate,  by  reaction  with  the  carbonate  of  lime 
derived  from  the  wall-rock  or  from  the  calc-spar  of  the  vein-stuif,  be- 
comes carbonate,  thus:  PbS04+OaC03=PbC08+CaS04.  In  proof 
of  this  process  it  is  stated  f  that  galena,  thrown  out  of  the  old  mines  of 
Derbyshire  among  rubbish  of  limestone,  has  all,  in  the  course  of  ages, 
been  changed  into  carbonate.  Moreover,  it  is  not  uncommon  to  find 
in  lead  veins  masses  of  sulphide  changed  on  the  outside  into  carbonate. 

Auriferous  Quartz- Veins. — Gold  is  found  either  in  quartz-veins,  in- 
tersecting metamorphic  slates  (quartz-mines)  or  in  gravel-drifts  in  the 
vicinity  of  these  (placer-mines).  Originally  it  existed  in  the  quartz- 
veins  usually  associated  with  metallic  sulphides,  particularly  the  sul- 
phide of  iron  (pyrites).  If  the  pyrites  be  dissolved  in  nitric  acid,  the 
gold  is  left  as  minute  threads  and  crystals.  Evidently,  therefore,  it  exists 
in  minute  threads  and  crystals  scattered  through  the  pyrites.  Now, 
when  such  a  vein  is  exposed  to  meteoric  agencies,  the  pyrites  is  oxi- 
dized, partly  as  soluble  sulphate,  and  carried  away,  and  partly  as  insol- 
uble reddish  peroxide,  which  remains.  J  The  quartz-vein  stone  is,  there- 
fore, left  in  a  honey-comb  condition  by  the  removal  of  the  pyrites,  and 
more  commonly  stained  of  a  rusty  color  by  the  peroxide.  Among  the 
cells  of  this  rusty  cellular  quartz  the  gold  is  found  in  minute,  sharp 
grains,  evidently  left  by  the  removal  of  the  pyrites.  Hence,  in  an 
auriferous  quartz- vein,  along  the  outcrop  to  a  depth  of  thirty  to  sixty 
feet  (i.  e.,  as  far  as  meteoric  agencies  extend)  gold  is  found  free  in 
small  grains  among  the  cellular  quartz  ;  but  below  the  reach  of  these 
agencies  it  is  inclosed  in  the  undecomposed  pyrites. 

Placer-Mines. — If  a  mountain-slope,  along  which  outcrop  auriferous 
quartz-veins,  be  subjected  to  powerful  erosion  by  water-currents,  then 

*  Bischof,  Chemical  and  Physical  Geology,  vol.  iii,  p.  509. 

f  De  la  Beche,  Geological  Observer,  p.  794. 

\  Probably  the  iron  sulphide  is  oxidized  to  the  condition  of  sulphate,  then  reduced  to 
carbonate  by  water  containing  alkaline  cai'bonate  or  bicarbonate  of  lime,  and  lastly  per- 
oxidized  by  exchanging  carbonic  acid  for  oxygen  (Bischof). 


LAWS  AFFECTING   METALLIFEROUS  VEINS.  241 

in  the  stream-beds  will  be  found  gravel-drifts,  composed  partly  of  the 
country  rock  and  partly  of  the  quartz  vein-stone.  Among  the  gravel 
will  be  found  particles  of  gold,  washed  out  from  the  upper  parts  of  the 
veins.  By  the  sorting  power  of  water  the  heavy  gold  particles  are  apt 
to  accumulate  mostly  near  the  bed  of  the  gravel-deposit  (bed-rock). 
These  gravel-deposits  are  the  placers.  In  these,  the  gold-particles,  like 
the  stone-fragments,  are  always  rounded  and  worn  by  attrition. 

Some  Important  Laws  affecting  the  Occurrence  and  the  Richness  of 
Metalliferous  Veins. 

1.  Metalliferous  veins  occur  mostly  in  disturbed  and  highly-meta- 
morphic  regions,  where  the  strata  are  tilted,  and  folded,  and  metamor- 
phosed.    The  tilting  and  folding  are  necessary  to  the  formation  of  fis- 
sures ;  and  the  conditions  under  which  metamorphism  takes  place  seem 
necessary  for  the  subsequent  filling  with  mineral  matter.     Mineral  veins, 
therefore,  occur  mostly  in  mountain  regions^  and  in  the  vicinity  of  more 
<or  less  obvious  evidences  of  igneous  agency.     Lead- veins  seem  to  be  an 
exception  to  this  rule.     They  are  often  found  in  undisturbed  regions 
where  the  rocks  are  entirely  unchanged.     The  rich  lead-mines  of  Illi- 
nois, Iowa,  and  Missouri,  are  notable  examples,  the  country  rock  being 
horizontal,  fossiliferous  limestones  of  the  Palaeozoic  era. 

2.  Metalliferous  veins  occur  mostly  in  the  older  rocks.     In  Great 
Britain,  for  example,  no  profitable  veins  occur  above  the  Trias.     This 
rule,  which  was  regarded  as  of  great  importance  by  the  older  geologists, 
is  not  so  regarded  now.    There  seems  to  be  no  close  connection  between 
the  occurrence  of  metalliferous  veins  and  simple  age  alone ;  the  con- 
nection is  rather  with  metamorphism.    Metamorphism,  as  we  have  seen, 
(p.  219),  is  most  common  in  the  older  rocks,  and  becomes  more  and 
more  exceptional  as  we  pass  upward.     The  occurrence  of  metalliferous 
veins  follows  the  same  law.     But  when  the  newer  rocks  are  metamor- 
phic,  they  are  as  likely  to  contain  veins  as  are  rocks  of  the  older  series. 
The  metalliferous  veins  of  California  occur  in  Jurassic,  Cretaceous,  and 
even  Tertiary  strata ;  but  these  strata  are  there  highly  metamorphic,  and 
strongly  folded.     In  Bohemia,  also,  and  elsewhere,  metalliferous  veins 
occur  in  the  higher  series  (Phillips's  Geology,  p.  549). 

3.  Parallel  veins  are  apt  to  have  similar  metallic  contents,  while  veins 
running  in  different  directions  (unless  sometimes  at  right  angles)  are  apt 
to  contain  different  metallic  contents.     Thus,  the  nearly  east-and-west 
lodes  of  Cornwall,  a  a  a  and  c  c  (Fig.  217),  contain  tin  and  copper, 
while  the  north-and-south  courses,  ft  #,  contain  lead  and  iron.    The  au- 
riferous veins  of  California  are  parallel  to  each  other  and  to  the  Sier- 
ras, except  a  few  smaller  ones,  which  are  at  right  angles  to  these.    The 
reason  of  this  rule  is,  that  parallel  fissures  belong  to  the  same  system, 
and  were  therefore  formed  at  the  same  time,  broke  through  the  same 

16 


242 


STRUCTURE  COMMON  TO  ALL  ROCKS. 


strata,  and  were  filled  under  similar  conditions,  and  therefore  with  the 
same  materials ;  while  fissures  running  in  different  directions  (unless  in 
some  cases  at  right  angles,  p.  228)  were  probably  formed  at  different 


FIG.  217.— Map  of  Cornwall:  a  and  c,  tin  and  copper;  5,  lead  and  iron. 

broke  through  different  strata,  and  were  filled  under  different 
conditions.  Thus,  the  east-and-west  veins  of  Cornwall,  a  a,  are  pre- 
triassic ;  the  north-east  and  south-west  veins,  c  c,  break  through  the 
Trias,  and  are  therefore  post-triassic,*  while  the  north-and-south  veins 
break  through  the  Cretaceous.  The  auriferous  veins  of  California  all 
break  through  the  Jurassic ;  they,  or  their  fissures,  were  probably  pro- 
duced at  the  same  time,  viz.,  at  the  time  of  pushing  up  of  the  Sierras. 

4.  A  change  of  country  rock  of  an  outcropping  vein  is/ apt  to  deter- 
mine some  change,  either  in  the  contents  or  in  the  richness  of  the  vein. 
Nevertheless,  there  is  not  that  close  connection  between  the  nature  of 
the  country  rock  and  the  vein-contents  which  obtains  in  infiltrative 
veins.    The  reason  is,  that  infiltrative  veins  derive  their  contents  entirely 
from  the  wall-rock  on  either  side,  while  fissure- veins  derive  their  contents 
from  all  the  strata  through  which  they  break,  even  to  great  depths,  and 
especially  from  the  deeper  strata.    The  nature  of  the  surface  or  country 
rock  is,  therefore,  only  one  factor,  determining  the  vein-contents. 

5.  Metallic  veins  are  usually  richer  near  their  point  of  intersection 
with  granite  or  with  an   igneous  dike,  especially  if  the   strata   have 
suffered  metamorphism.     This  shows  the  influence  of  such  heat  as  is 
present  in  metamorphism,  in  determining  the  metallic  contents. 

•  6.  If  two  veins  cross  each  other,  especially  if  at  small  angle,  one  or 
both  are  apt  to  be  richer  at  the  point  of  crossing.  No  sufficient  reason 
has  been  given  for  this  law.  It  is  probably  due  to  the  reaction  of 
waters  bearing  different  materials  circulating  in  the  two  fissures. 

*  De  la  Beche,  Geological  Observer,  p.  757. 


THEORY   OF   METALLIFEROUS   VEINS.  243 

7.  Since  veins  are  the  fillings  of  fissures,  they  are  often  slipped  by 
each  other  or  by  dikes  or  by  simple  unfilled  fissures.    If  a  metalliferous 
vein  is  thus  slipped,  according  to  the  law  of  slips  already  given  (p.  231) 
the  foot- wall  of  the  vein  has  usually  gone  upward,  and  the  hanging  wall 
dropped  downward.     The   great  importance  of  this  law  in  practical 
mining  is  sufficiently  obvious.     All  the  slips  of  Fig.  215,  except  that 
made  by  the  fissure  c,  follow  this  law. 

8.  The  surface-indications  are  to  be  learned  by  attentive  observa- 
tion in  each  case.     We  have  already  given  these  in  the  case  of  copper, 
lead,  and  gold. 

TJieory  of  Metalliferous  Veins. 

Our  knowledge  of  the  conditions  under  which,  and  the  chemical  pro- 
cess by  which,  fissures  have  been  filled  with  mineral  matter,  is  yet,  un- 
fortunately, very  imperfect.  Many  vague  and  crude  theories  have  been 
proposed.  Some  have  supposed  that  they  have  been  filled  in  the  man- 
ner of  dikes  and  granite  veins,  by  igneous  injection ;  others,  that  these 
fissures,  opening  below  into  the  regions  of  incandescent  heat,  have  been 
filled  by  sublimation,  i.  e.,  by  vaporization  of  certain  materials  and 
their  condensation  in  the  fissures  above.  Some  suppose  that  electric 
currents,  such  as  are  known  by  observation  to  traverse  certain  veins, 
have  been  the  chief  agents  in  the  transference  and  accumulation  of  the 
mineral  matter.  These  three  theories  may  be  dismissed  as  being  un- 
tenable or  else  as  too  hypothetical.  Still  others  have  thought  that  great 
fissures  have  filled  in  the  same  manner  as  the  smaller  fissures,  and  cav- 
ities of  every  kind  found  in  the  rocks,  viz.,  by  infiltration  of  soluble 
matters  from  the  fissured  rocks.  There  is  certainly  considerable  anal- 
ogy between  small  infiltrative  veins  and  great  fissure- veins  in  their 
mode  of  formation;  yet  there  is  a  decided  difference.  The  fillings 
of  infiltrative  veins  are  derived,  in  each  part,  entirely  from  the  bound- 
ing rock  on  either  side.  The  fissure  is  filled  by  a  lateral  secretion 
from  its  walls ;  the  broken  rocks  heal  themselves  "  by  first  intention  " 
by  means  of  a  plasma  oozing  from  the  sides.  But  great  fissure- veins 
derive  their  contents  in  each  part  from  all  the  strata  to  great  depths, 
and  especially  from  the  deeper  strata.  Hence  the  contents  of  these 
veins  are  far  more  varied. 

Outline  of  the  Most  Probable  Theory.— The  contents  of  mineral 
veins  seem  to  have  been  deposited  from  hot  alkaline  solutions  coming 
up  through  fissures ;  in  other  words,  from  hot  alkaline  springs.  We 
will  attempt  to  show  this  first  for  the  vein-stuffs,  especially  quartz,  and 
then  for  the  metallic  ores,  especially  the  metallic  sulphides. 

Vein-Stuffs. — 1.  They  were  deposited  from  solutions,  (a.)  The  rib- 
bon-structure and  the  interlocked  crystals  (Figs.  210,  211)  suggest  at 
once  successive  deposition  from  solution,  especially  as  a  similar  structure 
occurs  in  the  fillings  of  cavities  of  all  kinds,  which  could  not  have  been 


244  STRUCTURE   COMMON  TO   ALL  ROCKS. 

filled  in  any  other  way.  (#.)  Quartz  is  by  far  the  most  common  of  all 
vein-stuffs.  Now,  as  already  explained  (p.  224),  there  are  two  varieties 
of  silica — one  having  a  specific  gravity  of  2'2,  the  other  2-6.  The  dry 
way  produces  only  quartz-glass,  which  has  a  specific  gravity  of  2*2, 
while  the  variety  of  specific  gravity  2-6,  or  true  quartz,  can  not  be 
formed  except  by  the  humid  way.*  In  fact,  this  variety,  as  far  as  we 
know,  is  always  produced  by  slow  deposition  from  solution.  Now,  the 
quartz  of  veins  is  always  the  variety  2-6,  and  therefore  was  produced 
by  slow  deposit  from  solution.  The  beautiful  crystals  so  often  found 
in  veins  could  be  produced  in  no  other  way.  (c.)  We  have  already 
seen  (p.  224)  that  fluid  cavities  are  a  proof  of  formation  by  humid  pro- 
cess. Now,  such  fluid  cavities  are  especially  abundant  in  vein-stuffs 
generally.  They  are  best  seen  in  quartz- vein  stuffs,  because  of  their 
transparency,  (d.)  Not  only  quartz  but  many  other  minerals  found 
among  vein-stuffs  are  of  such  nature  that  it  is  difficult  or  impossible  to 
understand  how  they  could  have  been  formed  except  by  the  humid 
way,  as  they  will  not  stand  fusing  temperature. 

2.  The  solutions  were  hot.     (a.)  Fissures  running  deep  into  the 
interior  of  the  earth  could  hardly  remain  empty  of  water.     But  from 
their  great  depth  the  contained  waters  must   be   hot.     The  solvent 
power  of  water,  when  heated  to  high  temperature  under  pressure,  is 
well  known.     Scarcely  any  substance  wholly  resists  it.     (b.)  The  fluid 
cavities  found  in  quartz  and  other  vein-stuffs  are  not '  usually  entirely 
filled,  but  contain  a  small  vacuous  space.     Such  a  vacuous  space  indi- 
cates (p.  225)  that  the  inclosed  liquid  was  at  high  temperature  at  the 
time  of  being  inclosed,  and  has  since  contracted  on  cooling.     By  heat- 
ing the  mineral  until  the  cavity  fills  and  the  vacuous  space  disappears, 
we  ascertain  the  temperature   of  deposit.    Now,  by  this  process  the 
temperature  of  deposit  of  vein-minerals  has  been  ascertained  to  vary 
from  ordinary  temperatures  even  up  to  300°  and  350°.f     (c.)  The  in- 
variable association  of  metalliferous  veins  with  metamorphism  demon- 
strates the  agency  of  heat. 

3.  TJie  solutions  were  alkaline. — Alkaline  carbonates  and  alkaline 
sulphides  are  the  only  natural  solvents  of  quartz,  the  commonest  of 
vein-stuffs.     Moreover,  when  these  waters  contain  excess  of  carbonic 
acid,  as  is  almost  always  the  case,  they  dissolve  also  the  carbonates  of 
lime,  baryta,  iron,  etc.,  the  next  most  common  forms  of  vein-stuffs.    In 
California  and  Nevada  such  hot  alkaline  carbonate  and  alkaline  sul- 
phide springs  abound,  and  are  daily  depositing  silica  (quartz)  and  car- 
bonates of  lime  and  of  iron,  and  even  in  some  cases  filling  fissures. 

*  Recently  under  peculiar  conditions  crystallized  quartz  of  specific  gravity  2*6  has  been 
formed  by  dry  fusion. — American  Journal  of  Science,  vol.  xvi,  p.  155,  1878. 
f  Sorby,  Quarterly  Journal  of  the  Geological  Society,  vol.  xiv,  p.  453,  et  scq. 


THEORY   OF  METALLIFEROUS  VEINS.  245 

Metallic  Ores.  —  There  seems  no  reason  to  doubt,  then,  that,  in  most 
cases  at  least,  vein-stuffs  have  been  deposited  from  hot  alkaline  solu- 
tions. Now,  it  is  evident,  from  their  intimate  association  with  the  vein- 
stuffs,  that  the  metallic  ores  must  have  been  deposited  from  the  same 
solution.  The  exact  nature  of  the  solvent  and  the  chemical  reaction 
is  still  very  doubtful.  We  may  imagine  many  by  either  of  which  the 
deposit  might  take  place:  1.  Metallic  sulphides  are  by  far  the  most 
common  form  of  ore,  and  even  when  other  forms  exist  we  may  in  many 
cases  trace  them  to  sulphide  as  their  original  form  (p.  239,  et  seq.).  But 
metallic  sulphides  are  slightly  soluble  in  alkaline  sulphides,  and  these 
latter  are  often  found  associated  with  alkaline  carbonates  in  hot  springs 
(solfataras),  as  in  California  and  elsewhere.  Such  waters  would  hold 
in  solution  silica,  carbonates  of  lime,  etc.,  and  metallic  sulphides,  and, 
coming  up  through  fissures,  would  deposit  them  both  by  cooling  and  by 
relief  of  pressure.  Or,  2.  Alkaline  carbonate  waters  holding  in  solu- 
tion silica  and  lime  carbonate  for  vein-stone,  and  also  containing  alka- 
line sulphide,  meeting  and  mingling  in  the  same  fissure  with  other  waters 
containing  metallic  sulphates,  by  reaction  would  precipitate  metallic 
sulphides  (NaS-f  MS04=NaS04+MS).  This  seems  to  be  the  reaction 
by  which  the  inky  waters  of  some  of  the  hot  springs  of  the  California 
geysers  are  formed.  Or,  3.  The  alkaline  carbonates  still  remaining  for 
vein-stone,  metallic  sulphates,  in  solution  in  the  same  waters  with 
organic  matter,  would  be  reduced  to  the  form  of  metallic  sulphide, 
which,  being  insoluble,  would  be  deposited.*  Or,  4.  Alkaline  sulphide 
waters  holding  metallic  sulphides  and  organic  matters  in  solution  —  the 
acids  of  organic  decomposition  (humus  acicts)  would  neutralize  the 
alkalinity  and  deposit  the  metallic  sulphide.  For  greater  clearness  we 
annex  a  table  expressing  these  processes  : 

l.Alk.S  +  MS  in  sol"  deposit  MS  by  cooling. 
AH  no      unr*       I  2-  Alk.S  +  MSO4  meeting     "     MS  "    reaction. 
^  «     MS"    reduction. 


4.  Alk.S  +  MS  +  orgc  mat'  insoln  deposit  MSby  neutralization. 

There  are  many  difficulties  in  the  way  of  every  attempt  to  place 
these  reactions  in  a  clear  and  distinct  form,  but  in  spite  of  these  diffi- 
culties there  seems  little  reason  to  doubt  that  great  fissures  have  been 
filled  by  deposit  from  hot  alkaline  waters  holding  various  mineral  sub- 
stances in  solution.  The  more  insoluble  substances  are  deposited  in 
the  vein,  while  the  more  soluble  reach  the  surface  as  mineral  springs. 

*  It  might  at  first  seem  that  there  is  a  chemical  difficulty  in  this  case  —  that  metallic 
sulphate  can  not  coexist  in  solution  with  alkaline  carbonate,  but  would  be  precipitated  as 
metallic  carbonate.  But  it  is  evident  that  this  reaction  would  not  take  place  in  a  weak 
metallic  solution,  in  the  presence  of  excess  of  carbonic  acid,  since  in  this  case  the  metallic 
carbonate  is  soluble. 


246  STRUCTURE   COMMON  TO  ALL   ROCKS. 

This  view  is  powerfully  supported  by  the  phenomena  of  hot  alka- 
line springs  in  California  and  Nevada.  The  Steamboat  Springs,  near 
Virginia  City,  Nevada  (so  called  from  the  periodic  eruption  of  hot 
water  and  steam),  come  up  through  fissures  in  comparatively  recent 
volcanic  rock.  The  waters  are  strongly  alkaline,  and  deposit  silica  in 
abundance.  By  this  deposit  the  fissures  are  gradually  filling  up  and 
forming  veins.  Some  fissures  are  now  partially  and  some  entirely  filled. 
The  ribbon-structure  in  some  cases  is  perfect.  Moreover,  sulphides  of 
several  of  the  metals,  viz.,  iron,  lead,  mercury,  copper,  and  zinc,  have 
been  found  in  the  quartz-vein  stuff.  Here,  then,  we  have  true  metalli- 
ferous veins  forming  under  our  very  eyes.*  So  also  at  Sulphur  Bank, 
Lake  County,  California,  hot  alkaline  sulphide  waters,f  coming  up  from 
beneath,  deposit  both  silica  and  cinnabar  in  small,  irregular  fissures 
and  cavities,  forming  quartz- veins  containing  cinnabar.  The  deposit 
is  so  recent  that  the  silica  is  sometimes  still  in  a  soft,  hydrated  con- 
dition, which  cuts  like  cheese.]; 

After  this  general  discussion  of  the  theory  of  metalliferous  veins, 
we  are  now  in  position  to  state  more  clearly  their  mode  of  formation. 
Meteoric  waters,  circulating  in  the  interior  of  the  earth  in  any  direc- 
tion— downward,  upward,  or  laterally — deposit  slightly  soluble  matters 
in  their  course,  in  cracks,  cavities,  or  great  fissures,  forming  fossil  casts, 
geodes,  amygdules,  infiltration-veins,  and  fissure-veins.  As  to  direction, 
the  up-coming  waters,  especially  in  metamorphic  and  volcanic  regions, 
deposit  most  freely,  and  are  most  metalliferous,  because  they  are  hot  and 
often  alkaline,  and  therefore  most  powerful  solvents,  and,  of  course,  cool 
gradually  on  approaching*the  surface.  But  that  downward  percolating 
waters  may  also  deposit  metallic  ores  is  proved  by  the  fact  that  these 
are  sometimes  found  depending,  like  stalactites,  from  the  roofs  of  cavi- 
ties.* As  to  the  different  kinds  of  veins,  those  of  great  fissures  are 
most  prolific,  because  these  fissures  are  the  highways  of  water  from 
the  heated  depths.  But  every  kind  of  water-way  will  receive  deposits ; 
and,  as  the  kinds  of  these  are  infinitely  various  and  pass  by  insensible 
gradations  into  each  other,  so  also  will  be  the  veins  which  fill  them. 
The  open  fissure  is  the  easiest  and  therefore  the  most  traveled  high- 
way. In  these,  therefore,  we  have  the  most  perfect  type  of  veins,  with 
their  banded  structure  and  their  selvages,  their  great  size  and  conti- 
nuity. But  in  many  cases  crust-movements  produce  only  incipient  fis- 
sures, i.  e.,  a  loosening  of  the  rock-cohesion,  along  planes  affected  with 

*  Arthur  Phillips.  American  Journal  of  Science,  vol.  xlvii,  p.  194;  and  Philosophical 
Magazine,  1872,  vol.  xlii,  p.  401. 

f  The  water  in  this  mine  is  176°  Fahr. — Becker. 

\  Le  Conte,  American  Journal  of  Science,  vol.  xxiv,  p.  23,  1882. 

*  Schmidt,  American  Journal  of  Science,  vol.  xxi,  p.   502,   1881.      Chamberlain's 
Geology  of  Wisconsin,  vol.  iii,  p.  495. 


THEORY  OF  METALLIFEROUS  VEINS.  247 

a  multitude  of  small  cracks,  with  country  rock  between.  These 
loosened  planes  become  also  water-ways,  and,  by  deposit,  form  those 
irregular  veins  so  common  everywhere,  but  especially  in  the  cinnabar- 
veins  of  California.  Or,  again,  crust-movements  may  produce  not 
clean  open  fissures,  but  rather  planes  of  shattered  rock  like  fissures 
filled  with  rubble.  Deposit  in  such  a  water-way  forms  a  breccia  of 
country  rock,  cemented  with  vein-stuff.  Or,  again,  in  certain  country 
rocks  soluble  in  water,  especially  limestones,  the  rock  is  dissolved  along 
the  water-way,  and  the  vein-stuff  deposited  pari  passu,  giving  rise  to 
what  are  called  substitution-veins.  In  short,  once  conceive  clearly  that 
mineral  veins  are  filled  water-ways,  and  all  these  complex  phenomena 
solve  themselves.  Even  porous  rocks  like  sandstones,  because  of  their 
porosity,  become  the  depositaries  of  vein-stuff,  though  not  in  paying 
quantities,  except  along  lines  or  planes  where  water-transit  is  more 
easy  and  abundant.  Examples  of  such  deposits  are  found  in  the  silver- 
bearing  and  copper-bearing  sandstones  of  Utah  and  New  Mexico.* 

Thus  there  seems  no  longer  any  room  for  doubt  that  metalliferous 
veins  are  deposits  from  solutions  in  water-ways  of  any  kind,  but  mostly 
from  hot  alkaline  solutions  coming  up  through  great  fissures.  It  is 
only  the  exact  chemical  reaction  which  is  yet  obscure.  The  work  of 
the  geologist  is  all  but  complete ;  the  problem  must  now  be  turned  over 
to  the  chemist.  It  may  be  interesting,  however,  before  leaving  this 
subject,  to  consider  separately  the  auriferous  veins  of  California,  and 
apply  to  them  the  principles  set  forth  above. 

Auriferous  Veins  of  California. — Gold  is  one  of  the  most  insoluble 
of  substances,  and  the  occurrence  of  this  metal  in  veins  has  always 
been  regarded  as  a  difficulty  in  the  way  of  the  solution  theory.  The 
only  free  solvent  of  gold  is  a  solution  of  free  chlorine;  but  this  does 
not  exist  in  Nature.  Nevertheless,  gold  is  known  to  be  slightly  solu- 
ble in  the  salts,  especially  the  persalts  of  iron.  It  is  also  quite  soluble 
as  gold  sulphide  in  alkaline  sulphides.  It  is  probable,  therefore,  that 
the  usual  solvents  of  gold  are  iron  sulphates,  and  especially  alkaline  sul- 
phides. There  is  also  a  silicate  of  gold,  which,  according  to  Bischof,  is 
slightly  soluble  under  certain  conditions. 

There  is  abundant  evidence  that  the  auriferous  quartz-veins  of  Cali- 
fornia have  been  deposited  from  hot  solutions.  These  veins  exhibit  in 
many  cases  the  characteristic  ribbon-structure.  They  exhibit  also  the 
water-cavities  characteristic  of  deposits  from  solutions,  and  the  vacuous 
spaces,  indicating  that  the  solutions  were  hot.  By  actual  experiment,! 
the  temperatures  at  which  the  vacuous  spaces  disappear,  and  therefore 
at  which  the  deposit  took  place,  have  been  ascertained — being  180°, 

*  Cazin,  Newbeny,  etc.,  Report  on  Nacimiento  Copper-Mines  of  New  Mexico. 
f  Arthur  Phillips,  ibid. 


248  STRUCTURE  COMMON  TO  ALL  ROCKS. 


350°  P.,  and  even  more.  Again,  there  can  be  no  doubt  that 
the  associated  metallic  sulphides  were  deposited  from  the  same  solu- 
tions as  the  vein-stuffs,  for  they  are  completely  inclosed  in  the  latter. 
But  the  gold,  as  already  stated  (p.  240),  exists  as  minute  crystals  and 
threads  of  metal  inclosed  in  the  sulphide  of  iron^  and  must  therefore 
have  been  deposited  from  the  same  solution  as  the  iron.  It  seems 
possible  that  the  gold  was  dissolved  in  a  solution  of  sulphate  of  iron, 
and  that  the  sulphate  was  deoxidized,  and  became  insoluble  sulphide 
and  precipitated  ;  and  that  the  gold  thus  set  free  from  solution  was 
entangled  in  the  sulphide  at  the  moment  of  the  precipitation  of  the 
latter.  Or  else,  and  more  probably,  the  gold  was  dissolved  as  sulphide 
along  with  iron  sulphide  in  an  alkaline  sulphide  solution  and  deposited 
by  reactions  1  or  4  given  on  page  245,  the  gold,  on  account  of  its  feeble 
affinities,  giving  up  its  sulphur  at  the  moment  of  its  deposit.* 

There  are  some  phenomena  connected  with  the  occurrence  of  gold 
in  the  iron  sulphides  of  the  deep  placers  which  seem  to  prove  the  truth 
of  this  view.f  The  deep  placers  of  California  are  gravel-drifts  in  an- 
cient river-beds,  covered  up  by  lava-flows  100  to  200  feet  thick.  These 
placers  are  worked  by  running  tunnels  beneath  the  basaltic  lava  until 


N  S 

FIG.  218.— Section  across  Table  Mountain,  Tuolumne  County,  California:  L,  lava;  G,  gravel;  S,  S, 
slate;  £,  old  river-bed;  £',  present  river-bed. 

the  river-gravel  is  reached.  Now,  the  waters  percolating  through  these 
lava-flows  and  reaching  the  subjacent  gravels  are  charged  with  alkali 
from  the  lava.  These  alkaline  waters  are  also  charged  with  silica 
from  the  same  source.  Hence,  the  drift-ivood  of  these  ancient  rivers 
has  all  been  silicified  by  these  siliceous  waters.  The  gravels  are  also  in 
many  places  cemented  by  the  same  material.  These  percolating  waters 
have  evidently  also  contained  iron ;  for  in  contact  with  the  silicified 
wood  is  often  found  iron  sulphide.  There  are  two  ways,  in  either  of 
which  we  may  imagine  the  gold  to  have  been  deposited.  It  may  have 
been  in  solution  in  the  iron  sulphate ;  or  else,  along  with  the  iron  in 
alkaline  sulphide.  Following  out  the  process  on  the  first  supposition, 
while  the  wood  decayed  it  was  partly  replaced  by  silica  and  partly  by 
iron  sulphide  produced  by  deoxidation  of  the  sulphate  by  organic  mat- 
ter (p.  193).  The  gravel  has  also  in  some  places  been  cemented  by 

*  Gold  is  soluble  in  sodium  sulphide,  probably  as  gold  sulphide. — Becker. 
\  Arthur  Phillip?,  ibid. 


THEORY   OF   METALLIFEROUS  VEINS.  249 

iron  sulphide  reduced  from  solution  in  a  similar  way.  Now,  both  in 
this  petrifying  and  in  this  cementing  sulphide  of  iron  is  found  (by  so- 
lution in  nitric  acid)  gold :  sometimes  in  rounded  grains,  and  there- 
fore simply  inclosed  drift-gold  ;  but  also  sometimes  in  minute  crystals 
and  threads,  exactly  as  in  the  sulphide  of  the  undecomposed  quartz- 
vein.  Evidently,  this  gold  has  been  deposited  from  a  solution  of  sul- 
phate of  iron  at  the  moment  of  the  reduction  of  the  latter  to  a  sul- 
phide. The  process  was  probably  as  follows :  Percolating  water  oxi- 
dized iron  sulphide  and  took  it  into  solution  as  sulphate.  This  solu- 
tion coming  in  contact  with  drift-gold,  dissolved  it,  but,  subsequently, 
coming  in  contact  with  decaying  organic  matter,  was  again  deoxidized 
and  deposited  as  sulphide ;  and  the  gold  crystallizing  at  the  same  mo- 
ment is  inclosed.*  Or  following  out  the  process  on  the  second  suppo- 
sition, gold  sulphide  in  solution  in  alkaline  sulphide,  coming  in  contact 
with  decaying  wood,  would  be  deposited  by  neutralization  of  the  alkali 
along  with  other  metallic  sulphides  present  and  be  entangled  with  them. 
But,  on  account  of  its  feeble  affinities,  the  gold  would  give  up  its  sul- 
phur either  to  the  alkaline  sulphide  or  to  the  sulphide  of  iron  and  be 
deposited  in  a  metallic  form.  Now,  a  similar  reaction  would  take  place 
in  a  fissure,  and  form  a  gold-bearing  vein.  In  fact,  the  sub-lava  gravels 
may  be  regarded  as  a  horizontal  water-way  or  fissure  with  its  walls 
through  which  water  circulates  and  deposits. 

Suppose,  then,  we  have  hot  water  containing  alkaline  carbonate  and 
alkaline  sulphide,  holding  in  solution  silica  and  metallic  sulphides, 
among  them  gold  sulphide,  and  coming  upward  through  a  fissure.  By 
any  of  the  reactions  on  page  245,  e.  g.,  by  cooling,  silica  would  depositv 
as  quartz  vein-stuff  and  the  gold  would  deposit  with  other  metallic 
sulphides,  giving  up,  however,  its  sulphur  in  the  act  of  deposition,  as 
before  explained.  If  the  alkaline  waters  contained  no  other  metallic 
sulphide  but  gold  sulphide,  then  the  gold,  giving  up  its  sulphur  to  the 
alkaline  sulphide,  would  be  found  in  form  of  metallic  gold  inclosed  in 
the  quartz  vein-stuff. 

Illustrations  of  the  Law  of  Circulation. — We  have  said  that  the 
iron  sulphate  comes  from  oxidation  of  sulphide,  but  also  the  sulphide 
from  the  deoxidation  of  the  sulphate.  This  is  only  another  example 
of  a  perpetual  cycle  of  changes.  Again,  the  gold  in  the  veins  is  leached 
from  the  strata ;  the  strata  doubtless  received  it  from  the  sea,  for  small 
quantities  of  gold  have  been  detected  in  sea- water ;  but,  again,  doubt- 
less the  sea  received  it  from  the  rocks,  and  this  brings  us  to  another 
perpetual  cycle  of  Changes. 

But  in  the  midst  of  all  these  changes  there  has  evidently  been  an 
increasing  concentration  and  availability  of  gold  and  other  metals.  In 

*  Arthur  Phillips,  ibid. 


250  STRUCTURE  COMMON  TO  ALL  ROCKS. 

the  strata  the  quantity  is  so  small  as  to  be  undetectable ;  it  is  thence 
carried  and  concentrated  in  veins  in  a  more  available  form ;  it  is  next 
set  free  along  the  backs  of  these  veins  in  a  still  more  available  form ; 
it  is  last  carried  down  by  currents  along  with  other  materials,  neatly 
sorted,  and  deposited  in  placers  in  a  form  the  most  available  of  all. 

SECTION  3. — MOUNTAINS:  THEIR  ORIGIN  AND  STRUCTURE. 

Mountains  are  often  regarded  as  types  of  permanence.  We  speak  of 
the  everlasting  hills.  The  first  lesson  taught  by  geology  is  that  all 
things,  even  the  most  stable,  are  slowly  changing.  In  this  section  we 
treat  of  the  origin,  growth,  maturity,  decay,  and  death — in  a  word,  the 
whole  life-history  of  mountains. 

Mountains  are  the  glory  of  our  earth,  the  culminating  points  of 
its  scenic  grandeur  and  beauty.  But  few  recognize  the  fact  that  they 
are  so,  only  because  they  are  also  the  culminating  points,  the  theatres 
of  greatest  activity,  of  all  geological  agencies.  The  study  of  mountains 
is  therefore  of  absorbing  interest  not  only  to  the  poet  and  painter,  but 
also  and  especially  to  the  geologist,  because  it  furnishes  the  key  to 
many  of  the  obscurest  problems  of  dynamical  geology. 

But  we  are  met  at  the  very  threshold  of  the  subject  by  a  difficulty 
arising  from  the  loose  use  of  the  term  mountain.  This  term  is  used 
for  every  conspicuous  elevation  above  the  general  level  of  the  surround- 
ing country,  whatever  may  be  its  dimensions  or  its  mode  of  origin. 
Thus  we  apply  it  to  a  whole  system  of  ranges,  such  as  the  Rocky- 
Mountain  system,  or  the  Andes,  or  the  Himalayas ;  or  to  each  compo- 
nent range  of  such  a  system,  such  as  the  Sierra  or  the  Wahsatch ;  or  to 
each  prominent  peak  on  such  a  range,  as,  for  example,  Mount  Lyell, 
Mount  Dana,  or  Mount  Shasta.  It  is  necessary,  therefore,  first  of  all, 
that  we  should  define  what  we  are  going  to  discuss. 

Definitions  of  Terms. — A  Mountain- System  is  a  great  complex  of 
more  or  less  parallel  ranges  in  the  same  general  region,  but  born  at 
different  times  (polygenetic).  It  is  a  family  of  mountains.  In  the 
Rocky-Mountain  system,  or,  as  it  is  better  called,  the  North  American 
Cordilleras,  we  have  the  Colorado  range  (Front  range),  the  Wahsatch 
range,  the  Basin  ranges,  the  Sierra  range,  and  several  others.  Simi- 
larly the  Andes  and  Himalayas  consist  of  several  ranges. 

A  Mountain- Range  is  a  single  mountain-individual  produced  by 
one  birth-throe  (monogenetic),  although  both  the  origin  and  the  subse- 
quent growth  is  a  slow  process.  The  Sierra,  the  Wfhsatch,  the  Uinta, 
and  the  Colorado  Mountains  are  good  examples. 

A  Mountain- Ridge  is  a  subordinate  part  of  a  range,  produced  either 
by  separate  folds  made  at  the  same  time,  or  by  faulting,  or  by  erosion. 
The  Blue  Ridge,  the  Alleghany,  and  the  Cumberland  Mountains  are  ex- 


MOUNTAIN   ORIGIN.  251 

amples  in  the  Appalachian  range.  The  parallel  folds  of  the  Jura  range 
— seen  in  cross-section  in  Fig.  223 — are  probably  the  best  examples. 

On  mountain-ridges  there  are  always  prominent  points  which  are 
called  Peaks,  whether  formed  by  volcanic  ejections  like  Mount  Shasta 
or  Mount  Ranier,  or  by  erosion  like  Mount  Dana  or  Mount  Lyell. 

Mountain-systems  are  separated  by  great  interior  Continental  basins 
like  the  Mississippi-river  basin.  Ranges  are  separated  by  great  inte- 
rior valleys,  like  Sacramento  and  San  Joaquin  Valley,  separating  the 
Sierra  from  the  Coast  range.  Ridges  afe  separated  by  longitudinal 
mountain- valleys,  while  the  transverse  valleys  which  trench  the  flanks 
of  ranges  or  ridges  head  in  the  passes  which  separate  the  peaks. 

Such  is  the  simplest  idea  of  mountain  form,  partially  realized  in 
some  cases.  But,  to  an  observer  looking  down  from  a  high  peak,  a 
mountain- range  often  seems  to  be  made  up  of  an  inextricable  tangle  of 
ridges  running  and  peaks  standing  in  every  conceivable  direction. 

lN"ow,  a  scientific  discussion  of  mountains  is  really  a  discussion  of 
ranges  or  mountain  individuals.  For,  on  the  one  hand,  a  mountain- 
system  is  only  a  multiplication  of  such  individuals  belonging  to  the 
same  family,  and  therefore  adds  no  new  element  to  the  discussion ;  and, 
on  the  other,  mountain  ridges  and  peaks  belong,  mainly  at  least,  to  the 
category  of  mountain  sculpture,  not  of  mountain  formation,  and  there- 
fore are  discussed  later. 

Greater  Inequalities  of  the  Earth- Surf  ace. — The  inequalities  of  the 
earth-surface,  as  already  explained  (page  167),  are  of  two  general  kinds, 
the  greater  and  the  lesser.  The  latter  belong  to  sculpture,  and  will  be 
taken  up  later.  Of  the  former  there  are  two  orders  of  greatness,  viz., 
those  constituting  land-masses  and  oceanic  basins,  and  those  consti- 
tuting mountain-ranges  and  intervening  valleys.  We  have  already  dis- 
cussed the  former ;  we  now  take  up  the  latter. 

^Mountain  Origin. 

Leaving  aside  for  the  present  all  disputed  points,  it  is  now  univers- 
ally admitted  that  mountains  are  not  usually  pushed  up  by  a  vertical 
force  from  beneath,  as  once  supposed,  but  are  formed  wholly  by  lateral 
pressure.  The  earth's  crust  along  certain  lines  is  crushed  together  by 
lateral  or  horizontal  pressure  and  rises  into  a  mountain-range  along  the 
line  of  yielding,  and  to  a  height  proportionate  to  the  amount  of  mash- 
ing. But  the  yielding  is  not  by  rising  into  a  hollow  arch,  nor  into  such 
an  arch  filled  beneath  with  liquid  (for  in  neither  case  could  the  arch 
support  itself),  but  by  a  mashing  together  and  a  thickening  and 
crumpling  of  the  strata  and  an  upswelling  of  the  whole  mass  along  the 
line  of  greatest  yielding.  That  this  is  the  immediate  or  proximate 
cause  of  the  origin  or  elevation  of  mountains  is  plainly  shown  by  their 
structure.  As  to  the  ultimate  cause — i.  e.,  the  cause  of  the  enormous 


252 


STRUCTURE  COMMOX  TO  ALL  ROCKS. 


lateral  pressure — this  lies  still  in  the  field  of  discussion, 
cuss  it  briefly  in  its  proper  place. 


We  shall  dis- 


Mountain  Structure. 

A  mountain-range,  then,  may  be  regarded  as  a  mass  of  enormously 
thick  strata  crushed  together  laterally  and  swelled  up  along  the  line  of 
crushing.  We  have  said  that  this  mode  of  origin  is  revealed  in  its 
structure.  We  can  best  make  this  plain  by  an  experiment.  Suppose, 
then,  we  place,  one  atop  another,  several  layers  of  any  plastic  substance, 
such  as  wax,  so  as  to  make  together  a  prismatic  mass,  as  represented  in 
section  in  Fig.  219,  A,  and  the  whole  resting  on  a  smooth  oiled  slab  of 

glass  or  steel,  so  that 

'5 ...::.::;:  ==::;=:=:....  1^616  Sl^ll  bC  nO 

friction  or  adhesion. 
Suppose,  further, 
that  very  gentle  heat 
be  applied  beneath 
along  the  middle 


line,  so  as  to  soften 
slightly  this  part. 
Of  course,  such  soft- 
ening would  be 
greatest  at  the  bottom,  and  become  less  and  less  upward  ;  also  greatest 
along  the  middle  line,  and  become  less  and  less  outward.  This  is  rep- 
resented in  the  figure  by  the  shading  and  in  nature  by  the  metamor- 
phic  softening,  of  which  we  will  speak  later.  Suppose,  now,  we  place  a 
board  on  each  side  of  the  prismatic  mass,  and  press  gradually  together. 
All  the  layers  will  be  thickened  and  folded,  and  the  whole  mass  swelled 
up  along  the  central  line  into  something  like  Fig.  219,  B.  AVe  have  in 
miniature  both  the  structure  and  the  mode  of  formation  of  a  mountain- 
range.  In  a  similar  way,  but  on  a  larger  scale,  all  great  mountain-ranges 
seem  to  have  been  formed. 


FIG.  219. 


FIG.  220.— Ideal  Section  across  the  Uintah  Mountains  (after  Powell). 


MOUNTAIN   ORIGIN  AND   STRUCTURE. 


253 


There  would  be  in  the  experiment,  and  much  more  would  wc  expect 
in  Xature,  some  variety  in  the  result  depending  upon  the  softness  or 


FIG.  221. 

stiffness  of  the  strata.  This  it  is  that  gives  rise  to  different  types  of 
mountains.  Sometimes  the  whole  mass  rises  as  one  great  fold  (Fig.  220). 
We  have  an  example 
of  this  in  the  Uintah 
range,  only  that  the 
fold  has  broken  down 
on  one  side,  forming  a 
great  fault  (Fig.  221). 
Sometimes  and  of  tener 
there  are  produced 
several  open  folds  like 
great  earth- waves  (Fig. 
222).  This  is  the  case  in  the  Jura  (Fig.  223).  Sometimes,  and  often- 
est  of  all,  there  are  produced  many  closely  oppressed  folds,  as  in  the  ex- 
periment (Fig.  219,  B).  This  is  the  case  in  the  Coast  Range  of  Cali- 
fornia (Fig.  224),  or  in  the  Appalachian  (Fig.  225).  Sometimes  the 


FIG.  222.— Ideal  Section  of  Jura  if  unaffected  by  Erosion. 


FIG.  223.— Section  of  Jura  as  modified  by  Erosion. 

mashing  is  so  extreme  that  the  sides  are  driven  in  under  the  swol- 
len central  parts,  so  that  the  strata  are  often  reversed.  This  is  .the 
case  in  the  Alps  (Fig.  226). 


LV 


FIG.  224.— Section  of  Coast  Range,  showing  Plication  by  Horizontal  Pressure. 

Proof  of  Elevation  ly  Lateral  Pressure  alone :  1.  Folding. — It  is 
evident  that  foldings  such  as  those  represented  in  all  the  above  figures, 


1  C 

FIG.  225.— Generalized  and  Simplified  Section  of  the  Appalachian  Chain. 


254 


STRUCTURE   COMMON   TO   ALL   ROCKS. 


and  which  occur  in  nearly  all  mountains,  can  not  be  produced  except  by 
lateral  pressure,  and  are  therefore  proof  of  such  pressure.     But,  more- 


FIG.  226. — Section  of  a  portion  of  the  Alps. 

over,  it  can  be  shown  that,  when  we  take  into  consideration  the  im- 
mense thickness  of  mountain  strata  and  the  degree  of  folding,  lateral 
pressure  is  sufficient  to  account  for  the  whole  elevation,  without  calling 
in  the  aid  of  any  upward  pushing  from  beneath.  For  example,  the 
Coast  Range  of  California  (Fig.  224)  is  composed  of  at  least  five  anti- 
clines and  corresponding  synclines.*  If  its  folded  strata  were  spread  out 
horizontally  in  the  position  of  the  original  sediments,  they  would  un- 
doubtedly cover  double  the  space.  Now,  supposing  the  strata  here  are 
only  10,000  feet  thick — a  very  moderate  estimate — in  mashing  to  one 
half  the  extent,  they  would  be  thickened  to  20,000  feet,  which  would 
be  a  clear  elevation  of  10,000  feet  if  they  had  not  been  subsequently 
eroded.  According  to  Eeiievier,f  a  section  of  the  Alps  reveals  seven 
anticlines  and  corresponding  synclines,  and  some  of  these  are  complete 
over-folds  (Fig.  226).  We  are  safe  in  saying  that  Alpine  strata  have 
been  mashed  horizontally  into  one  third  their  original  extent.  Sup- 
posing these  were  originally  30,000  feet  thick  (they  were  really  much 
thicker),  this  would  make  a  clear  elevation  of  60,000  feet.  Of  course, 
most  of  this  has  been  cut  away  by  erosion.  In  the  Appalachian  range, 
according  to  Claypole,J;  the  foldings  are  so  extreme  that  in  one  place 
95  miles  of  original  extent  have  been  mashed  into  16  miles,  or  six  into 
one,  and  yet  the  Appalachian  strata  are  estimated  as  40,000  feet  thick. 
Cases  of  still  greater  doubling  of  strata  upon  themselves  occur.  In  the 
Highlands  of  Scotland  the  strata  by  lateral  thrust  first  rose  in  a  fold, 
then  were  pushed  forward  into  an  over-fold,  then  broken  and  slidden 
one  over  another  for  ten  miles.*  In  the  Canadian  Rocky  Mountains 
there  is  an  overthrust  of  seven  miles,  by  which  the  Cambrian  is  made 

*  American  Journal  of  Science,  vol.  ii,  p.  297,  1876. 
f  Archives  des  Sciences,  vol.  lix,  p.  5,  1877. 

t  American  Naturalist,  vol.  xix,  p.  257,  1885. 

*  Geike,  Nature,  vol.  xxix,  p.  31,  1884. 


MOUNTAIN   ORIGIN  AND   STRUCTURE,  255 

to  override  the  Cretaceous  (McConnell).  The  manner  in  which  this 
was  done  is  illustrated  on  a  previous  page  (Fig.  205).  Evidently,  then, 
the  whole  height  of  the  mountains  mentioned  above  is  due  to  lateral 
crushing  alone. 

2.  Slaty  Cleavage. — But  there  is  another  phenomenon  associated 
with  mountains  which  furnishes  additional  proof,  if  any  be  necessary, 
viz.,  slaty  cleavage.  This  is  not  so  universal  a  phenomenon  as  folding, 
because  the  materials  of  strata  are  not  always  suitable  for  developing 
this  structure ;  but  where  it  occurs  its  evidence  is  equally  convincing. 
We  have  already  seen  (p.  183)  that  this  structure  is  always  produced 
by  mashing  together  horizontally  and  extension  vertically.  We  have 
also  seen  that  in  every  case  of  well-developed  cleavage  the  whole  rock- 
mass  has  been  mashed  horizontally  three  parts  into  one,  and  swelled 
up  vertically  one  part  into  three.  Now,  again,  considering  the  thick- 
ness of  mountain  strata,  this  is  sufficient  to  account  for  the  highest 
mountains  in  the  world.  It  is  true  we  often  find  slaty  cleavage  where 
there  are  now  no  mountains.  In  such  cases  the  elevation  produced 
by  the  mashing  has  been  swept  away  by  erosion.  We  find  only  the 
bones  of  the  extinct  mountains. 

It  was  once  supposed  that  mountains  were  pushed  up  from  below 
by  a  vertically  acting  force.  Hence  came  the  word  upheaval  as  applied 
to  mountains.  The  word  is  still  used ;  and  there  is  no  objection  to  its 
use,  if  it  be  borne  in  mind  that,  in  mountains  of  the  structure  given 
above,  the  force  of  upheaval  is  not  vertical  but  lateral. 

Modifications  of  the  Simple  Ideal  given  above.— Thus  far,  in  order 
to  get  a  clear  idea  of  the  process  and  the  result,  we  have  described 
mountains  in  their  simplest  form,  and  as  similar  in  process  of  formation 
and  result  to  the  experiment  shown  in  Fig.  219.  But  in  fact  the 
final  result  in  Nature  is  complicated  in  many  ways.  Some  of  these  com- 


FIG,  227. — Uintah  Mountains — Upper  Part  restored,  showing  Fault;  Lower  Part  showing  the  Pres- 
ent Condition  as  produced  by  Erosion  (after  Powell). 

plications  are  shown  in  the  foregoing  figures  of  actual  mountains,  and 
have  been  anticipated  in  their  descriptions.  It  is  necessary  now  to  dis- 
cuss these  more  fully : 


256  STRUCTURE   COMMON   TO  ALL  ROCKS. 

1.  By  Fracture  and  Slipping. — It  is  obviously  impossible  that  such 
violent  foldings  of  the  strata  should  take  place  without  frequent  fract- 
ure and  slipping  of  the  broken  parts.     These  fractures  and  faults  were 
produced  at  the  time  of  origin,  or  else  during  the  growth  of  the  range. 
If  the  mountains  are  very  old,  erosion  has  long  since  cut  down  the 

inequalities  thus 
produced;  but  if 
the  mountains 
are  recent,  they 
may  still  form 
conspicuous  oro- 

FIG.  228.— Layers  of  Clay  folded  by  Lateral  Pressure  (after  Favre).  oranhip  fpfltnrps 

In  Fig.  227  the  lower  part  shows  the  Uintah  Mountains  as  they  are, 
and  the  upper  part  shows  the  same  as  they  would  be  if  the  eroded  strata 
were  restored.  In  more  complex  mountains  the  fracturing  and  fault- 
ing are  also  more  complex.  Fig.  228  shows  the  result  of  an  actual 
experimental  crushing  of  variously-colored  layers  of  clay. 

2.  By  MetamorpJiism. — We  have  said  that  mountain  strata  are  often 
of  enormous  thickness.     We  shall  give  abundant  proof  of  this  here- 
after.   But  we  have  also  seen  (p.  221  et  seq.)  that  the  accumulation  of 
sediments  to  great  thickness  will  produce  a  rise  of  the  isogeotherms — 
an  invasion  of  the  sediments  with  their  included  water  by  the  interior 
heat,  and  a  consequent  hydrothermal  softening  or  incomplete  hydro- 
thermal  fusion  of  the  lower  parts  of  such  accumulations.    Now  we  find 
that  mountain  strata  are  nearly  always  more  or  less  metamorphic  in 
their  lower  parts.     Thus  every  great  mountain-range  has  a  metamor- 
phic core.     This  is  represented  in  the  experimental  figure  (Fig.  219) 
by  the  shading. 

3.  By  Subsequent  Erosion. — The  modifications  thus  far  spoken  of 
were  produced  at  the  time  of  preparation  or  else  in  the  origin  and 
growth  of  the  mountain,  and  therefore  belong  to  the  category  of  mount- 
ain formation.     But  so  -soon  as  the  mountain  begins  to  rise,  it  begins 
to  be  sculptured  by  erosion  ;  and  when  we  remember  that,  on  account 
of  their  great  elevation  and  steep  slopes,  mountains  must  be  the  the- 
atres of  the  greatest  activity  of  erosion,  it  is  evident  that  the  meta- 
morphic core  will  often  be  exposed  by  erosion  along  the  crests.     Thus 
the  typical  structure  of  a  great  mountain-range  is  that  of  a   meta- 
morphic or  granitic  axis  emerging  along  the  crest  and  flanked   on 
each  side  by  strata  corresponding  to  one  another.     It  was  formerly 
supposed  that  the  granitic  axis  was  pushed  up  from  below,  breaking 
through  the  strata  and  appearing  above  them.      But  it  is  far  more 
probable  that  the  so-called  granitic  axis  is  only  the  metamorphic  core 
formed  as  already  explained,  and  exposed  by  subsequent  erosion.     Fig. 
229  is  an  ideal  of  a  mountain-range  on  this  view.     In  this  case  the 


MOUNTAIN   ORIGIN  AND   STRUCTURE. 


257 


FIG.  229.— Ideal  Section  of  a  Mountain-Range. 

core  is  only  metamorphic ;  and  remnants  of  unchanged  strata,  caught 
up  and  left  among  the  folds  of  the  crests,  show  that  these  strata  once 

extended  over  the  top,  and  that 
the  metamorphic  axis  is  exposed 
only  by  erosion.  Only  carry  the 
metamorphism  a  step  further  and 
the  erosion  a  little  deeper,  and  we 
FIG.  230.  have  the  granitic  axis  complete 

(Fig.  230). 

Mountains  are  made  out  of  Lines  of  Thick  Sediments.— But  the 
question  occurs,  "What  determines  the  place  of  a  mountain-range? 
The  answer  is,  A  mountain-range  while  in  preparation — before  it  be- 
came a  range — was  a  line  of  very  thick  sediments.  This  is  a  very  im- 
portant point  in  the  theory  of  mountain  origin,  and  therefore  must  be 
proved.  The  strata  of  all  mountains,  where  it  is  possible  to  measure 
them,  are  found  to  be  of  enormous  thickness.  The  strata  involved  in 
the  folded  structure  of  the  Appalachian,  according  to  Hall,  are  40,000 
feet  thick ;  the  strata  exposed  in  the  structure  of  the  Wahsatch,  ac- 
cording to  King,*  are  more  than  50,000  feet  thick ;  the  Cretaceous 
strata  of  the  Coast  Range,  according  to  Whitney,  f  are  20,000  feet  thick ; 
and  if  we  add  to  this  10,000  feet  for  the  Eocene  and  Miocene  strata, 
the  whole  thickness  is  probably  not  less  than  30,000  feet.  The  Alpine 
geologists  estimate  the  thickness  of  the  strata  involved  in  the  intricate 
structure  of  the  Alps  as  50,000  feet.  The  strata  of  Uintah,  according 
to  Powell,  are  32,000  feet  thick. 

Now,  it  must  not  be  imagined  that  these  numbers  merely  represent 
the  general  thickness  of  the  stratified  crust ;  only,  that  in  these  places 
the  strata  are  turned  up  and  their  edges  exposed  by  erosion,  and  thus 
their  thickness  revealed.  On  the  contrary,  it  may  be  shown  that  the 
same  strata  are  much  thinner  elsewhere.  The  same  strata  which  along 
the  Appalachian  range  are  40,000  feet  thick,  when  traced  westward  thin 
out  to  4,000  feet  at  the  Mississippi  River.  The  same  strata  which  along 
the  line  of  the  Wahsatch  are  30,000  feet  thick,  when  traced  eastward  thin 
out  to  2,000  feet  in  the  region  of  the  Plains.  J  It  is  evident,  therefore, 
that  mountain-ranges  are  lines  of  exceptionally  thick  strata. 

*  Fortieth  Parallel  Survey,  vol.  iii,  p.  451.  f  Whitney,  on  Mountain-Building. 

J  King,  Fortieth  Parallel  Survey,  vol.  i,  p.  122. 
17 


258  STRUCTURE   COMMON   TO  ALL  ROCKS. 

Mountain-Ranges  were  once  Marginal  Sea-Bottoms. — Where,  then, 
do  sediments  now  accumulate  in  greatest  thickness?  Evidently  on 
marginal  sea-bottoms,  off  the  coasts  of  continents.  The  greater  part 
of  the  washings  of  continents  are  deposited  within  30  miles  of  shore, 
and  the  whole  usually  within  100  miles.  From  this  line  of  thickest 
and  coarsest  deposit  the  sediments  grow  thinner  and  finer  as  we  go  sea- 
ward. But  evidently  such  enormous  thicknesses  as  40,000  feet  can  not 
accumulate  in  the  same  place  without  pari  passu  subsidence  such  as  we 
know  takes  place  now  whenever  exceptionally  abundant  sedimentation 
is  going  on  (p.  139).  Therefore,  mountain-ranges  before  they  were  yet 
born — while  still  in  preparation  as  embryos  in  the  womb  of  the  ocean 
— were  lines  of  thick  off-shore  deposits  gradually  subsiding,  and  thus 
ever  renewing  the  conditions  of  continuous  deposit. 

As  this  is  a  very  important  point,  it  is  necessary  to  stop  here  awhile 
in  order  to  show  that  such  was  actually  the  fact  in  the  case  of  all  the 
principal  ranges  of  the  American  Continent — i.  e.,  that  for  a  long  time 
before  they  were  actually  formed,  the  places  which  they  now  occupy 
were  marginal  sea-bottoms  receiving  abundant  sediments  from  an  ad- 
jacent continent.  We  shall  be  compelled  here  to  anticipate  some  things 
that  belong  to  Part  III,  but  we  hope  to  make  statements  so  general 
that  there  will  be  no  difficulty  in  understanding  them. 

1.  Appalachian. — The  history  of  this  range  is  briefly  as  follows : 
At  the  beginning  of  the  Palaeozoic  era  there  was  a  great  V-shaped 
land-mass,  occupying  the  region  now  covered  by  Labrador  and  Canada, 
then  turning  northwestward  from  Lake  Superior  and  extending  perhaps 
to  polar  regions  about  the  mouth  of  Mackenzie  River.  This  is  shown 
on  map,  Fig.  266,  on  page  292.  There  was  another  great  land-mass  oc- 
cupying the  present  place  of  the  eastern  slope  of  the  Blue  Ridge  and  ex- 
tending eastward  probably  far  beyond  the  present  limits  of  the  conti- 
nent— as  shown  in  the  same  figure  by  dotted  line  in  the  Atlantic  Ocean. 
The  western  coast-line  of  this  land-mass  was  the  present  place  of  the 
Blue  Ridge.  Westward  of  this  line  extended  a  great  ocean — "  the  in- 
terior Palaeozoic  Sea."  The  Appalachian  range  west  of  the  Blue  Ridge 
was  then  the  marginal  bottom  of  that  sea.  During  the  whole  of  the 
Cambrian,  Silurian,  and  Devonian,  this  shore-line  remained  nearly  in 
the  same  place,  although  there  was  probably  a  slow  transference  west- 
ward. Meanwhile,  throughout  this  immense  period  of  time,  the  wash- 
ings from  the  land-mass  eastward,  accumulated  along  the  shore-line,  until 
30,000  feet  of  thickness  was  attained.  At  the  end  of  the  Devonian  some 
considerable  changes  of  physical  geography  of  this  region  took  place, 
which  we  will  explain  when  we  come  to  treat  of  the  history  of  this  pe- 
riod. Suffice  it  to  say  now  that  during  the  Carboniferous  the  region  of 
the  Appalachian  was  sometimes  above  the  sea  as  a  coal-swamp,  and  some- 
times below,  but  all  the  time  receiving  sediment  until  9,000  or  10,000 


MOUNTAIN  ORIGIN   AND   STRUCTURE.  259 

feet  more  of  thickness  was  added,  and  the  aggregate  thickness  became 
40,000  feet.  Of  course,  it  is  impossible  that  such  thickness  could  ac- 
cumulate on  the  same  spot  without  pari  passu  subsidence  of  the  sea- 
floor.  In  fact,  we  have  abundant  evidence  of  comparatively  shallow 
water  at  every  step  of  the  process — evidence  sometimes  in  the  character 
of  the  fossils,  sometimes  in  the  form  of  shore-marks  of  all  kinds,  some- 
times in  the  form  of  searns  of  coal,  showing  even  swamp-land  condi- 
tions. Again,  of  course,  the  sediments  were  thickest  and  coarsest  near 
the  shore-line,  and  thinned  out  and  became  finer  toward  the  open  sea, 
i.  e.,  westward.  Finally,  after  40,000  feet  of  sediments  had  accumulated 
along  this  line  the  earth-crust  in  this  region  gave  way  to  the  lateral 
pressure,  and  the  sediments  were  mashed  together  and  folded  and 
swollen  up  into  the  Appalachian  range.  Subsequent  erosion  has 
sculptured  it  into  the  forms  of  scenic  beauty  which  we  find  there 
to-day. 

2.  Sierra. — This  was  apparently  the  first-born  of  the  Cordilleran 
family.      Its  history  is  as  follows :  During  the  whole  Palaeozoic  and 
earlier  part  of  the  Mesozoic,  there  was  in  the  Basin  region  a  land-mass, 
whose  form  and  dimensions  we  yet  imperfectly  know,  but  whose  Pacific 
shore-line  was  east  of  the  Sierra.     The  Sierra  region  was  therefore  at 
that  time  the  marginal  bottom  of  the  Pacific  Ocean.     Probably  the 
position  of  this  shore-line  changed   considerably  at  the   end  of  the 
Palaeozoic.      The  extent  of  this  change  we   will  discuss  hereafter. 
Suffice  it  to  say  now  that,  during  the  whole  of  this  time,  the  Sierra 
region  received  sediments  from  this  land-mass  until   an  enormous 
thickness  (how  much  we  do  not  know,  because  the  foldings  are  too 
complex  to  allow  of  estimate)  was  accumulated.     At  last,  at  the  end  of 
the  Jurassic,  the  sea-floor  gave  way  to  the  increasing  lateral  pressure 
along  the  line  of  thickest  sedinients,  and  these  latter  were  crushed  to- 
gether with  complex  foldings  and  swollen  up  into  the  Sierra.     An 
almost  inconceivable  subsequent  erosion  has  sculptured   it  into  the 
forms  of  beauty  and  grandeur  which  characterize  its  magnificent  scenery. 

3.  Coast  Range. — The  birth  of  the  Sierra  transferred  the  Pacific 
shore-line  westward,  and  the  waves  now  washed  against  the  western 
foot  of  that  range,  or  possibly  even  farther  westward  in  the  region  of 
the  Sacramento  and  San  Joaquin  plains.     At  this  time,  therefore,  the 
region  of  the  Coast  Range  was  the  marginal  bottom  of  the  Pacific  Ocean. 
During  the  whole  Cretaceous,  Eocene,  and  Miocene,  this  region  re- 
ceived abundant  sediments  from  the  now  greatly  enlarged  continental 
mass  to  the  eastward  ;  until  finally,  at  the  end  of  the  Miocene,  when 
30,000  feet  of  sediments  had  accumulated  along  this  line,  the  sea- floor 
yielded  to  the  lateral  pressure,  and  the  Coast  Range  was  born ;  and  the 
coast-line  transferred  to  near  its  present  position. 

4.  Wahsatch. — The  physical  geography  of  the  region  to  the  east  of 


260  STRUCTURE   COMMON   TO   ALL   ROCKS. 

the  Wahsatch  (Plateau  region)  during  Juro-Triaso  time,  is  little  known. 
But  during  the  Cretaceous  the  region  of  the  Wahsatch  was  the  western 
marginal  bottom  of  the  great  interior  Cretaceous  Sea  (see  map,  Fig! 
755,  p.  470),  receiving  abundant  sediments  from  the  great  land-mass  of 
the  Basin  and  Sierra  region.  This  greatly  increased  the  enormous 
thickness  of  sediments  already  accumulated  along  this  line  in  earlier 
times.  At  the  end  of  the  Cretaceous  the  sediments  yielded,  and  the 
Wahsatch  was  born.  It  is  necessary,  however,  to  say  that  both  the 
Sierra  and  Wahsatch  underwent  very  great  changes  of  form  produced 
by  a  different  process  and  at  a  much  later  period.  We  shall  speak  of 
this  later. 

5.  Alps. — Mr.  Judd  has  recently  shown  that  the  region  of  the 
Alps,  during  the  whole  Mesozoic  and  Early  Tertiary,  was  a  marginal 
sea-bottom,  receiving  sediments  until  a  thickness  was  attained  not  less 
than  that  of  the  Appalachian  strata.  At  the  end  of  the  Eocene  these 
enormously  thick  sediments  were  crushed  together  with  complicated 
foldings  and  swollen  upward  to  form  these  mountains  and  afterward 
sculptured  to  their  present  forms. 

The  same  may  be  said  of  the  Himalayas  and  nearly  all  other  mount- 
ains. We  may,  therefore,  confidently  generalize,  and  say  that  the  places 
now  occupied  by  mountain-ranges  have  been,  previous  to  their  forma- 
tion, places  of  great  sedimentation,  and  therefore  usually  marginal 
ocean-bottoms.  In  some  cases,  however,  the  deposits  in  interior  seas  or 
mediterraneans  have  yielded  in  a  similar  way,  giving  rise  to  more  ir- 
regular ranges  or  groups  of  mountains. 

It  is  easy  to  see  now  why  mountain-ranges  so  often  form  the  bor- 
ders of  continents,  and  that  continents  consist  essentially  of  interior 
basins  with  coast-chain  rims.  The  view  of  formation  of  mountains, 
above  presented,  necessitates  this  as  a  general  form,  while  it  prepares 
us  for  exceptions  in  case  of  mountains  formed  from  mediterranean 
sediments.  We  see  also  why  in  the  case  of  parallel  marginal  ranges  of 
the  same  system,  such  as  the  Sierra  and  Coast  Kanges,  these  should  be 
formed  successively  seaward. 

Why  Thick  Sediments  should  be  Lines  of  Yielding.— Admitting, 
then,  that  mountains  are  formed  by  the  squeezing  together  of  lines  of 
very  thick  sediments,  the  question  still  occurs,  Why  does  the  yielding 
take  place  along  these  lines  in  preference  to  any  others  ?  This  is  a  capi- 
tal point  in  the  theory  of  mountain  formation.  The  answer  is  as  fol- 
lows :  We  have  already  seen  (p.  222)  that  accumulation  of  sediments 
causes  the  isogeotherm  to  rise  and  the  interior  heat  of  the  earth  to 
"  invade  the  lower  portion  of  the  sediments  with  their  included  waters. 
Now  this  invasion  of  heat  in  its  turn  causes  hydrothermal  softening  or 
even  fusion,  not  only  of  the  sediments,  but  also  of  the  sea-floor  on 
which  they  rest.  Thus  a  line  of  thick  sediments  becomes  a  line  of 


MOUNTAIN   ORIGIN  AND   STRUCTURE.  261 

softening  and  therefore  a  line  of  weakness,  and  a  line  of  yielding  to 
the  lateral  pressure,  and  therefore  also  a  line  of  mashing  together  and 
folding  and  up-swelling — in  other  words,  a  mountain-range.  As  soon 
as  the  yielding  commences  we  have  an  additional  source  of  heat  in  the 
crushing  itself.  It  follows  from  this  that  there  is  or  was  beneath  every 
mountain  a  line  of  fused  or  semi-fused  matter.  This  we  will  call  the 
sub-mountain  liquid.  This  by  cooling  and  solidification  becomes  a 
metamorphic  or  granitic  core,  which  by  erosion  forms  the  metamorphic 
or  granitic  axis  and  crest  of  many  great  mountains. 

Brief  History  of  a  Mountain-Range.— The  preparation*  of  a  future 
mountain  commences  by  the  accumulation  of  enormous  thickness  of 
sediment  off  a  coast-line.  This  is  the  embryonic  condition  of  the 
range ;  it  is  still  within  the  womb  of  ocean.  Next,  the  line  of  sedi- 
ments yields  to  the  ever-increasing  lateral  thrust,  and  the  mountain  is 
born.  As  soon  as  it  appears,  there  begin  to  act  upon  it  two  opposite 
forces — one  upheaving,  the  other  cutting  away ;  the  one  interior,  the 
other  exterior — which  may  be  compared  to  the  opposite  processes  of 
supply  and  waste  in  the  animal  body.  So  long  as  the  supply  exceeds 
the  waste,  the  mountain  grows.  When  these  opposite  processes  are  in 
equilibrium,  the  mountain  is  mature.  When  the  waste  by  erosion  ex- 
ceeds the  supply  by  upheaval,  the  mountain  has  entered  upon  its  period 
of  decay.  Finally,  the  destructive  forces  triumph,  and  the  mountain 
is  swept  clean  away  by  erosion.  This  is  mountain-death.  We  find 
mountains  in  all  these  stages.  The  Sierra,  the  Wahsatch,  and  the  Coast 
Range,  are  probably  still  growing.  The  Appalachian  is  already  mature 
or  probably  entered  on  its  period  of  decay.  In  the  folded  structures 
of  the  enormously  thick  rocks  of  the  Archaean  region  of  Canada  we  un- 
doubtedly find  the  bones  of  extinct  mountains. 

Slowness  of  Mountain  Origin  and  Growth. — Although,  as  we  shall 
see  in  Part  III,  the  formation  of  mountains  of  ten  marks  the  boundaries 
of  geological  periods,  and  therefore,  in  a  geological  sense,  the  process 
is  comparatively  rapid,  yet  in  a  human  sense  it  is  always  extremely 
slow — so  slow  that  it  may  and  probably  is  going  on  now  under  our 
eyes,  without  attracting  our  attention. 

Age  of  Mountains, — The  date  of  mountain-birth  is  determined  by 
the  age  of  the  strata.  It  must  be  later  than  the  youngest  strata  which 
enter  into  the  folded  structure  of  the  mountain  or  are  tilted  on  its 
flanks.  Thus  we  say  that  the  Appalachian  was  born  at  the  end  of 
the  Coal  period,  because  all  the  Palaeozoic  strata,  including  the  coal, 
enter  into  the  composition  of  its  folded  structure,  but  later  strata  do 
not.  We  say  that  the  Sierra  was  formed  at  the  end  of  the  Jurassic,  be- 
cause these  are  the  youngest  strata  which  are  folded  and  tilted  on  its 
flanks.  Similarly,  the  Cretaceous,  the  Eocene,  and  the  Miocene,  are  all 
crumpled  up  in  the  Coast  Range,  but  the  Pliocene  are  not.  Therefore 


262  STRUCTURE   COMMON   TO   ALL   ROCKS. 

we  judge  that  this  range  was  formed  at  the  end  of  the  Miocene.  To 
illustrate :  in  Fig.  230  (p.  257)  it  is  evident  that  the  strata  a  were  first 

deposited  in  a  horizontal 
position,  then  tilted  and 
eroded,  and  b  were  de- 
posited  unconformably  on 
their  eroded  edges.  The 

age  of  this  mountain,  therefore,  is  younger  than  a  and  older  than  b. 
Sometimes  several  movements  of  lifting  are  revealed.  Thus  in  Fig. 
231,  the  strata  a  were  deposited  horizontally,  then  tilted  by  mountain 
formation  and  eroded,  and  b  deposited  horizontally  and  unconformably 
on  their  edges ;  then  by  a  second  movement  b  was  lifted  (and  of  course 
a  also  at  a  higher  angle  than  before),  and  c  was  deposited  uncon- 
formably on  b. 

Now,  by  examination  of  mountains  in  all  parts  of  the  world,  it  is 
found,  as  might  have  been  expected,  that  all  the  highest  mountains  are 
comparatively  young,  and  that  the  oldest  mountains  are  of  moderate 
altitude.  The  reason  is  obvious  :  young  mountains  are  in  the  vigor  of 
youth,  and  perhaps  still  growing,  while  the  oldest  mountains  are  in  the 
last  stages  af  decay.  The  oldest  of  our  American  mountains  are  the 
low  Laurentides;  they  are  almost  gone;  they  are  pre-Cambrian. 
Then  follow  the  higher  Appalachian ;  they  are  pre-Triassic.  Then 
the  still  higher  Sierra ;  they  are  pre-Cretaceous.  To  mention  some 
foreign  examples :  the  Alps  has  certainly  risen  10,000  and  the  Hima- 
laya 19,000  feet*  since  Eocene  times ;  for  so  high  Eocene  marine  strata 
have  been  found  on  their  slopes. 

Other  Phenomena  associated  with  Mountains. — The  essential  phe- 
nomena demonstrating  the  process  of  mountain  formation  are  the 
folded  structure,  the  slaty  cleavage,  the  thickness  of  the  strata,  and  the 
position  along  the  borders  of  continents.  But  there  are  other  phe- 
nomena associated  with  mountains,  which  are  well  explained  by  the  lat- 
eral-pressure theory,  and  therefore  confirm  the  theory. 

1.  Fissures,  Fissure- Erupt  ions,  and  Dikes. — The  strong  foldings 
of  mountain  strata  inevitably  produce  fractures.  Often  these  fractures 
extend  down  to  the  sub-mountain  liquid,  and  this  latter  is  squeezed 
out  by  the  enormous  lateral  pressure,  through  the  fissures  and  out- 
poured on  the  surface  as  great  lava-floods — such  as  the  great  lava-flood 
of  the  Northwest,  and  the  Deccan  lava-flood,  already  described  on  pages 
210  and  211.  The  outpourings  on  the  surface  may  be  entirely  carried 
away  by  erosion,  and  the  filled  fissures  through  which  they  came  may 
be  exposed  as  dikes ;  or  else  the  sub-mountain  liquid  may  have  been 
forced  into  fissures  which  did  not  reach  the  surface,  and  these  also 

*  American  Journal  of  Science,  vol.  xxxvii,  p.  413,  1889. 


MOUNTAIN  ORIGIN  AND  STRUCTURE.  263 

may  be  exposed  by  erosion  as  dikes.     Thus  lava-floods  are  associated 
with  neiver  strata,  and  dikes  with  all,  but  especially  the  older. 

2.  Volcanoes. — Great  lava-floods  come  up  through  fissures  and  flow 
off  as  sheets.    By  repeated  eruptions  successive  sheets  accumulate  until 
the  whole  mass  is  several  thousand  feet  thick.    The  lower  parts  of  such 
lava-masses  remain  incandescently  hot  almost  indefinitely.     Percolat- 
ing water  reaching  these  hot  interior  portions  develops  force  sufficient 
to  eject  fused  matter  and  form  volcanoes  parasitic  on  the  lava-floods ; 
or  else  water  may  reach  the  sub-mountain  liquid  through  the  fissures 
produced  by  foldings  and  thus  also  produce  volcanoes.    Thus  volcanoes 
also  are  associated  with  mountain-ranges. 

3.  Mineral  Veins. — If  the  fractures  do  not  penetrate  deep  enough 
to  reach  the  sub-mountain  liquid,  then  they  are  not  filled  at  the  time 
of  their  formation  with  liquid  lava,  but  slowly  afterward  by  deposit  of 
mineral  matter  from  percolating  waters  and  form  veins.     Thus  min- 
eral veins  are  especially  abundant  in  mountain-regions. 

4.  Faults  and  Earthquakes. — The  walls   of  great  fissures,  as  we 
have  already  seen,  never  remain  in  their  original  position,  but  always 
slip  one  on  the  other  and  thus  form  faults,  which,  in  case  of  foldings 
by  lateral  presssure,  will  usually  be  reverse.    Hence  faults  are  associated 
with  mountains.    The  slipping,  however,  will  not  take  place  all  at  once 
but  very  sloivly,  and  yet  not  uniformly,  but  more  or  less  paroxysmally. 
Each  paroxysm  will  produce  an  earthquake.     The  original  fracturing 
will  also  produce  an  earthquake.     Thus  earthquakes  are  associated 
with  mountains,  especially  if  the  mountains  are  still  growing. 

We  see  thus  the  truth  of  the  proposition  with  which  we  set  out,  that 
mountains  are  the  theatres  of  the  greatest  activity  of  all  geological 
agencies.  They  are  first  the  places  of  greatest  activity  of  aqueous 
agencies  in  the  form  of  sedimentation  in  preparation  for  the  future 
mountains ;  then  of  igneous  agencies  in  the  birth  and  growth  of  the 
actual  mountain;  and,  finally,  again  of  aqueous  erosive  agencies  in 
sculpturing  them  into  forms  of  beauty,  but  also  in  the  decay  and  at 
last  in  the  complete  destruction  of  former  mountains. 

Cause  of  Lateral  Pressure. — We  have  thus  proved  that  the  imme- 
diate cause  of  the  origin  and  the  growth  of  mountains  is  lateral  press- 
ure acting  on  thick  sediments  crushing  them  together  and  swelling 
them  up  along  the  line  of  greatest  thickness.  But  still  the  question 
remains,  What  is  the  ultimate  cause,  i.  e.,  the  cause  of  the  lateral  press- 
ure f  This,  as  we  have  already  said,  lies  still  in  the  'domain  of  doubt 
and  discussion,  but  the  view  which  seems  most  probable  may  be  briefly 
stated  as  follows : 

In  the  secular  cooling  of  the  earth  there  would  be  not  only  unequal 
radial  contraction,  giving  rise,  as  shown  on  page  168,  to  continents  and 
ocean-basins,  but  also  unequal  contraction  of  the  exterior  as  compared 


264  STRUCTURE  COMMON  TO  ALL  ROCKS. 

with  the  interior.  At  first,  and  for  a  long  time,  the  exterior  would  cool 
fastest ;  but  there  would  inevitably,  sooner  or  later,  come  a  time  when 
the  exterior,  receiving  heat  from  abroad  (sun  and  space),  as  well  as 
from  within,  would  assume  an  almost  constant  temperature,  while  the 
interior  would  still  continue  to  cool  and  contract.  Thus,  therefore, 
after  a  while  the  interior  nucleus  would  contract  faster  than  the  ex- 
terior shell.  It  would  do  so,  partly  because  it  would  cool  faster,  and 
partly  because  the  co-efficient  of  contraction  of  a  hot  body  is  greater 
than  that  of  a  cooler  body.  Now,  as  soon  as  this  condition  was  reached, 
the  exterior  shell,  following  down  the  shrinking  nucleus,  would  be 
thrust  upon  itself  by  a  lateral  or  horizontal  pressure  which  would  be 
simply  irresistible.  If  the  earth's  crust  were  a  hundred  times  more 
rigid  than  it  is  (30  times  as  rigid  as  steel,  500  to  1,000  times  as  rigid 
as  granite — Woodward,  Science,  vol.  xiv,  p.  167  1889),  it  must  yield. 
Mountain-ranges  are  the  lines  along  which  the  yielding  takes  place, 
and  this  yielding  takes  place  along  lines  of  thick  sediments  because 
these  are  lines  of  weakness. 

There  are  several  serious  objections  which  may  be  brought  against 
this  view :  1.  Calculations  seem  to  show  that  the  amount  of  crumpling 
and  folding  actually  found  in  mountains  is  many  times  greater  than 
could  be  produced  by  the  contraction  of  the  earth  by  cooling.  v  But  it 
may  be  answered  that  there  may  be  other  causes  of  contraction  besides 
cooling.  For  example,  loss  of  constituent  gases  and  vapors  from  the 
interior  of  the  earth,  through  volcanic  vents  and  fissures,  has  been  sug- 
gested by  0.  Fisher  (p.  100). 

2.  Again,  it  has  been  shown  by  Dutton  that  it  is  impossible  that  the 
effects  of  differential  contraction  should  be  concentrated  along  certain 
lines,  so  as  to  give  rise  to  mountain-ranges  without  a  shearing  of  the 
crust  upon  the  interior  portions,  which  is  inadmissible  if  the  earth  be 
solid.  Instead,  therefore,  of  conspicuous  mountain-ranges,  the  effects 
of  differential  contraction  would  be  distributed  all  over  the  surface, 
and  be  wholly  imperceptible.  But  in  answer  to  this  it  may  be  said 
that  there  is  no  difficulty  in  the  way  of  such  shearing,  and  therefore 
of  such  concentration  of  effects  along  certain  weakest  lines,  if  there  he 
a  sub-crust  liquid  layer,  either  universal  or  else  underlying  large  areas 
of  surface. 

Still  other  objections  have  been  raised,  but  these  are  so  recent  that 
they  have  not  yet  been  sufficiently  sifted  by  discussion  to  deserve  men- 
tion here.  The  origin  of  mountains  by  lateral  pressure  is  a  fact  be- 
yond dispute.  This  is  the  most  important  fact  for  the  geologist.  How 
the  lateral  pressure  is  produced  is  a  pure  physical  question  which  must 
be  left  to  the  physicists  to  settle  among  themselves. 

Another  Type  of  Mountains— Monoclinal  Mountains.— We  have 
thus  far  spoken  only  of  one  type  of  mountains — by  far  the  commonest 


MOUNTAIN   ORIGIN  AND   STRUCTURE.  265 

type — including  the  greatest  mountains,  and  long  supposed  the  only 
kind.  But  there  is  another  type  only  recently  brought  to  light  by  the 
United  States  Geological  Survey,  the  most  conspicuous  if  not  the  only 
examples  of  which  are  found  in  the  Basin  and  part  of  the  Plateau  re- 
gions. These  mountains  are  formed  in  an  entirely  different  way,  viz., 
by  the  tilting  or  else  the  bodily  uplifting  of  great  crust-blocks,  sepa- 
rated by  parallel  fissures..  Mountains  of  the  usual  type  may  be  called 
anticlinals  ;  for,  although  often  made  up  of  many  anticlines  and  syn- 
clines,  yet,  taken  as  a  whole,  they  may  be  regarded  as  a  grand  anticline 
(see  Fig.  229,  p.  257).  Mountains  of  this  second  type  are  called 
"  monoclinaU"  In  mountains  of  the  first  type  the  faults  are  usually 
reverse,  in  the  second  type  they  are  normal.  Normal  faults  are  ex- 
tremely common  everywhere,  but  they  are  rarely  great  enough  to  give 
rise  to  earth-features  which  deserve  the  name  of  mountains ;  but  in 
the  Basin  region — as  we  have  already  seen,  page  233 — their  scale  is  so 
enormous  and  their  formation  so  recent  that  they  give  rise  to  very 
conspicuous  orographic  features.  We  have  already,  under  faults  (p. 
233),  sufficiently  explained  the  mode  of  formation  of  the  Basin  ranges. 
We  now  wish  to  explain  how  the  Sierra  has  been  modified — in  fact, 
received  its  present  form  and  altitude — in  this  way. 

The  Sierra,  as  we  have  already  seen,  was  formed  by  crushing  and 
folding  of  thick  sediments  at  the  end  of  the  Jurassic.  It  is  probable 
that,  by  the  enormous  erosion  of  the  Cretaceous  and  Tertiary  periods, 
it  was  subsequently  cut  down  to  very  moderate  altitude.  At  the  end  of 
the  Tertiary  this  great  mountain-block — 300  miles  long  and  50  to  70 
miles  wide — was  heaved  up  on  its  eastern  side,  forming  there  a  normal 
fault,  with  a  displacement  of  probably  not  less  than  15,000  feet.*  The 
range  was  thus  greatly  elevated,  and  its  crest  transferred  to  its  extreme 
eastern  margin.  The  movement  was  attended  with  lava-flows,  which 
ran  down  the  western  slope,  filling  up  the  old  river-beds,  and  displacing 
the  rivers.  The  displaced  rivers  immediately  commenced  cutting  new 
beds  (Fig.  8,  p.  16,  and  Fig.  218,  p.  248).  That  this  event  took  place  at 
the  end  of  the  Tertiary  is  shown  by  the  fact  that  even  the  most  recent 
Tertiary  beds  were  covered  by  the  lava.  That  the  slope  and  therefore 
the  height  of  the  mountain  were  greatly  increased  at  that  time  is  shown 
by  the  fact  that  the  rivers,  seeking  their  base-level  (p.  21),  have  cut 
their  new  beds  2,000  feet  below  their  old  beds,  even  though  the  time  of 
cutting  was  very  much  less.  Evidently,  therefore,  the  present  form 
and  height  of  the  Sierra  date  from  the  end  of  the  Tertiary. 

Coincidently  with  this  last  great  modification  of  the  Sierra,  the 
Basin  ranges  were  also  formed  by  crust-block-tilting.  On  the  other 

*  The  fault-scarp  is  10,000  feet,  and 'the  summit  slates  are  deeply  buried  beneath 
Quaternary  deposits  at  its  foot. 


266  STRUCTURE  COMMON  TO  ALL  ROCKS. 

boundary  of  the  Basin  region,  the  Wahsatch  was  at  the  same  time  also 
heaved  up  on  its  western  side,  forming  there  one  of  the  greatest  faults 
known.  Therefore,  so  far  as  their  present  forms  are  concerned,  the 
Sierra  and  Wahsatch  may  be  said  to  belong  to  the  Basin  system.  It 
is  not  difficult  to  imagine  how  the  whole  system  may  have  been  formed. 
At  the  end  of  the  Tertiary  the  whole  Basin  region,  including  the  Sierra 
on  one  side  and  the  Wahsatch  on  the  other,  was  lifted  probably  by 
intumescent  lavas  into  an  arch,  and  by  tension  split  into  great  oblong 
crust-blocks.  The  arch  broke  down,  the  crust-blocks  readjusted  them- 
selves, as  explained  on  page  233,  to  form  the  Basin  ranges,  and  left 
the  abutments,  viz.,  the  Sierra  and  the  Wahsatch,  with  their  raw  faces 
looking  toward  one  another  across  the  intervening  Basin.  The  pro- 
cess and  result  are  shown  in  the  ideal  diagram  (Fig.  232).  It  must  not 
be  imagined,  however,  that  this  took  place  at  once  as  a  great  cataclysm, 
but  rather  that  it  took  place  very  slowly — the  lifting,  the  breaking 
down,  and  the  readjustment,  all  going  on  at  the  same  time. 


FIG.  232.— Diagram  showing  Probable  Origin  of  the  Basin  System. 

Thus,  then,  there  are  two  types  of  mountains  strongly  contrasted, 
mountains  of  the  one  type  are  formed  by  lateral  pressure  and  crushing, 
of  the  other  type  by  lateral  tension  and  stretching.  The  one  gives  rise 
mainly  to  reverse  faults,  the  other  always  to  normal  faults.  Mountains 
of  the  one  type  are  formed  by  upswelling  of  thick  sediments,  those  of 
the  other  type  by  irregular  readjustment  of  crust-"blocks.  Mountains 
of  the  one  type  are  horn  of  the  sea,  those  of  the  other  type  are  born  on 
the  land.  We  find  examples  of  the  one  type  in  nearly  all  the  greatest 
mountains  everywhere,  but  especially  in  the  Appalachian,  the  Alps,  and 
the  Coast  Eange.  The  best  examples,  perhaps  the  only  examples,  of 
the  other  type  are  the  Basin  ranges.  Some  mountains,  as  the  Sierra, 
the  Wahsatch,  and  certainly  some  of  the  Basin  ranges,  belong  to  both 
types.  In  their  origin,  they  have  been  formed  in  the  first  way,  but 
afterward  have  been  modified  by  the  second  way.  Thus  the  first  is  the 
fundamental  method,  and  the  second  only  a  modifying  process.* 

Mountain  Sculpture. 

As  soon  as  a  mountain-range  lifts  its  head  above  the  general  level 
of  sea  or  land,  it  is  immediately  attacked  by  erosion.  All  the  grand 

*  On  this  whole  subject  see  papers  by  the  writer,  American  Journal  of  Science,  vol. 
xix,  p.  176,  1880;  vol.  xxxii,  p.  167,  1866. 


MOUNTAIN  SCULPTURE. 


267 


and  beautiful  forms  of  mountain  scenery  are  due  to  erosive  sculpturing. 
The  amount  carried  away  is  always  enormously  great,  usually  many  times 
greater  than  what  remains.  In  Fig.  227  (p.  255)  we  have  in  the  upper 
part  the  Uintah  Mountain  with  its  strata  restored,  i.  e.,  as  it  would  be 
if  never  ravaged  by  erosion ;  in  the  lower  part  we  have  it  as  it  now  ex- 
ists. The  extreme  thickness  removed  is  about  25,000  feet,  while  only 
about  8,000  feet  remain,  for  the  highest  peaks  are  now  only  10,000  to 
12,000  feet  high.  In  the  Appalachian — an  older  mountain — probably 
a  much  larger  proportion  has  been  carried  away.  The  amount  in  all 
cases  is  so  great  as  to  obscure  the  origin  of  mountains  arid  to  confuse 
the  use  of  the  term  mountain.  Hence  some  have  divided  mountains  into 
two  kinds,  viz.,  mountains  of  upheaval  and  mountains  of  erosion,  and 
some  have  even  gone  so  far  as  to  say  that  mountains  are  mere  remnants 
of  denuded  continents — the  prominent  points  of  a  differential  erosion. 
But  it  is  best  to  keep  distinct  in  the  mind  mountain  formation  and 
mountain  sculpture.  They  are  both  equally  important  in  the  final 
result.  If  igneous  forces  do  the  rough  hewing,  aqueous  forces  do  the 
shaping  into  forms  of  beauty.  When  we  view  mountains  from  a  dis- 
tance, the  blue,  cloud-like  bank  which  we  see  on  the  horizon  is  the 
result  of  igneous  agencies ;  but,  when  we  are  among  mountains,  all  that 
we  see — every  ridge  and  peak  and  valley — all  that  constitutes  scenery — 
is  the  result  of  aqueous  agencies. 

Sculptural  Forms. — The  mode  of  mountain  formation  is  more  or 
less  concealed  in  internal  structure ;  but  the  forms  developed  by  sculpt- 
ure lie  on  the  surface,  and  are  easily  understood,  and  yet  they  often 
reveal  structure  to  the  careful  observer.  A  knowledge  of  these  sculpt- 
ural forms  gives'  additional  charm  to  mountain  travel.  They  are  al- 
most infinitely  diversified ;  yet  a  few  of  the  most  common  and  con- 
spicuous may  be  given  as  examples.  These  forms  are  not  all  confined 
to  mountains ;  some  of  them  are  the  general  forms  of  highland  erosion  •, 
but  they  are  most  conspicuous  in  mountain-regions. 


FIG.  233. 

1.  Horizontal  Strata. — (a.)  These,  if  sufficiently  firm,  give  rise  to 
table-forms,  the  top  of  the  table  being  determined  by  a  slab  of  hard 


c  . 


LM 


FIG.  234.— Section  across  Cumberland  Plateau  and  Lookout  Mountain,  Tennessee. 


268 


STRUCTURE  COMMON  TO  ALL  ROCKS. 


stratum,  such  as  sandstone  or  grit,  or  by  a  lava-flow.  In  the  latter  case, 
the  horizontal  lava-blanket  gives  rise  to  tables,  whatever  be  the  position 
of  the  underlying  strata.  Good  examples  of  this  form  are  found  in  Illinois 
(Fig.  233),  in  Tennessee  (Fig.  234),  in  the  mesas  of  the  Plateau  region 
(Fig.  10,  p.  17),  and  in  Table  Mountain,  of  California  (Fig.  235). 


N  S 

FIG.  235. — Section  across  Table  Mountain,  Tnolumne  County,  California:  L,  lava;  G,  gravel;  S  S, 
slate;  R,  old  river-bed;  E't  present  river-bed. 

(#.)  But  if  the  horizontal  strata  are  soft,  inters tratified  sands  and 
clays,  their  erosion  gives  rise  to  fantastic  castellated  forms  of  peaks, 
turrets,  etc.,  such  as  are  found  in  the  Bad  Lands  of  the  Plains  and 
Plateau  region,  which  are  the  almost  unlithified  deposits  of  the  Terti- 
ary lakes  (Fig.  236). 


FIG.  236.— Mauvaises  Terres,  Bad  Lands  (after  Hayden). 

2.   Gently -undulating  Strata. — These  give  rise  to  synclinal  ridges 
and  anticlinal  valleys.     This  is  well  shown  in  diagram  (Fig.  237)  and 


FIG.  237.— Diagram  showing  Synclinal  Kidges  and  Anticlinal  Valleys  (after  NOe  and  De  Margerie). 


MOUNTAIN   SCULPTURE. 


269 


in  the  subjoined  section  of  the  Appalachian  coal-field  in  Pennsylvania 
(Fig.  238).     This  is  usually  explained  by  supposing  that  the  backs  of 


FIG.  238.— Section  of  Coal-Field  of  Pennsylvania  (after  Lesley). 

the  anticlinals  have  been  broken  or  loosened  by  tension  in  bending ; 
while  the  synclinals  have  been  hardened  by  lateral  pressure — and  there- 
fore the  anticlinals  have  yielded  more  easily  to  erosion.  But  Prof. 
Davis  has  shown  *  that  such  a  supposition  is  at  least  not  necesstiry. 
For  example :  if  we  have  a  series  of  undulating  strata,  some  hard 
and  some  soft  (Fig.  239),  the  erosion  will  be  most  rapid  on  the  anti- 


Fio.  239.— Ideal  Diagram  showing  how,  according  to  Davis,  Synclinal  Ridges  are  formed:  full 
lines,  actual  surfaces  and  structure;  dotted  lines,  original  surfaces  and  structure;  broken  lines, 
former  erosion-surfaces. 

clines  and  the  hard  stratum  (a)  will  be  reached  and  cut  through  first 
there.  As  soon  as  the  soft  stratum  beneath  is  reached  the  erosion  will  be 
still  more  rapid,  and  valleys  will  be  formed.  This  will  be  understood 
by  careful  inspection  of  the  figure. 

3.  Strongly-folded  or  Highly -inclined  Outcropping  Strata. — These 
give  rise  to  sharp  ridges  and  valleys,  the  ridges  being  determined  by 


FIG.  240.— Ideal  Section  across  an  Eroded  Fold,  consisting  of  Alternating  Soft  and  Hard  Strata 
(after  NOe  and  De  Margerie). 

the  outcrop  of  a  hard  stratum.  Fig.  240  is  an  ideal  diagram,  showing 
how  such  ridges  are  formed  by  erosion.  In  the  Rocky  Mountains,  where 
they  are  finely  shown  on  the  flanks  of  the  mountains,  they  are  called 
"  hog-backs."  Fig.  241  represents  this  form  of  sculpture  as  it  often 
appears.  It  is  seen  that  every  ridge  is  formed  by  outcrop  of  a  hard 
sandstone,  which  has  resisted  erosion  more  than  the  intervening  strata. 
Beautiful  examples  of  this  form  are  seen  in  parts  of  the  Appalachian. 


*  Science,  vol.  xii,  p.  320. 


270 


STRUCTURE   COMMON   TO   ALL   ROCKS. 


Standing  on  the  top  of  Warm  Springs  Mountain,  Virginia,  ten  or  twelve 
parallel  ridges  may  be  counted,  each  with  long  slopes  on  one  side  and 
steep  slopes  on  the  other,  like  billows  ready  to  break.  The  crest  of 
each  ridge  is  determined  by  the  outcrop  of  a  hard  sandstone.  Such 
ridges  may  be  formed  either  by  the  outcrop  of  successive  sandstones, 


5  Sh  S  <fh  S  #K  & 

FIG.  241.— Parallel  Ridges. 

as  in  Fig.  241,  or  else  by  the  successive  outcrop  of  the  same  sandstone, 
as  in  Fig.  242. 

In  ridges  formed  in  this  way  the  relative  angle  of  slope  on  the  two 
sides  of  the  ridges  will  depend  on  the  dip  of  the  strata.     If  the  strata 


FIG.  242.— Parallel  Ridges  in  Folded  Strata. 

be  vertical,  the  two  slopes  will  be  equal.  If  the  strata  are  inclined,  the 
longer  slope  will  be  on  the  side  toward  which  the  strata  dip ;  and  the 
difference  of  the  two  slopes  will  increase  as  the  angle  of  dip  becomes 
less.  This  is  shown  in  Fig.  243  (a,  I,  and  c).  Finally,  one  slope  may 


FIG.  243. 

coincide  with  the  face  of  the  hard  stratum,  as  in  Fig.  240.     This  case, 
therefore,  passes  by  insensible  gradations  into  the  next,  viz. : 

4.  Gently -inclined,  almost  Level  Strata. — These,  by  erosion,  per- 
haps under  peculiar  climatic  conditions,  give  rise  to  a  succession  of 
broad,  nearly  level  tables,  coincident  with  the  face  of  a  hard  stratum, 
terminated  each  by  a  vertical  or  nearly  vertical  cliff.  This  form  of 
sculpture  is  developed  on  a  magnificent  scale  in  the  Colorado  plateau 
region.  Fig.  244  is  a  bird's-eye  view  of  three  such  tables,  each  20  to  60 
miles  wide,  and  terminated  by  cliffs  1,500  to  2,000  feet  high.  Fig.  245 
is  an  ideal  section  of  such  tables  and  cliffs — the  dotted  lines  showing  the 


MOUNTAIN   SCULPTURE. 


271 


portion  carried  away  by  erosion.     It  is  evident  that  the  drainage  of 
each  table  is  against  the  cliff ;  and  every  cliff,  therefore,  recedes  partly 


FIG.  244.— Bird's-eye  View  of  the  Terrace  Caflon  (after  Powell). 

by  under-cutting  by  a  river  and  partly  by  rain-wash  on  its  face.     In 
some  cases,  where  the  lifting  of  the  strata  was  dome-like,  the  receding 


2T2 


STRUCTURE  COMMON  TO  ALL  ROCKS. 


cliffs  are  circular,  producing  thus  titanic  amphitheatres,  100  or  more 
miles  across,  with  cliff-benches  1,000  to  2,000  feet  high.*  How  slo,w  the 
lifting  of  the  strata  in  this  region  must  have  been  is  shown  by  the  fact 

that  the  Green 
Elver  runs  against 
the  slope  of  the 
strata,  cutting  its 


FIG.  245. — Dotted  lines  show  material  carried  away  by  erosion. 


canon  deeper  to 
the  edge  of  the 
cliffs,  as  shown  in 
Fig.  244.  Evidently  the  strata  were  lifted  athwart  the  course  of  the 
river,  but  so  slowly  that  the  river  cut  as  fast  as  the  strata  lifted. 

Migration  of  Divides. — If  the  slopes  on  the  two  sides  of  a  divide 
are  equal,  the  position  of  the  divide  remains  stationary ;  but  if  one 
slope  be  steeper  than  the  other,  then  by  the  greater  erosion  on  the 
steeper  slope  the  divide  will  move  steadily  toward  the  gentler  slope. 
Thus,  the  rivers  on  the  steeper  slope  continually  increase  their  drainage 
areas  by  appropriating  from  the  other  side.  Examples  of  this  may  be 
found  in  nearly  all  mountains,  but  especially  in  those  of  the  monoclinal 
type,  and  in  all  ridges,  but  especially  in  the  case  of  hog-backs  (Figs. 
240, 241).  The  recession  of  plateau  cliffs  is  only  an  extreme  case  under 
this  law. 

5.  Metamorphic  and  Granitic  Rocks. — Sculptural  forms  in  these 
are  usually  irregular,  and  can  not  be  reduced  to  a  simple  law.     But,  in 
some  cases,  peculiar  forms  are  traceable  to  peculiar  structure.     Thus, 
for  example :  in  and  about  the  Yosemite  Valley  two  kinds  of  forms  are 
found,  viz.,  (a)  perpendicular  cliffs  and  towers  and  spires  of  the  valley 
itself ;  and  ( V)  rounded  domes  abundant  in  the  high  region  about  the 
valley.     The  one  is  the  result  of  a  rough,  imperfect  vertical  cleavage  of 
the  rock ;  the  other  of  a  concentric  structure  on  a  huge  scale,  usually 
undetectable  in  the  sound  rock, 

but  brought  out  by  weathering. 
This  is  shown  in  the  diagram 
(Fig.  246). 

6.  The  Kind  of  Agent.— It 
is  probable  that  the  nature  of 
the  erosive  agent,  whether  as 

rain  and  rivers  or  as  snow  and  glaciers,  also  determines  peculiar  scen- 
ic forms.  It  is  probable  that  the  former  tend  more  to  rounded  sum- 
mits and  ridges  and  V-shaped  gorges,  the  latter  to  sharp  summits 
(aiguilles)  and  comb-like  divides  and  broad  U-shaped  valleys. 


FIG.  246.— Ideal  Section  showing  Dome-structure. 
Dotted  line  above  shows  original  surface. 


*  Dutton— High  Plateaus  of  Utah,  p.  19. 


DENUDATION,  OR  GENERAL  EROSION.  273 

CHAPTER  VI. 
DENUDATION,   OR   GENERAL  EROSION. 

As  a  fit  ending  of  Part  II,  and  preparation  for  Part  III,  in  which 
the  idea  of  time  is  the  underlying  element,  it  seems  appropriate  to 
make  some  rough  estimate  of  the  amount  of  general  erosion  which  has 
taken  place  in  the  history  of  the  earth,  and  of  geological  time  based 
thereon. 

The  term  denudation  is  used  by  geologists  to  express  the  general 
erosion  which  the  earth-surface  has  suffered  in  geological  times.  The 
correlative  of  denudation  is  sedimentation,  and  the  amount  of  denuda- 
tion is  measured  by  the  amount  of  stratified  rocks. 

Agents  of  Denudation. — The  agents  of  erosion,  as  we  have  already 
seen  in  Part  I,  are :  1.  Rivers,  including  under  this  head  the  whole 
course  of  rainfall  on  its  way  back  to  the.  ocean  whence  it  came ;  2. 
Glaciers,  including  under  this  head  not  only  glaciers  proper,  but  moving 
ice-sheets,  such  as  now  exist  in  polar  regions,  and  in  the  Glacial  epoch 
extended  far  into  now  temperate  regions,  and  also  moving  snow-fields, 
for  it  is  probable  that  all  extensive  snow-fields  and  snow-caps  are  in 
motion ;  3.  Waves  and  tides  ;  and,  possibly,  4.  Oceanic  currents. 

Oceanic  currents  usually  run  on  a  bed  and  between  banks  of  still 
water,  and  therefore  produce  no  erosion.  It  is  possible,  however,  that 
a  rising  sea-bottom  may  be  eroded  by  this  agent ;  but  as  we  have  no 
knowledge  of  such  effects,  we  are  compelled  to  omit  this  from  our  esti- 
mate of  the  probable  rate  of  denudation.  The  action  of  waves  and  tides 
is  violent  and  conspicuous ;  yet  these  agents  are  so  entirely  confined  to 
the  shore-line  that  their  aggregate  effect  is  but  a  small  fraction  of  the 
whole  erosion.  Prof.  Phillips  has  shown  *  that,  taking  the  coast-lines 
of  the  world  as  100,000  miles,  and  making  the  extravagant  estimate 
that  the  average  erosion  along  this  whole  line  is  equal  to  that  of  the 
English  coast,  or  one  foot  per  annum  of  a  cliff  one  hundred  feet  high, 
still  the  aggregate  wave-erosion  is  far  less  than  river-erosion,  being 
equivalent  to  a  general  land-surface  erosion  of  only  2  0*0"0  of  an  inch 
per  annum,  or  -^  of  that  which  is  now  going  on  over  the  hydrographi- 
cal  basin  of  the  Ganges,  and  \  of  that  going  on  in  the  basin  of  the 
Mississippi.  Glaciers  and  rivers,  therefore,  are  the  great  agents  of  ero- 
sion. The  one  takes  the  place  of  the  other,  according  as  falling  water 
takes  the  form  of  rain  or  snow  ;  both  come  under  the  general  head  of 
circulating  meteoric  water.  In  a  general  estimate  of  the  rate  of  denu- 
dation we  may,  therefore,  without  sensible  error,  regard  it  as  the  work 
of  circulating  meteoric  water. 

*  Life,  its  Origin,  and  Succession,  p.  130. 
18 


274 


DENUDATION,  OR  GENERAL  EROSION. 


Again,  although  it  is  probable  that  the  erosive  power  of  glaciers  is 
greater  than  that  of  rivers,  yet  their  action  is  so  much  more  local,  both 
in  time  and  space,  that  we  believe  we  may  take  the  average  rate  of 
river-erosion  as  a  fair  representative  of  the  average  rate  of  denudation. 
Amount  of  Denudation. — A  mere  glance  at  the  figures  below  will 
show  in  a  general  way  the  manner  in  which  geologists  estimate  the 
amount  of  denudation  in  certain  regions.  In  almost  all  countries, 
especially  in  mountain-regions,  we  find  slips  varying  from  a  few  feet 
(Fig.  247)  to  many  thousands  of  feet  perpendicular  (Fig.  227).  There 

are  slips  in  the  Appalachian  chain  which  are 
estimated  to  be  8,000  and  even  one  20,000 
feet,  in  the  Uintah  20,000,  in  the  Wahsatch 
40,000  feet,  perpendicular.  And  yet  in 
most  cases  the  escarpment,  which  would 
otherwise  exist,  is  completely  cut  away,  so 
that  no  surface-indication  of  the  slip  exists. 
Evidently  in  such  cases  there  must  have 
been  erosion  on  the  elevated  side,  at  least  equal  to  the  amount  of  slip, 
and  probably  much  greater.  The  dotted  line  represents  the  probable 
original  surface. 

Sometimes  the  horizontal  strata  of  isolated  mountain-peaks  corre- 
sponding to  each  other  (mountains  of  erosion)  show  that  these  are  but 


«  FIG.  241 


FIG.  248.— Denudation  of  Red  Sandstone,  Northwest  Coast  of  Ross-shire,  Scotland. 


scattered  fragments  of  a  once  high  plateau,  which  has  been  removed  by 
erosion,  as  shown  in  the  annexed  figure  (Fig.  248)  and  in  many  of  the 


FIG.  249.— Section  across  Middle  Tennessee.    The  dotted  lines  show  the  amount  of  matter  removed. 

figures  on  pages  269  and  270.     In  such  cases  the  erosion  must  have 
been  at  least  equal  to  the  height  of  the  peaks,  and  may  have  been  to 


FIG.  250.— Section  through  Portions  of  England. 


DENUDATION,   OR   GENERAL   EROSION. 


275 


any  extent  greater.  The  accompanying  section  across  Middle  Tennes- 
see shows  a  vertical  erosion  of  1,200  to  2,400  feet,  over  the  whole 
valley  of  Middle  Tennessee,  which  is  sixty  miles  across  and  one  hun- 
dred miles  long.  In  most  cases  the  removed  matter  is  not  so  easily 
estimated  as  in  those  mentioned.  The  strata  in  mountain-chains  are 


FIG.  251.— Section  through  Portions  of  England. 

usually  folded  in  a  very  complex  way,  and  then  denuded.  But  the 
ideal  restoration  of  these  may  be  effected,  and  the  amount  of  erosion 
approximately  estimated.  Figs.  250  and  251  are  sections  across  the 
mountainous  parts  of  England,  as  restored  by  Prof.  Ramsay. 

Average  Erosion. — By  these  methods  Prof.  Ramsay  estimates  the 
denudations  over  many  portions  of  England  to  be  not  less  than  10,000 
to  11,000  feet  in  thickness.*  Over  the  whole  Appalachian  region  the 
denudation  has  probably  been  enormous,  in  some  places  8,000  to  20,000 
feet.  Over  the  whole  region  of  the  high  Sierra  Range,  as  we  have 
shown, f  erosion  has  removed  the  whole  of  the  Jurassic  and  Triassic 
slates,  and  bitten  deep  into  the  underlying  granite.  The  thickness  of 
these  slates  is  not  known,  but  it  must  be  many  thousand  feet.  In  the 
Uintah  Mountain  region,  according  to  Powell,  over  an  area  of  2,000 
square  miles,  an  average  thickness  of  three  and  a  half  miles  has  been 


FIG.  252. — Uintah  Mountains — Upper  Part  restored,  showing  Fault ;  Lower  Part  showing  the 
Present  Condition  as  produced  by  Erosion  (after  Powell). 

taken  away  (Fig.  252),  the  extreme  thickness  removed  being  nearly 
five  miles.     From  the  Wahsatch  have  been  removed  32,000  feet,  or 

*  Geological  Observer,  p.  819. 

f  American  Journal  of  Science  and  Arts,  vol.  v,  p.  825. 


276  DENUDATION,  OR  GENERAL  EROSION. 

six  miles  thickness  of  strata  (King).  Over  the  whole  Colorado  Plateau 
region  the  succession  of  cliffs,  separated  by  broad  tables  (Fig.  245), 
shows  enormous  erosion.  The  average  erosion  over  the  whole  region 
has  been  estimated  by  Powell  and  Dutton  as  6,500  feet ;  and  the  ex- 
treme general  erosion,  not  including  the  canon-cutting,  as  11,000  feet. 
The  whole  of  this  immense  mass  has  been  removed,  too,  since  the  mid- 
dle Tertiary. 

It  seems  impossible  to  avoid  the  conclusion,  therefore,  that  the 
average  erosion  over  all  present  land-surfaces  has  been  at  least  several 
thousand  feet. 

There  is  another  mode  of  estimating  the  average  erosion,  viz.,  by 
the  average  thickness  of  stratified  rocks.  The  debris  of  erosion  is  car- 
ried down  into  seas  and  lakes,  and  forms  strata,  and  the  amount  of 
stratified  rocks  becomes  'thus  the  measure  of  the  erosion ;  the  average 
thickness  of  sediments,  if  they  had  been  spread  over  an  equal  area, 
would  be  an  accurate  measure  of  the  average  thickness  removed  by 
erosion.  Now,  the  stratified  rocks  are  in  some  localities  10,000  feet, 
20,000  feet,  and  sometimes  40,000  and  50,000  feet  thick.  They  are 
scarcely  ever  found  less  than  2,000  or  3,000  feet.  It  is  certain,  there- 
fore, that  the  average  thickness  of  strata  over  the  whole  known  surface 
of  the  earth  is  not  less  than  several  thousand,  feet.  Let  us  take  it  at 
only  2,000  feet.  But  the  area  of  sedimentation,  the  sea-bottom,  is  now, 
and  has  probably  always  been,  at  least  three  times  the  area  of  erosion, 
the  land-surface.  Thus  an  average  of  2,000  feet  of  strata  would  require 
an  average  erosion  of  6,000  feet. 

Estimate  of  Geological  Times. — There  are  many  facts  connected 
with  geology,  especially  the  facts  of  evolution,  which  can  not  be  under- 
stood without  the  admission  of  inconceivable  lapse  of  time.  For  this 
reason  it  is  important  that  the  mind  should  become  familiarized  with 
this  idea.  It  will  not  be  out  of  place,  therefore,  to  make  a  rough  esti- 
mate of  time  based  upon  the  amount  of  erosion. 

We  have  already  seen  (p.  11)  that,  taking  the  Mississippi  as  an  aver- 
age river  in  erosive  power  (it  is  probably  much  more  than  an  average), 
the  rate  of  continental  erosion  is  now  about  one  foot  in  5,000  years.  At 
this  rate,  to  remove  an  average  thickness  of  6,000  feet  would  require 
30,000,000  years.* 

*  The  above  estimate  takes  the  average  thickness  of  strata,  and  supposes  it  spread 
evenly  over  the  whole  sea-bottom.  This  is  strictly  admissible  only  if  we  suppose,  with 
Lyell,  that  land  and  ocean  have  often  changed  places,  so  that  every  portion  of  earth-sur- 
face has  received  sediments.  But  if,  as  is  now  most  generally  believed,  the  ocean-basins 
have  remained  substantially  unchanged,  and  sediments  have  accumulated  almost  wholly 
on  their  margins,  then  we  must,  it  is  true,  make  our  measuring  rod,  i.  e.,  the  rate  of  sedi- 
mentation, much  greater,  but  we  must  also  take  the  sum  of  the  extreme  thickness  of  strata 
in  different  localities,  as  the  thing  to  be  measured.  We,  therefore,  make  another  esti- 


DENUDATION,   OR  GENERAL  EROSION.  277 

Some  may  object  to  this  estimate,  on  the  ground  that  geological 
agencies  were  once  much  more  active  than  now.  It  is  probable  that  this 
is  true  of  igneous  agencies,  since  these  are  determined  by  the  interior 
heat  of  the  earth,  and  this  has  evidently  been  decreasing.  It  is  probable 
also  that  this  is  true  of  the  chemical  agencies  of  water  in  disintegrating 
rocks  and  forming  soils,  since  chemical  effects  are  also  usually  increased 
by  heat.  But  there  is  good  reason  to  believe  that  the  mechanical  agen- 
cies of  water,  i.  e.,  its  erosive  power,  have  been  constantly  increasing 
with  the  course  of  time,  and  are  greater  now  than  at  any  previous  epoch 
except  the  Glacial  epoch. 

For  observe :  The  erosive  power  of  water  is  determined  entirely  by 
the  rapidity  of  circulation  of  air  and  water,  and  this  is  determinedly 
the  diversity  of  temperature  in  different  portions,  and  this  in  itjriurn 
by  the  size  of  continents  and  the  height  of  mountains.  Continei/s  and 
seas  are  two  poles  of  a  circulating  apparatus — at  one  pole  is  copdensa- 
tion,  at  the  other  evaporation.  In  proportion  to  condensation  are  also 
evaporation  and  circulation.  Now,  there  is  good  reason  to  believe  that, 
amid  many  oscillations,  there  has  been  throughout  all  geological  times 
a  constant  increase  in  the  size  of  continents  and  the  height  of  mount- 
ains. If  so,  then  the  circulation  of  air  and  water  has  been  becoming 
swifter  and  swifter ;  the  life-pulse  of  our  earth  has  beaten  quicker  and 
quicker,  and  therefore  the  waste  and  supply  (erosion  and  sedimentation) 
have  been  greater  and  greater.* 

We  therefore  return  to  our  estimate  of  30,000,000  years  with  greater 
confidence  that  it  is  even  far  within  limits  of  probability.  For,  1.  We 
have  taken  the  average  thickness  of  strata  at  2,000  feet,  while  it  is 
probably  much  more  2.  We  have  taken  the  Mississippi  as  an  average 
river,  and  therefore  the  present  rate  of  general  erosion  as  one  foot  in 
5,000  years :  it  is  probably  much  less.  3.  We  have  taken  the  rate  of 
erosion  in  previous  epochs  as  the  same  as  now,  while  it  is  probably 
much  less,  for  two  reasons :  1.  The  land-surface  to  be  eroded  was  smaller ; 
and,  2.  The  erosive  power  of  water  was  less.  Taking  all  these  things 
into  consideration,  the  time  necessary  to  produce  the  structure  which 
we  actually  find  is  enormously  increased. 

mate,  on  this  basis,  following  Mr.  Wallace.  Taking  the  whole  land-surface  (erosion  area) 
at  57,000,000  square  miles,  and  the  sedimentation  area  as  thirty  miles  wide  along  a  coast- 
line of  100,000  miles  (=3,000,000  square  miles),  then  with  an  erosion-rate  of  one  foot  in 
3,000  years  instead  of  5,000  years,  the  sedimentation  rate  would  be  nineteen  feet  in  the 
same  time,  or  one  foot  in  157  years.  But  the  extreme  thickness  of  strata  is  at  least 
177,000  fe»t.  This  would  take  28,000,000  years.— (Wallace,  Island  Life,  p.  210.) 

*  It  is  possible  that  the  erosive  effect  of  tides  in  earliest  geological  times,  far  greater 
than  now,  on  account  of  the  greater  proximity  of  the  moon,  is  an  element  which  should 
not  be  neglected  (Nature,  vol.  xxv,  p.  79).  But  this  probably  belongs  to  a  time  anteced- 
ent to  the  recorded  history  of  the  earth. 


278  DENUDATION,  OR  GENERAL  EROSION. 

But  even  this  gives  us  no  adequate  conception  of  the  time  involved 
in  the  geological  history  of  the  earth.  For  rocks  disintegrated  into 
soils,  and  deposited  as  sediments,  are  again  reconsolidated  into  rocks, 
lifted  into  land- surf  aces,  to  be  again  disintegrated  into  soils,  transported 
and  deposited  as  sediments.  And  thus  the  same  materials  have  been 
worked  over  and  over  again,  perhaps  many  times.  Thus  the  history  of 
the  earth,  recorded  in  stratified  rocks,  stretches  out  in  apparently  end- 
less vista.  And  still  beyond  this,  beyond  the  recorded  history,  is  the 
infinite  unknown  abyss  of  the  unrecorded.  The  domain  of  Geology  is 
nothing  less  than  (to  us)  inconceivable  or  infinite  time. 


PART  III. 
HISTORICAL  GEOLOGY; 


022,    THE  HISTORY  OF  THE  EVOLUTION"  OF  EARTH-STRUCTURE 
AND  OF  THE  ORGANIC  KINGDOM. 


CHAPTER  I. 
GENERAL  PRINCIPLES. 

GEOLOGY  is  the  history  of  the  evolution  of  earth-forms  and  earth- 
inhabitants.  There  are  certain  laws  underlying  all  development — cer- 
tain general  principles  common  to  all  history,  whether  of  the  indi- 
vidual, the  race,  or  the  earth.  We  wish  to  illustrate  these  general  prin- 
ciples in  the  more  unfamiliar  field  of  geology  by  running  a  parallel 
between  the  history  of  the  earth  and  other  more  familiar  forms  of 
history. 

1.  All  history  is  divided  into  eras,  ages,  periods,  epochs,  separated 
from  each  other  more  or  less  trenchantly  by  great  events  producing 
great  changes.     In  written  history  these  are  treated,  according  to  their 
importance,  in  separate  volumes,  or  separate  chapters,  sections,  etc. 
So  earth-history  is  similarly  divided  into  geological  eras,  ages,  periods, 
etc. ;  and  these  have  been  recorded  by  Nature  in  separate  rock-systems, 
rock-series,  rock-groups,  and  rock-formations.     In  geology  these  terms, 
both  those  referring  to  divisions  of  time  and  those  referring  to  divisions 
of  record,  are  unfortunately  loosely  and  interchangeably  used.     We 
shall  strive  jo  use  them  as  definitely  as  possible,  the  eras  and  the  cor- 
responding 'rick-systems  being  the  primary  divisions,  and  the  others 
subdivisions  in  the  order  mentioned. 

2.  In  all  history  successive  eras,  ages,  periods,  etc.,  usually  graduate 
insensibly  into  each  other,  though  sometimes  the  change  is  more  rapid 
and  revolutionary.     In  individual  history  childhood  usually  graduates 
into  youth,  and  youth  into  manhood;    yet  sometimes  a  remarkable 
event  determines  a  more  rapid  change.    In  social  and  political  life,  too, 
successive  phases  of  civilization  embodying  successive  dominant  prin- 
ciples usually  graduate  into  each  other ;  yet  great  events  have  some- 


280  GENERAL  PRINCIPLES. 

times  determined  exceptionally  rapid  changes  in  the  direction  or  the 
rate  of  movement.  So  also  is  it  in  geological  history.  The  eras, 
periods,  etc.,  usually  shade  more  or  less  insensibly  into  each  other ;  yet 
there  have  been  times  of  comparatively  rapid  or  revolutionary  change. 
In  all  history  there  are  periods  of  comparative  quiet,  during  which 
forces  of  change  are  gathering  strength,  separated  by  periods  of  more 
rapid  change,  during  which  the  accumulated  forces  produce  conspicu- 
ous effects. 

3.  Ages,  periods,  etc.,  in  all  history,  whether  individual,  political,  or 
geological,  are  determined  by  the  rise,  culmination,  and  decline  of  suc- 
cessively higher  dominant  forces,  principles,  ideas,  functions.  Thus, 
in  individual  development,  we  have  the  culmination,  first,  of  the  nutri- 
tive functions ;  then  of  the  reproductive  and  muscular  functions  ;  and, 
last,  of  the  cerebral  functions.  And  in  mental  development,  also,  we 
have  the  culmination,  first,  of  the  perceptive  faculties,  and  memory ; 
then,  the  imaginative  and  aesthetic  faculties ;  and,  last,  the  reflective 
faculties ;  the  first  gathering  and  storing  material,  the  second  vivifying 
it,  the  third  using  it  in  productive  mason- work  of  science.  In  social 
history,  too,  the  successive  culminations  of  different  phases  of  civiliza- 
tion have  been  the  result  of  the  introduction  and  culmination  of  suc- 
cessive dominant  principles  or  ideas — of  successive  social  forces  or 
functions.  So  has  it  been  in  geological  history.  The  great  divisions 
of  time,  especially  what  are  called  ages,  are  characterized  by  the  intro- 
duction and  culmination  of  successive  dominant  classes  of  organisms, 
for  these  are  the  highest  expression  of  earth-life.  Thus,  in  geology, 
we  have  an  age  of  mollusks,  an  age  of  fishes,  an  age  of  reptiles,  in 
which  these  were  successively  the  dominant  class. 

But  since  (Law  2)  successive  ages  graduate  more  or  less  into  and 
overlap  each  other,  we  might  expect,  and  do  indeed  find,  that  the 
characteristics  of  each  age  commence  in  the  preceding  age.  Each 
age  is  foreshadowed  in  the  previous  age.  The  same  is  true  of  all 
history. 

4. (In  all  history,  at  the  close  of  an  age,  the  characteristic  dominant 
principle  or  class  declines,  but  does  not  perish.  It  only  becomes  sub- 
ordinate to  the  succeeding  dominant  class  or  principle)  Thus,  to  illus- 
trate from  individual  history :  in  youth,  the  characteristic  faculties  of 
childhood,  viz.,  perception  and  memory,  decline,  and  become  subordi- 
nate to  the  higher  faculty  of  imagination,  and  this  in  turn  becomes  sub- 
ordinate to  the  still  higher  .faculty  of  productive  thought ;  and  thus  the 
whole  organism  becomes  higher  and  more  complex,  each  stage  of  devel- 
opment including  not  only  its  own  characteristic,  but  also,  in  a  subordi- 
nate degree,  those  of  all  preceding  stages.  The  same  is  true  of  social 
history.  Each  stage  of  social  development  absorbs  and  includes  the 
social  principles  and  forces  characteristic  of  previous  stages,  but  subor- 


GENERAL   PRINCIPLES.  281 

dinates  them  to  the  higher  principles  which  form  its  own  character- 
istic, and  thus  the  social  organism  becomes  ever  higher,  more  complex, 
and  varied. 

So  it  is  also  in  geologic  history.  When  the  dominance  of  any  class 
declines  at  the  end  of  an  age,  the  class  does  not  disappear,  but  remains 
subordinate  to  the  next  succeeding  and  higher  dominant  class,  and  the 
organic  kingdom,  as  a  whole,  becomes  successively  more  and  more  com- 
plex and  varied.  This  is  graphically  represented  by  the  accompanying 
diagram,  in  which  we  have  five  successive  ages  determined  by  the  cul- 
mination of  as  many  successive  dominant  classes. 


FIG.  253. — Diagram  illustrating  the  Rising,  Culmination,  and  Decline  of  Successive  Dominant 
Classes,  and  the  Increasing  Complexity  of  the  whole. 

5.  There  are  two  modes  of  determining  and  limiting  eras,  ages,  peri- 
ods, etc.,  in  geology,  viz.,  unconformity  of  the  rock-system  and  change 
in  the  life-system.)  In  written  human  history,  the  divisions  of  time  are 
recorded  in  separate  volumes,  chapters,  sections,  with  boards  or  blank 
spaces  between.     These  divisions  in  the  record  ought  to  correspond  to 
conspicuous  changes  in  the  character  of  the  most  important  contents. 

(So,  in  the  history  of  the  earth,  the  rock-systems,  rock-series,  rock-forma- 
tions, are  volumes,  chapters,  sections,  respectively,  more  or  less  com- 
pletely separated  from  each  other  by  unconformity,  indicating  blanks 
in  the  known  record ;  and  the  most  important  changes  in  the  contents, 
i.  e.,  in  the  life-system,  ought  to,  and  usually  do,  correspond  with  the 
unconformity  of  the  rock-system.  But  if  there  should  be  (as  there  is  in 
some  limited  localities)  a  discordance  between  these  two,  we  should  fol- 
low the  life-system  rather  than  the  rock-system,  the  contents  rather 
than  the  artificial  divisions  of  the  record) 

6.  As  in  human  history  there  is  a  general  onward  movement  of  the 
race,  and  yet  special  modifications  in  character  and  rate  in  each  coun- 
try ;  so  in  geology  there  has  been  a  general  march  of  evolution  of  the 
whole  earth  and  the  organic  kingdom,  and  yet  special  modifications  in 
character  and  rate  in  each  continent,  and  to  a  less  extent  in  different 
portions  of  the  same  continent.     The  great  eras,  ages,  and  periods,  be- 
long to  the  whole  earth  alike,  and  are  the  same  in  all  countries,  but  the 
epochs  and  the  smaller  divisions  of  time,  though  similar,  are  probably 
not  contemporaneous  in  different  countries.     This  fact  has  probably 
been  too  much  overlooked  by  geologists.     The  term  hom,otaxy  is  used 
to  express  identity  in  the  stage  of  evolution,  as  synchronism  is  used 
for  identity  of  time. 

Great  Divisions  and  Subdivisions  of  Time.— Eras.— It  is  upon  these 


282  GENERAL   PRINCIPLES. 

principles  that  geologists  have  established  the  divisions  of  time  and 
the  corresponding  divisions  of  strata. 

The  whole  history  of  the  earth  is  divided  into  five  eras,  with  corre- 
sponding rock-systems.  These  are:  1.  Archman  or  Eozoic *  era,  em- 
bodied in  the  Laurentian  system  ;  2.  Palaeozoic  \  era,  embodied  in  the 
Palaeozoic  or  Primary  system ;  3.  Mesozoic  I  era,  recorded  in  the  Sec- 
ondary  system ;  4.  Cenozoic,*  recorded  in  the  Tertiary  and  Quater- 
nary systems ;  and,  5.  The  Psychozoic  era,  or  era  of  Mind,  recorded  in 
the  recent  system. 

These  grand  divisions,  with  the  exception  of  the  last,  are  founded 
on  an  almost  universal  unconformity  of  the  rock-system,  and  a  very 
great  and  apparently  sudden  change  in  the  life-system,  a  change  affect- 
ing not  only  species  but  also  genera,  families,  and  even  orders.  Be- 
tween the  last  and  the  preceding,  it  is  true,  neither  the  unconformity 
of  the  rock-system  nor  the  change  in  the  life-system  is  so  great  as  in 
the  others ;  but  the  introduction  of  man  upon  the  scene  and  the  sweep- 
ing changes  which  are  now  going  on  through  his  agency  are  deemed 
sufficient  to  make  this  one  of  the  grand  divisions  of  time. 

We  have  already  seen  (p.  179)  that  unconformity  is  the  result  of 
deposit  of  strata  on  old  eroded  land-surfaces,  and  that  it  therefore 
always  indicates  an  oscillation  of  the  crust,  and  an  emergence  and  sub- 
mergence of  land.  In  every  such  case,  as  already  explained,  a  portion 
of  the  record  is  lost,  which  may  or  may  not  be  recovered  elsewhere. 
It  is  certain  that  if  the  lost  leaves  could  be  all  recovered,  and  the  rec- 
ord made  complete,  the  suddenness  of  the  break  in  the  life-system 
would  disappear.  Nevertheless,  it  is  also  certain  that  these  general 
unconformities  indicate  times  of  great  change  in  physical  geography, 
and  therefore  of  climate,  and  therefore  of  rapid  changes  of  organic 
forms ;  and  therefore,  also,  they  mark  the  natural  boundaries  of  the 
great  divisions  of  time. 

Ages. — Again,  the  whole  history  of  the  earth  is  otherwise  divided 
into  seven  ages,  founded,  with  perhaps  the  exception  of  the  first,  on  the 
culmination  of  certain  great  classes  of  organisms.  These  are :  1.  The 
Archcean  or  Eozoic  Age,  represented  by  the  Laurentian  system  of 
rocks ;  2.  The  Age  of  Mollusks,  or  Age  of  Invertebrates,  represented 
by  the  Silurian  series  of  rocks ;  3.  The  Age  of  Fishes,  represented  by 
the  Devonian  rocks  ;  4.  The  Age  of  Acrogens,  or  sometimes  called  the 
Age  of  Amphibians,  represented  by  the  Carboniferous  rocks ;  5.  The 
Age  of  Reptiles,  represented  by  the  Secondary  rocks ;  6.  The  Age  of 
Mammals,  by  the  Tertiary  and  Quaternary ;  and,  7.  The  Age  of 
Man,  by  the  recent  rocks. 

In  the  accompanying  diagram  (Fig.  254),  vertical  height  represents 

*  Dawn  of  animal  life.  f  01(*  life.  t  Middle  life.  *  Recent  life. 


GENERAL  PRINCIPLES. 


285 


time,  the  strong  horizontal  lines  divide  the  whole  into  eras,  while  al- 
lighter  lines,  where  necessary,  separate  the  ages.  The  shaded  ^pace- 
represent  the  origin,  the  increase  and  decrease,  in  the  course  of  time,  ol 


ANIMALS. 


PLANTS. 


BONIFEROUS 
D  E  V  0  N  I  A  N 
SILURIAN 


LAURENTIAN         SYSTEM 


Archaean 

Age. 


Psychozoic. 


Cenozoic. 


Mesozoic. 


Palaeozoic. 


Archaean, 
or  Eozoic. 


FIG.  254. 


the  great  dominant  classes  of  animals  and  plants.  To  illustrate :  The 
class  of  reptiles  commenced  in  the  uppermost  Carboniferous  increased 
to  a  maximum  in  the  Secondary,  and  again  decreased  to  the  present 
time.  It  will  be  seen  that  the  ages  correspond  with  the  eras,  except  in 
the  case  of  the  Palaeozoic  era.  This  long  and  diversified  era  is  clearly 
divisible  into  three  ages. 

Subdivisions. — The  subdivisions  of  eras  and  ages  into  periods  and 
epochs  are  founded,  as  already  explained  (p.  201),  on  less  general  un- 
conformity in  the  rock-system,  and  less  conspicuous  changes  in  the  life- 
system.  The  names  of  periods  are  often,  and  of  epochs  are  nearly 
always,  local,  and  therefore  different  in  different  countries.  We  will, 
of  course,  use  those  appropriate  to  American  geology.  The  table  on 
page  200  represents,  as  far  as  periods,  the  classification  used  in  this 
country.  We  have  added  epochs  only  in  the  uppermost  part,  viz.,  in 
the  Tertiary  and  Quaternary. 

We  give,  also  (Fig.  255),  an  ideal  diagram  of  the  principal  groups 
of  strata  which  we  shall  notice,  in  the  order  of  their 
superposition,  indicating  also  the  principal  places 
of  general  unconformity. 

The  terms  used  for  the  divisions  of  time,  and 
corresponding  divisions  of  rocks,  are  shown  in  the 
accompanying  schedule : 

Order  of  Discussion. — Many  geologists  take  up 


Time. 

Rocks. 

Eras    ) 
Ages  \  '  • 
Periods  .  . 

Systems. 
Series. 

Epochs  .  . 

Groups. 

282 


GENERAL  PRINCIPLES. 


Quater- 


Tapir,  Peccary,  Bison,  Llama 
Megatherium,  Mylodon,  Elephat. 


Pliohippus  Beds. 

Pliohippu*,  Hattodon,  Sot,  etc. 


Miohippus  Beds. 

Miohippus,  Diceratherium,  Thinohyus. 

Oreodon  Beds. 

Edentates,  Hyanodon,  Hyraeodon. 

Brontotherium  Beds. 

Mesohippux,  Menodws,  Elotherium. 


Diplacodon  Beds. 

Epihipput,  Amynodon. 

Dinoceras  Beds. 

Tinoeerat,  Uintatkerium.  Limnohyus, 
Orohippus,  Helaletet,  Colonocerat. 

Coryphodon  Beds. 
Eohippw>,  Monkeys,  Carnivores,  Ungu 
lates,  Tillodonts,  Rodents,  Serpents 


Laramie  Series. 


Upper  Cretaceous  of  N.  J. 

Hadrosaurua,  Dryptosaurut. 


'teranodon  Beds. 

Birds  with  Teeth,  TTesperomw,  IcJdhy- 
ornis.  Mosasaurs,  Pterodac- 

tyls, Plesiosaurs. 


Dakota  Group. 


)omanche  Group. 


A.tlanto8Huru8  Beds. 

Dinosaurs,  Apalosaurus,  Allotaurut, 
Nanosaunu.    Turtles.    Diplotaurus 


Connecticut  River  Beds. 

First  Mammals  (Marsupials),  (Droma- 

Dinosaur  F. 
Crocodiles  ( 


r  Footprints,  AmpTiit 
iiles  (Belodon). 


Permian. 

First  Reptiles. 


Coal- Measures. 


Snbcarbon  if  erou  s. 

First   known  Amphibian*   (Labyrin- 
thodonts). 


Jorniferous. 


?choharie  Grit. 
First  Fish  Fauna. 


Jpper  Silurian. 
Lower  Silurian. 


*rimordial. 


Huronian. 


-aurentian. 


No  Vertebrates 
except  in  the 
Uppermost 
Part. 


No  Distinct 
Organic 
Remains. 


FIG.  255.— Section  of  the  Earth's  Crust,  to  illustrate  Verte- 
brate Life  in  America.    (Slightly  modified  from  Marsh.) 


the  several  epochs  and 
periods  of  the  history  of 
the  earth  in  the  inverse 
order  of  their  occurrence. 
Commencing  with  a  thor- 
ough discussion  of  "  causes 
now  in  operation"  i.  e., 
geological  history  of  the 
present  time,  as  that  which 
is  best  known,  they  make 
this  the  basis  for  the  study 
of  the  epoch  immediate- 
ly preceding,  and  which, 
therefore,  is  most  like  it. 
Having  acquired  a  knowl- 
edge of  this,  the  student 
passes  to  the  preceding, 
and  so  on.  This  has  the 
great  advantage  of  pass- 
ing ever  from  the  better 
known  to  the  less  known, 
which  is  the  order  of  in- 
duction. Other  geologists 
prefer  to  follow  the  natu- 
ral order  of  events.  This 
has  the  great  advantage  of 
bringing  out  the  philoso- 
phy of  the  history — the 
law  of  evolution.  The 
first  method  is  the  best 
method  of  investigation; 
the  second  method  is  the 
best  method  of  presenta- 
tion. 

As  in  human  history, 
so  in  the  geological  histo- 
ry, the  recorded  events  of 
the  earliest  times  are  very 
few  and  meager,  but  be- 
come more  and  more  nu- 
merous and  interesting  as 
we  approach  the  present 
time.  Our  account  of  the 
Archaean  era  will,  there- 


LAUREXTIAN   SYSTEM   OF  ROCKS  AXD   ARCHAEAN  ERA.  285 

fore,  be  quite  general,  and  will  not  enter  into  any  subdivisions,  al- 
though this  era  was  very  long.  In  the  next  era  we  will  go  into  the  de- 
scription of  the  several  ages,  in  the  next  into  the  periods,  and  in  the 
next  even  into  the  epochs. 

Prehistoric  Eras. — Previous  to  even  the  dimmest  and  most  imper- 
fect records  of  the  history  of  the  earth  there  is,  as  already  said  (p.  278), 
an  infinite  abyss  of  the  unrecorded.  This,  however,  hardly  belongs 
strictly  to  geology,  but  rather  to  cosmic  philosophy.  We  approach  it 
not  by  written  records,  but  by  means  of  more  or  less  probable  general 
scientific  reasoning.  We  pass  on,  therefore,  without  pause  to  the  low- 
est system  of  rocks  containing  the  record  of  the  earliest  era. 


CHAPTER  II. 
LAURENTIAN  SYSTEM  OF  ROCKS  AND  ARCHAEAN  ERA. 

IT  is  one  of  the  chief  glories  of  American  geology  to  have  estab- 
lished this  as  a  distinct  system  of  rocks  and  a  distinct  era. 

It  had  been  long  known  that  beneath  the  lowest  Palaeozoic  rocks 
there  still  existed  strata  of  unknown  thickness,  highly  metamorphic 
and  apparently  destitute  of  fossils.  These  had  been  usually  regarded 
as  lowermost  Palaeozoic — as  the  earliest  defaced  leaves  of  the  Palaeo- 
zoic volume.  But  the  study  of  the  Canadian  rocks,  by  Sir  William 
Logan,  revealed  the  existence  of  an  enormous  thickness  of  highly-con- 
torted, metamorphic  strata,  everyivhere  unconformable  witli  the  overly- 
ing Primordial  or  lowest  Silurian.  More  recent  observations  show  this 
relation  not  only  in  Canada,  but  also  in  New  York,  on  Lake  Superior, 
in  Nebraska,  Montana,  Idaho,  Wyoming,  Colorado,  Utah,  Nevada, 
Texas,  New  Mexico,  and  Arizona.  Nor  is  it  confined  to  our  own  coun- 
try, for  the  same  unconformable  relation  has  been  found  by  Murchison 
on  the  west  coast  of  Scotland,  between  the  lowest  Silurian  (Cambrian) 
and  an  underlying  gneiss,  evidently  corresponding  to  the  Laurentian 
of  Canada.  Similar  rocks,  and  in  similar  unconformable  relation,  have 
been  found  underlying  the  primordial  in  Bohemia,  and  also  in  Sweden 
and  Bavaria,  and  many  other  places.  Such  general  unconformity 
shows  great  and  wide-spread  changes  of  physical  geography  at  this 
time,  and  therefore  marks  a  primary  division  of  time.  There  seems 
no  longer  any  doubt,  therefore,  that  it  should  be  regarded  as  a  distinct 
system. 

The  following  figures  (256,  257,  258)  give  the  relation  between  the 
Palaeozoic  and  the  Laurentian  in  New  Mexico,  in  Canada,  and  in 
Scotland. 


286 


LAURENTIAN  SYSTEM  OF  ROCKS 


These,  then,  are  the  oldest  known  rocks.     They  form  the  first  vol- 
ume of  the  recorded  history  of  the  earth.     Yet  they  evidently  are  not 


FIG.  256.— Section  across  Santarita  Mountain,  New  Mexico:  c.  Carboniferous;   8,  Silurian;   A,  \ 

Archaean;  m,  metalliferous  vein  (after  Gilbert).  .  .'  ;. 

I  '•* 

the  absolute  oldest ;  evidently  they  do  not  constitute  any  part  of*  the  /  , 
primitive  crust.     For  they  are  themselves  stratified  or  fragmental 


FIG.  257.— Section  showing  Primordial  unconformable  on  the  Archaean:  1,  Archaean  orLaurentian; 
2,  Primordial  or  Lowest  Silurian  (after  Logan). 

rocks,  and  therefore  formed  from  the  debris  of  other  rocks  still  older 
than  themselves ;  and  these  last  possibly  from  still  older  rocks. 


FIG.  258.— Diagram  Section,  showing  the  Structure  of  the  North  Highlands:  a,  Laurentian;  b,  Pri- 
mordial; c,  Lower  Silurian  (Jukes). 

we  search  in  vain  for  the  so-called  primary  rocks  of  the  original  crust. 
Thus  is  it  with  all  history.  No  history  is  able  to  write  its  own  begin- 
ning. 

Rocks. — There  is  nothing  very  characteristic  in  the  rocks  of  the 
Laurentian  system,  except  their  extreme  and  universal  metamorphism. 
They  do  not  differ  very  conspicuously  from  metamorphic  rocks  of  other 
periods;  consisting  probably  of  altered  sandstones,  limestones,  and 
clays.  They  are  all,  however,  very  much  contorted  and  very  highly 
metamorphic.  In  Canada  they  consist  mainly  of  the  schist  series, 
passing, on  the  one  hand  into  gneiss  and  granite,  and  on  the  other  into 
hornblendic*  gneiss,  syenites,  and  diorites ;  of  sandstones,  passing  into 
quartzites ;  and  of  limestones,  passing  into  marbles,  which  are  some- 
times even  intrusive.  These  together,  in  Canada,  form  a  series  of  rocks 
at  least  50,000  feet  thick. 

Interstratified  with  these  are  found  immense  beds  of  iron-ore  100  or 
more  feet  thick,  and  great  quantities  of  graphite,  sometimes  impreg- 
nating the  rocks,  and  sometimes  in  pure  seams.  In  rocks  of  this  age 
occur  the  great  iron-beds  of  Missouri,  of  New  Jersey,  of  Lake  Superior, 
and  of  Sweden ;  and  probably  the  mountains  of  iron  recently  found  in 


AND  ARCHAEAN  ERA.  287 

Utah.*    The  quantity  of  iron  found  in  these  strata  is  far  greater  than 
in  any  other.     It  may  well  be  called  the  Age  of  Iron. 


FIG.  259.— Contortion  of  Laurentian  Strata  (after  Logan). 


OL  a  & 

FIG.  260.  FIG.  261. 

The  above  figures  show  the  contortion  of  the  strata  (Fig.  259),  and 
the  mode  of  occurrence  of  the  iron  (Figs.  260,  261). 

Area  in  North  America. — 1.  These  strata  cover  the  greater  portion 
of  Labrador  and  Canada,  and  then,  turning  northwestward,  extend  to 
an  unknown  distance,  but  probably  to  the  Arctic  Ocean.  The  area  forms 
a  broad  V,  within  the  arms  of  which  is  inclosed  Hudson's  Bay.  It  may 
be  seen  on  map,  p.  291.  This  is  the  most  extensive  area  known  on  the 
continent.  2.  On  the  eastern  slopes  of  the  Appalachian  chain  un- 
doubted patches  are  found  as  far  south  as  Virginia,  and  a  larger  area 
in  this  region  is  referred  with  much  probability  to  the  same.  This  is 
shown  on  map,  p.  291.  Its  further  extension  southward  along  the 
chain  is  still  doubtful,  though  probable.  3.  In  the  Eocky  Mountain 
region  extensive  lines  and  areas  of  outcrop  are  known,  trending  in  the 
general  direction  of  the  chain,  and  forming  the  axis  of  the  great  ranges. 
4.  Several  small  patches  are  also  found  scattered  about  in  the  basin  of 
the  Mississippi,  apparently  exposed  by  erosion. 

Doubtless  the  Laurentian  rocks  are  far  more  extended,  but  covered 
and  concealed  by  other  and  later  rocks.  The  area  mentioned  is  the 
area  of  surface-exposure.  It  represents  so  much  of  Archaean  sea-bot- 
tom as  was  subsequently  raised  into  land,  and  not  afterward  again 
covered  by  sediments ;  or,  if  so  covered,  again  exposed  by  erosion. 

Physical  Geography  of  Archaean  Times. — As  these  are  stratified 
rocks,  they  must  have  been  formed  from  the  debris  of  still  older  rocks 
forming  the  land  of  that  time.  But  as  they  are  the  oldest  known  rocks, 
we  know  nothing  of  the  position  of  the  land  from  which  they  were 
formed.  But  since,  during  the  rest  of  the  geological  history,  the  con- 
tinent has  developed  from  the  north  toward  the  south,  it  seems  most 
probable  that  this  earliest  land  lay  still  farther  north,  perhaps  in  the 
North  Atlantic  region,  and  disappeared  when  the  Laurentian  area  was 
elevated  into  land. 

*  Newberry,  Genesis  of  Iron-Ores,  School  of  Mines  Quarterly,  1380. 


288 


LAURENTIAX  SYSTEM   OF  ROCKS  AXD  ARCHJEAN  ERA. 


Time  represented. — The  enormous  thickness  of  these  rocks  (50,000 
feet  in  Canada,  and  still  greater  in  Bohemia  and  Bavaria)  certainly  in- 
dicates a  very  great  lapse  of  time.  It  is  probable  that  the  Archaean 
era  is  longer  than  all  the  rest  of  the  recorded  history  of  the  earth  put 
together ;  and  yet,  precisely  as  in  the  beginnings  of  human  history,  the 
record  is  almost  a  blank.  The  events  are  few,  and  imperfectly  recorded. 
Evidences  of  Life. — We  have  already  explained  (p.  144)  how  iron- 
ore  is  at  present  accumulated.  We  have  there  shown  that  all  accumu- 
lations of  this  kind  now  going  on  are  formed  by  the  agency  of  organic 
matter.  It  is  almost  certain  that  the  same  is  true  for  all  times,  and 
therefore  that  iron-ore  accumulations  are  the  sign  of  the  existence  of 
organic  matter,  and  the  quantity  of  the  ore  accumulated  is  a  measure  of 
the  amount  of  organic  matter  consumed  in  doing  the  work.  The  im- 
mense beds  of  iron-ore  found  in  the  Laurentian  rocks  are,  therefore, 
evidence  of  the  existence  of  organisms  in  great  abundance.  That  these 
organisms  were  chiefly  vegetable^  we  have  the  further  evidence  derived 
from  the  great  beds  of  graphite  ;  for  graphite,  as  we  shall  see  hereafter, 
is  only  the  extreme  term  of  the  metamorphism  of  coal. 

Of  the  existence  of  animal  organisms  the  evidence  is  not  yet  com- 
plete, although  it  is  probable  that  the  lowest  forms  of  Protozoa,  such 

as  rhizopods,  were  abun- 
dant. We  have  seen  that 
limestones  are  abundant 
among  the  Laurentian 
rocks.  Now,  the  limestones 
of  subsequent  geological 
epochs  are  almost  wholly 
composed  of  the  accumula- 
ted shelly  remains  of  low- 
er organisms,  especially 
nullipores  and  coccoliths 
among  plants,  and  rhizo- 
pods among  animals. 

The  existence  of  rhizo- 
pods is  believed  by  some  to 
have  been  demonstrated. 
There  have  been  found 
abundantly,  in  the  Lauren- 
tian limestones  of  Canada,  of  Bohemia,  of  Bavaria,  and  elsewhere, 
large,  irregular,  cellular  masses,  which  are  believed  by  good  authorities 
to  be  the  remains  of  a  gigantic  foraminiferous  rhizopod.  The  sup- 
posed species  has  been  called  Eozoon  *  Canadense.  Fig.  262  is  a  sec- 


FIG.  262.— Section  of  the  Base  of  Specimen  of  EozoOn, 
x  f .    From'  a  photograph.    (After  Prestwich.) 


Dawn  animal. 


GENERAL  DESCRIPTION. 


289 


tion  of  an  Eozoonal  mass,  natural  size,  in  which  the  white  is  calcareous 
matter  supposed  to  have  been  secreted  by  the  rhizopod,  and  the  dark 
corresponds  to  the  supposed  animal  matter  of  the  rhizopod  itself  ;  and 
Fig.  263  a  small  portion  of  the  same,  magnified  so  as  to  show  the 
structure  of  the  cells. 

There  has  been,  and  is  still,  much  discussion  as  to  the  organic  or 
mineral  nature  of  these  curious  structures.    If  these  irregular  masses  be 

indeed  of  animal  origin,  it  is  

evident  that  they  belong  to  the 
lowest  forms  of  compound  pro- 
tozoa— lower  far  than  the  sym- 
metrically-formed foraminifera 
of  later  times.  It  is  precisely 
such  almost  amorphous 


in 


b  - 


.„  b 


masses  of  protoplasmic  matter 
that,  according  to  the  evolution 
hypothesis,  the  animal  kingdom 
might  be  expected  to  originate. 
Some  very  obscure  tracings, 

suggesting  the  pOSSlUe  existence    FIG.  263.-Diagram  of  a  Portion  of  EozoOn  cut  verti- 
"  cally:  A,  S,  V,  three  tiers  of  chamber*  communi- 

of    marine  worms,  have   been 


eating  with  one  another  by  slightly  constricted 
apertures;  a,  a,  the  true  shell- wall,  perforated  by 
numerous  delicate  tubes;  b,  b,  the  main  calcare- 


ous skeleton  ("  intermediate  skeleton");  c,  pas 
sage  of  communication  ("  stolon-passage  ")  from 
one  tier  of  chambers  to  another;  d,  ramifying 
tubes  m  the  calcareous  skeleton  (after  Carpenter). 


marine  worms, 

found  both  in  Canada  and  in 
Bohemia;  but  as  yet  we  have 
no  reliable  evidence  of  any  ani- 
mals higher  than  fhe  protozoa. 

It  is  impossible  to  say  that  other  animals  of  low  form  did  not  exist ; 
yet  the  absence  of  any  reliable  trace  in  rocks  not  more  metamorphic 
than  some  of  the  next  era,  which  are  crowded  with  fossils  of  many 
kinds,  seems  to  indicate  a  paucity,  if  not  an  entire  absence,  at  this  time, 
of  such  animals. 


CHAPTER  III. 

PRIMARY  OR  PALAEOZOIC  SYSTEM  OF  ROCKS  AND  PALAEOZOIC 

ERA. 

General  Description. 

THIS  is  a  distinct  system  of  rocks,  revealing  a  distinct  time-world — 
a  distinct  rock-system,  containing  the  record  of  a  distinct  life-system. 
The  rock-system  is  distinct,  being  everywhere  unconformed  to  the 
Laurentian  leloiv  and  the  Secondary  above — a  bound  volume — volume 
second  of  the  Book  of  Time.  The  life-system  is  also  equally  distinct, 

19 


290  PALAEOZOIC   SYSTEM   OF  ROCKS. 

being  conspicuously  different  from  that  which  precedes  and  that  which 
follows.  Whatever  of  life  existed  before,  its  record  is  too  imperfect  to 
give  us  a  clear  conception  of  its  character.  But  in  the  Palaeozoic  the 
evidences  of  abundant  and  very  varied  life  are  clear ;  more  than  20,000 
species  having  been  described.  It  stands  out  the  most  distinct  era  in 
the  whole  history  of  the  earth.  The  Archaean  must  be  regarded  as  the 
mythical  period.  Here,  with  the  Palaeozoic,  commences  the  true  dawn 
of  history. 

Rocks — Thickness,  etc. — The  rocks  of  this  system,  although  less 
powerful  than  the  preceding,  are  also  of  enormous  thickness  compared 
with  those  of  later  geological  times,  being  in  the  Appalachian  region 
about  40,000  feet;  in  Nevada,  about  40,000  feet;  in  the  Wahsatch 
Mountains,  33,000  feet  (King).  But  these  extreme  thicknesses  are  more 
local  than  in  the  case  of  the  Archaean.  It  is  believed  that  we  are  safe  in 
saying  that  the  time  represented  by  them  is  equal  to  all  subsequent  time 
to  the  present. 

There  is  nothing  very  characteristic  in  the  rocks  composing  Palaeo- 
zoic strata,  though  the  practiced  eye  may  often  distinguish  them  by 
their  lithological  character.  Though  strongly  folded  and  highly  meta- 
morphic  in  some  regions,  these  characters  are  not  so  universal  as  in  the 
Laurentian. 

In  the  United  States  the  rocks  of  the  whole  system  are  often  con- 
formable— for  example,  in  New  York  and  in  Utah.  In  Europe,  on  the 
contrary,  the  principal  divisions  are  usually  un conformable.  In  this 
country,  therefore,  the  subdivisions  are  founded  almost  wholly  on  change 
in  the  life-system ;  while  in  Europe  the  same  subdivisions  are  founded 
on  unconformity  of  the  rock-system,  as  well  as  change  in  the  life-sys- 
tem. Further,  in  this  country,  in  passing  from  Pennsylvania,  through 
New  York,  into  Canada,  we  pass  over  the  outcropping  edges  of  the 
whole  system,  from  the  highest  to  the  lowest,  and  finally  into  the  Lau- 
rentian (-Fig.  264).  This,  taken  in  connection  with  the  conformity  of 
the  rocks,  shows  that  during  the  Palaeozoic  the  continent  in  this  part 
was  successively  developed,  from  the  north  toward  the  south,  by  bodily 


FIG.  264.— Ideal  Section  north  and  south  from  Canada  to  Pennsylvania:  A,  Archaean;  L  $and 
US,  Silurian;  D,  Devonian;  C,  Carboniferous. 

upheaval  of  the  Laurentian  area  and  successive  exposure  of  contiguous 
sea-bottom.  In  Europe  the  oscillations  seem  to  have  been  more  fre- 
quent and  violent. 

Fig.  264  is  a  section  from  Pennsylvania  to  Canada,  showing  the 


GENERAL   DESCRIPTION. 


291 


relation  of  the  subdivisions  to  each  other,  and  the  manner  in  which 
they  lie  on  the  Archaean.  This  will  be  better  understood  if  the  map 
(Fig.  268)  on  page  297  be  at  the  same  time  carefully  examined. 


Area  in  the  United  States.— The  area  in  the  Eastern  United  States 
in  which  the  country  rock  belongs  to  this  system  is  seen  in  the  map 


292  PALAEOZOIC   SYSTEM   OF  ROCKS. 

above  (Fig.  265).  It  may  be  stated  roughly  to  embrace  all  that  part 
included  between  the  Great  Lakes  on  the  north,  the  Blue  Ridge  of  the 
Appalachian  chain  on  the  east,  the  Prairies  on  the  west,  and  Middle 
Alabama  and  Southern  Arkansas  on  the  south.  It  includes  the  richest 
portion  of  our  country.  Besides  this  great  continuous  area  there  are 
also  areas  of  imperfectly  known  size  and  shape  in  the  Eocky  Mount- 
ain region,  and  on  either  side  of  the  Sierra  Nevada. 

Physical  Geography  of  the  American  Continent.— At  the  beginning 
of  the  Palaeozoic  era  (Primordial)  the  land  was  substantially  the  Ar- 
ehcean  area,  already  described, plus  certain  areas  of  Archaean  rocks  which 
were  then  land,  but  have  been  subsequently  covered  by  later  deposits — 
minus  certain  Archaean  areas  which  have  been  subsequently  exposed 
by  erosion.  The  map  (Fig.  266)  *  is  an  attempt  to  represent  approxi- 
mately the  continent  of  that  time.  It  consisted  (1)  of  a  great  Northern 
land-mass  corresponding  roughly  to  the  Canadian  V-shaped  Archaean 


-. 


FIG.  266.— Map  of  Primordial  Times:  Black,  existing  seas  and  lakes;  li^ht  shade,  portions  of  the 
continent  then  covered  by  sea:  white  areas,  then  land;  when  limits  doubtful,  surrounded  by 
dotted  line.  In  case  of  area  2  the  land  extended  beyond  the  present  shore-line  to  an  unknown 
distance,  represented  by  the  white  dotted  line. 

area.  (2.)  An  Eastern  land-mass,  including  the  Appalachian  Archaean 
area,  but  extending  far  beyond  it  to  the  eastward  (for  the  coast  strata 
here  are  Cretaceous  and  Tertiary,  resting  directly  on  Archaean,  without 
any  Palaeozoic  between),  and  probably  beyond  the  present  limits  of  the 

*  A  map  similar  to  the  above,  but  containing  also  small  scattered  patches  of  Archaean 
exposures,  is  sometimes  spoken  of  as  an  Archaean  map  of  North  America,  or  map  of 
Archaean  land.  It  must  be  borne  in  mind,  however,  that  it  represents  indeed  land  of 
Archaean  strata,  but,  for  that  very  reason,  not  of  Archaean  time,  but  of  Silurian  time. 


GENERAL  DESCRIPTION. 

continent.  This  is  shown  by  the  white  dotted  line.  It  possibly  con- 
nected in  North  Atlantic  region  with  mass  No.  1.  (3.)  A  large  West- 
ern land-mass  of  unknown  shape  and  size  in  the  Basin  region.  (4.)  A 
large  land-mass  in  the  region  of  the  Colorado  and  Park  ranges.  There 
are  still  other  small  Archaean  areas,  but  these  were  probably  not  land 
at  that  time,  but  have  been  exposed  by  erosion.  Between  these  land- 
masses  on  the  north,  the  east,  and  the  west,  there  was  an  immense  sea 
— the  great  interior  Palaeozoic  Sea. 

The  reason  for  thinking  that  the  Eastern  land-mass  was  an  extensive 
one  is  the  immense  thickness  of  Palaeozoic  sediments  which  accumu- 
lated in  the  sea  along  its  western  border.  The  reason  for  thinking 
that  there  was  a  large  strip  of  land  in  the  Basin  region  is,  because  in 
all  that  region  the  Mesozoic  rocks  rest  directly  and  unconformably  on 
Archaean,  the  whole  Palceozoic  being  wanting. 

This  was  the  continent  at  the  beginning  of  the  Palaeozoic  era. 
From  this  as  a  nucleus  the  continent  somewhat  steadily  developed  until 
the  whole  of  the  Palaeozoic  area  was  added  to  it,  and  the  continent  be- 
came perhaps  somewhat  like  that  represented  on  page  470,  as  the  con- 
tinent of  Cretaceous  times. 

If  we  compare  the  Palaeozoic  rocks  of  the  Appalachian  region 
with  the  same  in  the  central  portion  of  the  Mississippi  basin,  we  ob- 
serve the  following  changes  as  we  go  westward  :  (a.)  The  rocks  in  the 
Appalachian  region  are  highly  metamorphic  ;  as  we  go  westward,  they 
become  less  and  less  so,  until  in  the  region  about  the  Mississippi  River 
they  are  wholly  unchanged,  (b.)  In  the  Appalachian  region  they  are 
strongly  and  complexly  folded ;  as  we  go  west,  these  folds  pass  into 
gentle  undulations,  which  die  away  into  horizontality  (see  section,  Fig. 
225,  on  p.  253).  (c.)  In  the  Appalachian  region  they  are  about  40,000 
feet  thick ;  as  we  go  west,  they  thin  out  until  the  whole  series  is  only 
4,000  feet  at  the  Mississippi,  (d.)  In  the  Appalachian  region  grits  and 
sandstones  and  shales  predominate  greatly  over  limestones ;  as  we  go 
west,  the  proportion  of  limestones  increases,  until  these  are  the  predomi- 
nating rocks.  These  four  changes  are  closely  connected  with  each  other, 
and  all  with  the  formation  of  the  Appalachian  chain,  as  we  have  already 
explained  in  the  chapter  on  Mountain-Formation  (p.  258). 

Subdivisions. — The  Palaeozoic  era  is  divided  into  three  ages,  which 
are  embodied  in  three  distinct  subordinate  rock-systems.  These  ages 
are  each  characterized  by  the  dominance  of  a  great  class  of  organisms. 
They  are :  1.  The  Silurian  System,  or  Age  of  Invertebrates,  or  some- 
times called  Age  of  Mollusks ;  2.  The  Devonian  System,  or  Age  of 
Fishes ;  and,  3.  The  Carboniferous  System,  or  Age  of  Acrogens  and 
Amphibians.  These  are  three  chapters  in  the  Palaeozoic  volume. 

These  three  systems  are  generally  conformable  with  each  other  in 
the  Palaeozoics  of  the  United  States,  as  we  have  already  shown,  but 


294:  PALEOZOIC   SYSTEM   OF  ROCKS. 

elsewhere  they  are  often  unconformable.  Before  taking  up  the  first  in 
the  order  of  time,  viz.,  the  Silurian,  it  is  necessary  to  say  something  of 
the  interval  which  in  our  record  separates  the  Archaean  from  the  Palaeo- 
zoic era. 

The  Interval. 

We  have  already  seen  that  the  lowest  Silurian  lies  unconformably 
on  the  upturned  and  eroded  edges  of  the  crumpled  strata  of  the 
Laurentian.  We  have  also  shown  (page  179)  that  unconformability 
indicates  always  an  oscillation  of  the  earth's  crust  at  the  observed 
place.  More  definitely  it  indicates  an  upheaval,  by  which  the  lower 
series  of  rocks  became  land-surface,  and  were  at  the  same  time,  per- 
haps, crumpled ;  then  a  long  period  unrecorded  at  that  place,  during 
which  the  land  was  eroded  and  the  edges  of  the  crumpled  rocks  were 
exposed ;  then  a  subsidence,  and  the  deposit  of  the  upper  series  of  rocks 
on  these  exposed  edges.  Now,  oscillation  necessitates  increase  and  de- 
crease of  land-surface.  Evidently,  therefore,  such  increase  and  decrease 
of  land-surface  took  place  in  the  unrecorded  interval  between  the 
Archaean  and  Palaeozoic  eras ;  and  the  length  of  this  unrecorded  inter- 
val is  measured  by  the  amount  of  erosion  which  the  Laurentian  under- 
lying the  lowest  Palaeozoic  has  suffered.  We  have  stated  that  the  land 
at  the  beginning  of  the  Silurian  age  was  approximately  the  Laurentian 
area.  The  shore-line  of  the  earliest  Palaeozoic  sea  was  the  line  of  junc- 
tion between  the  Silurian  and  Laurentian  (see  map,  page  291).  But 
this  was  not  the  shore-line  at  the  end  of  the  Archcean  time.  Evidently 
this  shore-line  was  much  farther  south ;  evidently  the  land-area  was 
much  greater  at  the  end  of  the  Archaean  than  at  the  beginning  of  the 
Silurian.  The  Archaean  era  was  closed  by  the  upheaval  into  land- 
surface  and  the  crumpling  of  the  strata  of  the  whole  Laurentian  area, 
and  much  more.  Then  followed  an  interval  of  which  we  know  noth- 
ing, except  that  it  was  of  long  duration,  during  which  the  crumpled 
Laurentian  strata  forming  the  then  land-surface  were  deeply  eroded. 
Then,  at  the  end  of  this  interval  came  a  subsidence,  down  to  the  shore- 
line already  indicated  as  the  Silurian  shore-line,  and  the  Silurian  age 
commenced,  its  first  sediments  being  of  course  deposited  on  the  exposed 
edges  of  the  submerged  Laurentian  rocks. 

I  have  attempted  to  illustrate  these  facts  by  the  following  diagrams 
(Fig.  267),  in  which  the  last,  e,  represents  a  north  and  south  ee'ction  of  the 
Archaean  and  Palaeozoics  of  the  Canadian  border,  and  southward  to  Penn- 
sylvania. The  crumpled  and  eroded  strata  of  the  Archaean  are  seen  to 
underlie  unconformably  the  primordial  rocks  for  some  distance  south — 
how  far  we  know  not.  This  is  the  present  condition  of  things.  How 
they  came  so  is  shown  in  a,  #,  c,  and  d.  In  a,  we  have  the  supposed 
condition  of  things  in  Archaean  times.  The  position  of  the  land  was 
somewhere  northward — we  know  not  where.  In  &,  a  large  portion  of 


THE   INTERVAL. 


295 


Archsean  marginal  sea-bottom  was  raised  into  land,  and  at  the  same 
time  crumpled.     In  c,  the  same  was  eroded,  so  that  the  edges  of  strata 


Archaean  Land. 


rfrch  cean 


Sea 


Land  of  thu  Interval  eroded. 

m 

iA> — ixv^ 


Primordial  Land. 


9r^  "^ 


Sea 


Existing  condition. 


FIG.  267.— Ideal  Section,  showing  how  Unconformity  was  produced  on  the  Canadian  Border:  S  L, 

sea-level. 

were  exposed.  This  was  during  the  interval  In  d,  the  land  sank 
again  to  the  primordial  shore-line,  and  the  Palaeozoic  era  commenced. 
During  the  Palaeozoic  the  land  gradually  rose  so  as  to  expose  successive 
sea-bottoms  of  Cambrian,  Silurian,  Devonian,  and  Carboniferous  ages. 
It  has  remained  substantially  in  this  condition  ever  since. 

We  have  spoken  thus  far  only  of  the  uncomformity  of  the  New 
York  rocks  on  the  Canadian  rocks.  This  phenomenon  may  be  ex- 
plained, as  we  have  seen,  by  local  oscillations,  with  increase  and  decrease 
of  land-area  during  the  lost  interval.  But,  when  we  remember  that  the 
same  unconformity  is  found  in  the  most  widely-separated  localities, 
over  the  whole  area  of  the  United  States,  we  are  forced  to  the  conclu- 
sion that  the  lost  interval,  as  compared  with  the  Silurian,  was  probably 
a  continental  period — a  period  of  widely-extended  land  composed  of 
Laurentian  rocks.  The  whole  of  this  land  disappeared  by  submergence 
at  the  beginning  of  the  Primordial,  except  the  Canadian  area,  a  large 
area  east  of  the  Appalachian,  and  probably  a  considerable  area  in  the 
Basin  region,  and  perhaps  a  few  islands  or  larger  areas  in  the.  Primordial 
seas  between,  as  shown  in  map,  Fig.  266. 

In  all  speculations  on  the  origin  of  the  animal  kingdom  by  evolu- 
tion, it  is  very  necessary  to  bear  in  mind  this  lost  interval,  for  it  was 
evidently  of  great  duration. 


296  PALEOZOIC   SYSTEM   OF  ROCKS. 

SECTION  1. — SILURIAN  SYSTEM  :  AGE  OF  INVERTEBRATES. 

The  Rock-System.— The  rocks  of  this  age  have  been  carefully  studied 
in  England,  by  Sedgwick  and  Murchison ;  in  Russia  and  Sweden,  by 
Murchison ;  in  Bohemia,  by  Barrande ;  and  in  New  York,  by  Hall. 
The  divisions  and  subdivisions  established  by  these  geologists  have  be- 
come the  standard  of  comparison  elsewhere.  The  system  was  first 
clearly  defined  by  Murchison  in  Wales.  The  name  Silurian  was  given 
by  Murchison  to  the  rocks  of  the  whole  age.  The  name  Cambrian  was 
given  by  Sedgwick  to  the  lower  part.  We  have  called  the  whole  age 
Silurian,  but  the  great  thickness  and  exceptional  importance  of  the 
lower  part  have  induced  many  geologists  to  erect  this  into  a  distinct 
system  equivalent  to  the  Silurian,  and  to  call  it  Cambrian,  or  Pri- 
mordial. We  shall,  however,  make  Cambrian,  or  Primordial,  one  of 
the  primary  divisions  of  the  Silurian  age. 

Subdivisions. — The  following  table  gives  the  divisions  and  subdi- 
visions of  the  rocks  and  the  corresponding  periods  of  the  age  in  this 
country : 


Silurian  Age  or  Age  , 
of  Invertebrates.. 


i  Lower  Helderbcrg  Period. 
Salina  " 

Niagara 

Lower  Silurian  .........  \  £renton 

.     I  Canadian 


Cambrian  or  Primordial. 


The  larger  divisions,  viz.,  Primordial,  Lower  Silurian,  and  Upper 
Silurian,  are  generally  recognized.  The  subdivisions  are  local,  each 
country  having  its  own ;  but  they  are  synchronized,  as  far  as  possible, 
by  comparison  of  fossils.  As  we  shall  be  compelled  to  treat  the  age 
together  as  a  whole,  we  shall  use  the  word  Silurian  to  express  the  rocks 
of  the  whole  age,  although  we  freely  admit  the  superior  importance  of 
the  Primordial,  or  Cambrian,  as  compared  with  other  divisions. 

Character  of  the  Rocks. — The  Silurian,  like  nearly  all  rocks,  are 
greatly  disturbed  and  metamorphosed  in  mountain-regions,  though 
less  so  than  the  Laurentian ;  but  in  Sweden  and  Russia,  and  in  the 
valley  of  the  Mississippi,  they  are  found  in  their  original  horizontal 
position,  and  not  greatly  changed  from  their  original  sedimentary  con- 
dition. 

Area  in  America. — By  turning  to  the  map  (page  291)  it  will  be  seen  : 
1.  That  the  Silurian  is  attached  to  the  Canadian  Laurentian  nucleus  as 
an  irregular  border  on  the  outer  side  of  the  V-shaped  area ;  2.  Again, 
the  Appalachian  Laurentian  region  is  also  bordered  on  the  west  side  by 
Silurian ;  3.  Also  we  observe  large  patches  in  the  interior — one  about 
Cincinnati,  another  occupying  the  southern  portion  of  Missouri  and 
northeastern  portion  of  Arkansas,  and  one  in  Middle  Tennessee ;  4. 


SILURIAN   SYSTEM:   AGE   OF  INVERTEBRATES. 


297 


Also  as  narrow  bands  on  the  flanks  of  nearly  all  the  Rocky  Mountain 
ranges ;  5.  Also  considerable  areas  in  Basin  region  the  outlines  of  which 
are  little  known. 

Physical  Geography. — At  the  beginning  of  the  Silurian  (Primor- 
dial), as  already  said,  the  land  was  approximately  the  Laurentian  area 
(Fig.  266).  The  Silurian,  which  embraces  the  great  V-shaped  Lau- 
ren tia  area  on  the  southeast,  south,  and  southwest,  was  then  the  sea- 
bottom  border  of  the  coast'  of  the  Primordial  continent.  The  Silurian 
bordering  the  Appalachian  Laurentian  was  also  then  a  sea-bottom 
bordering  the  Primordial  continent  in  that  region.  It  is  probable, 
also,  that  the  Silurian  of  the  Rocky  Mountain  region  also  borders 
Laurentian  areas,  and  these  areas  represent  Primordial  continents,  and 
the  Silurian  border  the  marginal  sea-bottom  of  that  time.  The  other 
patches  mentioned  in  the  interior  were  probably  bottoms  of  open  seas. 

Now,  the  Silurian  area  represents  so  much  of  Silurian  sea-bottoms 
as  were  raised  into  land-surfaces  during  or  at  the  end  of  Silurian  times, 
and  not  subsequently  covered  by  sea.*  Therefore,  at  the  beginning  of 
Silurian  times  the  land  was  the  Laurentian  area ;  while  at  the  end  of 


sc 


FIG.  268.— Geological  Map  of  New  York:  a,  Archaean:  PS,  Primordial:  LS,  Lower  Silurian;  US, 
Upper  Silurian;  d,  Devonian;  SC,  Subcarboniferous;  C,  Coal-measures. 

the  Silurian  times  the  land  was  increased  by  the  addition  of  the  Silurian 
area.     This  addition  was  not  all  made  at  once,  but  very  gradually. 

*  This  is  true  as  a  broad,  general  fact ;  but  patches  of  Silurian  may  also  be  exposed 
by  removal  of  later  deposits  by  erosion. 


298  PALAEOZOIC   SYSTEM   OF  ROCKS. 

The  steps  of  this  increase  have  been  carefully  studied  in  New  York. 
The  map  (Fig.  268)  shows  the  principal  successive  steps,  as  does  also 
the  section  (Fig.  264)  with  which  it  should  be  compared.  Inspec- 
tion of  these  figures  shows  not  only  the  Silurian  bordering  the  Lau- 
rentian,  but  the  rocks  of  the  several  periods  bordering  each  other 
successively ;  so  that  in  walking  from  Pennsylvania  to  Canada,  or  to 
the  Adirondack  Mountains  of  New  York,  we  successively  walk  over  the 
Carboniferous,  the  Devonian,  the  Silurian,  and  the  Laurentian ;  and 
in  the  Silurian  over  rocks  of  the  successive  periods,  from  the  highest 
to  the  lowest.  This  plainly  shows  that  during  Silurian  times  the  con- 
tinent (Laurentian  area)  was  slowly  upheaved,  and  contiguous  sea-bot- 
toms successively  added  to  the  land,  and  the  shore-line  gradually  pushed 
southward  from  the  Canadian  region,  and  probably  westward  from  the 
land-mass  along  the  Appalachian.  Of  course,  therefore,  the  oldest 
Silurian  shore-line  was  the  most  northern  and  eastern.  This  is  the 
primordial  leach. 

Primordial  Beach  and  its  Fossils. — As  already  stated,  the  element- 
ary character  of  this  treatise  renders  it  impossible  to  take  up  separately 
the  several  periods  of  this  age.  We  must  confine  ourselves  to  a  general 
description  of  the  age  only.  But  there  is  so  peculiar  and  special  an 
interest  connected  with  the  dawn  of  life  on  the  earth,  that,  before  taking 
up  the  life-system  of  the  whole  age,  it  seems  necessary  to  say  something 
of  the  earliest  fauna. 

We  have  seen  that  at  the  beginning  of  Silurian  times  a  large  V- 
shaped  mass  of  land  occupied  the  region  now  embraced  by  Canada  and 
Labrador,  and  stretched  northwestward  to  an  unknown  distance,  the  two 
arms  of  the  V  being  nearly  parallel  to  the  two  present  shores  of  the 
American  Continent;  further,  that  a  land-mass  of  extent  unknown 
occupied  the  position  of  the  eastern  slope  of  the  Appalachian  chain ; 
also,  that  land  of  unknown  extent  occupied  the  position  of  the  Rocky 
Mountains  and  Basin  region ;  and  the  continent  was  thus  early  sketched 
out.  Now,  southward  of  the  first-mentioned  land-area  and  between  the 
other  two  there  was  a  great  interior  sea,  which  we  have  called  the  In- 
terior Palceozoic  Sea.  The  shores  of  that  sea  beat  upon  the  continental 
masses  north,  east,  and  west,  and  accumulated,  on  exposed  places,  a 
beach.  Patches  of  that  earliest  beach  still  remain.  They  are  found, 
of  course,  closely  bordering  the  Laurentian  rocks,  Canadian  and  Appa- 
lachian, and  lying  unconformably  upon  them.  They  are  the  primordial 
sandstones  and  slates  of  Canada,  New  York,  Pennsylvania,  Virginia, 
and  probably  Tennessee  and  Georgia.  The  fact  that  these  are  indeed 
remnants  of  a  beach  is  proved  by  the  existence,  in  almost  every  part, 
of  shore-marks  of  all  kinds — such  as  ripple-marks,  sun-cracks,  worm- 
tracks,  worm -borings,  broken  shells,  etc. 

This,  then,  is  the  old  primordial  beach.    It  is  of  the  extremest  inter- 


SILURIAN   SYSTEM:   AGE   OF  INVERTEBRATES. 


299 


FIG.  271. 


FIG.  278. 


FIG.  274. 


FIG.  275. 


FIG.  276 


FIG.  279. 


FIGS.  269-279.—  AMERICAN  CAMBRIAN  FOSSILS  (after  Walcott  and  White):  269.  Protyptis  Hitch 
™£'  IrSi    27?.  z.aca"thoide*  typical  is.  x  2.    271.  Agnostus  interstrictus.    272.  F6r^illa  Troy 
ensis     273   Orthisina  transversa.    274.  Kutorgina  pannnla-a,  front  view;  a',  side  view.    275 


?elata     |~9   Ob  /'ll 


Auiorgina  pannnla— a,  front  view;  a'  side  view.    275. 
simplex.    277.  Hyolithes  primordialis.    278.  Lingulella 

^^S^» 

,T  Y  W  «  »*   • 


300 


PALEOZOIC   SYSTEM  OF  ROCKS. 


est  to  the  geologist  because  it  marks  the  outline  of  the  earliest  Silurian 
sea,  and  contains  the  remains  of  the  earlest  Silurian  fauna.  Indeed, 
we  may  say  it  contains  the  remains  of  the  earliest  known  fauna.  It  is 
true,  the  lowest  Rhizopods  probably  existed  in  Archsean  times,  but 
these  can  not  be  said  to  constitute  a  fauna.  With  the  very  commence- 
ment of  Silurian  times,  however,  we  find,  at  once  a  considerable  variety 
of  animal  forms. 

"What,  then,  was  the  character  of  this  earliest  fauna  and  flora  ?  If 
we  could  have  walked  along  that  beach  when  it  was  washed  by  pri- 
mordial seas,  what  would  we  have  found  cast  ashore  ?  We  ivould  have 
found  the  representatives  of  all  the  great  types  of  animals  except  the 
vertebrata.  The  Protozoa  were  then  represented  by  sponges  and 
Ehizopods;  the  Radiates  by  Hydrozoa  (graptolites)  (Fig.  276)  and  Cys- 
tidean  Crinoids ;  the  mollusks  by  Brachiopods,  Lamellibranchs,  Gas- 
teropods  (Pleurotomaria),  Pteropods  (Figs.  272-279),  and  even  Cepha- 
lopods  (orthoceras) ;  and  the  Articulates  by  Crustaceans  (trilobites, 
etc.)  (Figs.  269-271)  and  Worms  (Fig.  281).  Plants  are  represented  by 
Fucoids.  These  widely-distinct  classes  are  already  clearly  differentiated 
and  somewhat  highly  organized.  Nor  is  the  fauna  a  meager  one  in 
number  of  species.  In  the  United  States  and  Canada  alone  about  400 
species  are  already  known  in  the  primordial,  of  which  nearly  100  are 
trilobites ;  and  in  the  lowest  zone  of  the  primordial,  viz.,  Olenellus 
beds,  there  are  134  species,  of  which  55  are  trilobites  (Walcott).  About 


FIG.  280. 


FIG.  283. 


FIG.  286. 


FIG.  288. 


FIGS.  280-288.— FOREIGN  PRIMORDIAL  FOSSILS:  280.  Oldhamia  antiqua,  probably  a  plant.  281. 
Arenicolites  didymus,  worm-tubes.  282.  Lingulella  ferruginea.  283.  Theca  Davidii.  284. 
Modiolopsis  solvensis.  285.  Orthie  Hicksii.  286.  Obolella  sagittalis.  287.  Hymenocaris  vermi- 
cauda.  288.  Olenus  macrurus. 

a  dozen  species  of  plants  are  also  known.     When  we  recollect  the  great 
age  of  these  rocks  and  their  usual  metamorphism,  and  the  fragmentary 


SILURIAN   SYSTEM:   AGE   OF   INVERTEBRATES. 


301 


character  of  all  fossil  faunas,  it  seems  certain  that  great  abundance  and 
variety  of  life  existed  already  in  these  early  seas.  Of  this  life  the  tri- 
lobites,  by  their  size,  their  abundance,  their  variety,  and  their  high 
organization,  must  be  regarded  as  the  dominant  type.  Among  the 
largest  trilobites  known  at  all  are  some  from  this  period.  The  Para- 
doxides,  represented  in  Figs.  289  and  290,  attained  a  length  of  twenty 
inches.  English  beds  of 
the  same  age  furnish 
specimens  of  the  same 
genus  two  feet  long. 

We  give  in  the  above 
figures  a  few  of  the  more 
remarkable  primordial 
forms  taken  from  the 
rocks  of  this  country, 
and  of  foreign  countries. 
They  are  intended  only 
to  give  a  general  idea  of 
the  fullness  and  variety 
of  the  primordial  life; 
the  affinities  of  these  fos- 
sils will  be  discussed 
hereafter. 

General  Remarks  on  First  Distinct  Fauna. — There  are  several 
points  of  great  philosophic  interest  suggested  by  the  nature  of  these 
first  organisms : 

1.  Plants  in  this,  and  in  all  other  geological  periods,  are  far  less 
numerously  represented  in  a  fossil  state  than  animals.    This  can  not  be 
because  animals  were  more  abundant  than  plants,  for  since  the  animal 
kingdom  subsists  on  the  vegetable  kingdom,  and  since  every  animal 
consumes  many  times  its  own  weight  of  food,  plants  must  have  been 
always  more  abundant  than  animals.     The  true  reason  of  the  greater 
abundance  of  animal  remains  is  to  be  found  in  the  fact  that  the  hard 
parts  of  animals  are  far  more  indestructible  than  any  portion  of  vege- 
table tissue. 

2.  At  the  end  of  the  Archaean  times — when  the  Archaean  volume 
closed — we  find,  if  any,  only  the  lowest  Protozoan  life.     But  with  the 
opening  of  the  next  era,  apparently  with  the  first  pages  of  the  next 
volume,  we  find  already  all  the  great  types  of  structure  except  the 
vertebrata.     And  these  are  not  the  lowest  of  each  type,  as  might  have 
been  expected,  but  already  trilobites  among  Articulata,  and  Cephalo- 
pods  among  Mollusca — animals  which  can  hardly  be  regarded  as  lower 
than  the  middle  of  the  animal  scale. 

We  must  not  hastily  conclude,  however,  that  these  widely-divergent 


FIG.  289.— Paradoxides  Bohcmi- 
cus,  Foreign. 


FIG.  290.—  Paradoxides 
Harlani,  x  £  (after 
Rogers),  American. 


302  PALEOZOIC   SYSTEM   OF   ROCKS. 

and  highly-organized  types  originated  together  at  once.  We  must  re- 
member that  between  the  Archaean  and  Palaeozoic  there  is  a  lost  inter- 
val of  enormous  duration.  Evidently,  therefore,  the  Primordial  fauna 
is  not  the  actual  first  fauna.  Evidently  we  have  not  yet  recovered  the 
leaves  in  which  is  recorded  the  gradual  differentiation  of  these  widely- 
distinct  types.  All  this  must  have  taken  place  during  the  lost  in- 
terval. 

But  if,  on  the  other  hand,  we  suppose,  as  many  do,  that  evolution 
proceeds  always  "  with  equal  steps,"  then  we  are  forced  to  the  very  im- 
probable conclusion  that  the  lost  interval  is  equal  to  all  geological  times 
which  followed  to  the  present ;  for  the  differentiation  of  types  which 
occurred  during  that  interval  is  equal  in  value  to  all  that  has  taken 
place  since. 

Therefore,  we  are  compelled  to  admit  that  there  have  been  in  the 
history  of  the  earth  periods  of  rapid  change  in  physical  geography,  and 
periods  of  comparative  quiet  in  this  respect ;  that,  corresponding  with 
these,  there  have  been  also  periods  of  rapid  evolution  of  the  organic 
kingdom,  developing  new  forms,  and  periods  in  which  forms  are  more 
stationary.  The  periods  of  rapid  change  are  marked  by  unconformity, 
and  are  therefore  unfortunately  often  lost. 

As  we  proceed,  we  will  probably  find  many  examples  of  rapid  change 
which  must  be  accounted  for  in  a  similar  manner. 

General  Life-System  of  the  Silurian  Age. 

After  this  rapid  sketch  of  the  first  fauna,  we  now  take  up  the  gen- 
eral life-system  of  the  whole  age. 

There  were  evidently  extraordinary  abundance  and  variety  of  life 
in  the  Silurian.  These  early  seas  literally  swarmed  with  living  beings. 
The  quantity  and  variety  of  life— fftie  number  of  individuals  and  of 
species — were  probably  not  less  than  at  the  present  time  ;  though  or- 
ders, classes,  and  departments,  were  less  diversified.  Over  10,000  spe- 
cies have  been  described  from  the  Silurian  alone  (Barrande) ;  and 
these  must  be  regarded  as  only  a  small  fragment  of  the  actual  fauna 
of  the  age.  In  certain  favored  localities,  the  number  of  species  found 
in  a  given  area  of  a  single  stratum  will  compare  favorably  with  the 
number  now  existing  in  an  equal  area  of  our  present  sea-bottoms.  Yet, 
in  all  this  teeming  life  there  is  not  a  single  species  similar  to  any  found 
in  any  other  geological  time.  And  not  only  are  the  species  peculiar, 
but  even  the  genera,  the  families,  and  the  orders,  are  different  from 
those  now  existing. 

We  can  give  only  a  very  brief  sketch  of  this  early  life,  touching  only 
the  most  salient  points,  especially  such  as  throw  light  on  the  great 
question  of  evolution. 


GENERAL   LIFE-SYSTEM   OF   THE   SILURIAN  AGE.  393 


bilobata 


FIG.  296. 

,:  291   Sphenothallns  angnstifolius.    292.  Buthotrephls 
Buthotrephis  gracihs.    295.  Arthrophycus  Harlani.     296.  Cruziana 


304 


PALAEOZOIC   SYSTEM   OF   ROCKS. 


Plants. 

With,  the  exception  of  a  few  small  land-plants,  ferns,  and  club- 
mosses,  recently  found  in  the  Middle  Silurian  of  both  this  country  and 
Europe,*  and  of  which  we  shall  speak  again,  the  only  plants  yet  found 
are  the  lowest  forms  of  cellular  cryptogams,  viz.,  marine  algce  or  sea- 
weeds. It  is  difficult,  from  the  impressions  left  by  these  to  determine 
genera,  much  more  species,  with  any  degree  of  certainty.  We  shall, 
therefore,  call  them  by  the  general  somewhat  indefinite  name  of  Fu- 
coids  (Fucus,  tangle  or  kelp),  or  Fucus-like  plants.  As  already  stated, 
plants  are  far  less  abundantly  and  perfectly  preserved  than  animals,  on 
account  of  their  want  of  a  skeleton. 

Animals. 

Protozoans. — The  large,  irregular  masses  which  are  called  Eozoon 
seem  entirely  characteristic  of  Archaean  times.     If  they  are  indeed  of 
_  animal   origin,   they 

are  replaced  in  the 
Silurian  age  by  more 
regular  forms  which 
are  usually  called 
sponges.  Of  these, 
the  most  character- 
istic Silurian  genera 
are  Stromatopora 
and  Eeceptaculitis 
(Figs.  297  -  303). 
They  seemed  to  have 
formed  large  coral- 
line masses, which  are 
now  regarded  either 
as  hydrocorals  (Stro- 
matopora) or  as  com- 
pound Rhizopods 
(Receptaculitis). 

Radiates,  Corals.— Corals  were  very  abundant,  forming  often  whole 
rock-masses,  as  if  they,  while  living,  formed  reefs.  These,  if  they  in- 
dicate warm  seas,,  show  a  great  uniformity  of  temperature,  since  they 
are  found  in  all  portions  of  the  earth  alike. 

The  corals  of  the  Silurian  age  belong  principally  to  three  families, 
viz.,  Cyathophylloids,  or  cup-corals  ;  Favositidce,  or  honey-combed  cor- 
als ;  and  Halysitida  or  chain-corals.  They  are  remarkable  in  not 


FIG.  297.— Stromatopora  rugosa. 


*  Lesquereux,  American  Journal  of  Science,  1878,  vol.  xv,  p.  149. 


SILURIAN  ANIMALS. 


305 


usually  being  profusely  and  widely  branched  like  most  modern  corals, 
but  consisting  mostly  of  masses  of  parallel  or  nearly  parallel  columns. 
In  Cyathophylloids  (Figs.  304-306)  the  corals  are  sometimes  separate 
and  of  a  horn-like  form,  and  sometimes  aggregated  in  large,  rough, 


FIG.  302.  FIQ.  303. 

FIGS.  298-303.— SILURIAN  PROTOZOANS:  298.  Stromatopora  concentrica.  299.  Section  of  same. 
300.  \iew  from  above  (after  Hall).  801.  Receptaculitis  formosus  (after  Worthen).  302.  Dia- 
gram showing  structure  of  Receptaculitis  (after  Nicholson).  303.  Brachiospongia  Rcemerana. 
x  J  (after  Marsh). 

20 


806 


PALEOZOIC  SYSTEM   OF  ROCKS. 


columnar  masses  (Rugosa).  Their  upper  portions  are  cup-shaped ',  and 
the  radiating  lamince  are  very 
distinct.  In  Favositids  (Fig. 
307)  the  hexagonal  parallel  col- 
umns are  divided  somewhat 
minutely  by  horizontal  plates 


FIG.  304. 


FIG.  306. 


FIGS.  304-306.— CYATHOPHYLLOID  CORALS:  304.  Lonsdaleia  floriformis  (after  Nicholson).     305. 
and  b.  Zaphrentis  bilateralis  (after  Hall).    306.  Strombodes  pentagonus  (.after  Hall). 


FIG.  307.  FlG'm 

FIGS.  307-309.— FA  VOSITID  AND  HALYSITII>  COHANS :  307.  Colnmnariaalveolata:  a,  vertical:  b.  cross- 
section  (after  Hall).    308.  Syringopora  verticillata.    309.  Halysites  catenulata  (after  Hall). 


SILURIAN   ANIMALS. 


307 


(Tabulatae)  (Fig.  307,  «),  giving  a  cellular  structure  which  may  be  finer 
or  coarser.  The  Halysitids  (Fig.  309)  seem  to  be  made  up  of  small,  hol- 
low, flattened  columns  with  imperfect  septa,  united  to  form  reticulating 
fluted  plates,  which  on  section  have  the  appearance  of  chains  crossing 
in  all  directions.  These  are  also  minutely  tabulated.  The  Syringopo- 
roids  (Fig.  308)  are  similar  to  the  Halysitids,  except  that  the  hollow 
columns  are  cylindrical  and  connect  with  each  other  only  in  places. 

Some  of  the  more  characteristic  species  of  these  families  are  given 
above  (Figs.  305-309). 

There  are  many  other  forms  than  those  mentioned  above,  but  their 
affinities  are  little  understood,  and  many  are  not  true  corals,  but  Polyzoa 
and  sponges.  Nearly  all  the  corals  of  Silurian,  in  fact,  of  Palaeozoic 
times,  fall  under  two  orders — Rugosa  and  Tabulata.  The  Cyatho- 
phylloids  are  Rugosa,  the  other  families  mentioned  are  Tabulata.  The 
Rugosa  are  character- 
istic of  the  Palaeozoic ; 
the  Tabulata  are  also 
nearly  extinct:  they 
have  only  one  family 
living,  viz.,  the  milli- 
pores.*  The  Rugosa 
differ  from  modern 
star-corals  in  having 
their  radiating  septa 
in  multiples  of  four, 
while  modern  star- 
corals  have  theirs  in 
multiples  of  five  or 
six.  Hence  star-cor- 
als have  been  divided 
into  two  types — a 
Palaeozoic  and  a  Neo- 
zoic —  the  one  four- 
parted  (quadriparti- 
ta),  the  other  six- 
parted  (sexpartita). 
Halysitids  are  charac- 
teristic of  Silurian; 
Favositids,  of  Siluri- 
an and  Devonian; 

and  CvathOT)hvlloids      Fl«9-  SlO-Sia.— LIVING  HTDROZOA.:  310.  Sertularia  pinnata:  a,  nat- 
J  •     J  ural  size;  6.  enlarged.    311.  a  and  b,  Different  Forms  of  Sertula- 

Of  the  PalCBOZOic.  ria.    312.  Plumularia. 


FIG.  310. 


PIG.  311. 


Fio.  312. 


*  Millipores  are  now  shown  to  be  Hydrozoa  (Hydro-corals).     It  is  possible  that 
ae  mav  be  true  of  Tabulata. 


the 


same  may  be  true  of  Tabulata. 


308 


PALAEOZOIC  SYSTEM   OF  ROCKS. 


Hydrozoa. — The  perfect  forms  of  this  class,  viz.,  Medusas,  or  jelly- 
fishes,  are  so  soft  and  perishable  that,  with  one  or  two  exceptions  in 

the  Mesozoic  rocks, 
they  are  not  found  pre- 
served at  all  in  the 
strata  of  any  geological 
period.  They  may  or 
may  not  have  existed 
at  this  time ;  probably 
they  did  not.  But  the 
larval  form  of  most,  if 
not  all,  Medusa3  is  a 
compound  polypoid  an- 
imal, forming  a  minute- 
ly-branching, horny,  or 
coralline  axis.  These 
minutely  -  branching 
axes  are  strung  on  each 
side  with  cells,  in  which 
are  inclosed  little  poly- 
poid animals.  They 
grow  in  still,  quiet  wa- 
ters, and  are  often  mis- 
taken by  the  unscien- 
tific for  sea  -  weed. 
These,  by  their  compo- 
sition, are  well  adapted 
for  preservation,  and  it 
is  this  larval  form, 
therefore,  only  that  we 
might  expect  to  find. 
Figs.  309-311  are  ex- 
amples of  living  forms. 
Now,  in  very  fine 
shales  of  Silurian  age, 
especially  of  Lower  Si- 
lurian and  Cambrian, 
are  found  abundantly 
beautiful  impressions  of 
organism  which  is 


FIG.  313. 


FIG.  314. 


^^     *****" 

v 

FIG.  315. 


an 


FIG.  316. 


FIG.  317. 


313. 


Diplograpl 
typus  (afte 


tus  pristis  (after 


FIGS.  313-317.— GRAPTOLITES 
Nicholson).     314        „"        ,_ 

dymograptus  V-fractns  (after  Hall).  316.  Graptolithus  Logani 
(after  Hall).  317.  Monograptus  priodon:  a,  side  view,  ft, 
back  view;  c,  front  view,  showing  opening  (after  Nicholson). 


Phyllograptus  typus  (after  Hall).    315.  Di- 
•  fter  Har 


most  probably  a  com- 
pound Hydrozoan  al- 
lied to  Sertularia  of  the 
present  day.  They  are 


SILURIAN  ANIMALS. 


309 


called  graptolitzs..  Sometimes  the  cells  are  arranged  on  one  side  of  the 
axis,  sometimes  on  both  sides,  sometimes  the  axis  is  divided.  What- 
ever be  their  affinities,  they  are  of  great  importance,  inasmuch  as  they 
are  entirely  characteristic  of  the  Silurian  age,  and  those  with  cells  on 
both  sides,  of  the  Lower  Silurian  and  Cambrian.  The  twin  graptolites 
(Fig.  315)  are  also  wholly  characteristic  of  Lower  Silurian. 


FIG.  318. 

Fios.  318,  319.— GRAPTOLITES:  318.  Dendrograptus  Hallianus  (after  Hall).    319.  Graptolitea  Clinto- 

nensis  (after  Hall). 

Polyzoa. — There  are  many  kinds  of  compound  coralline  animals, 
probably  allied  to  the  Bryozoa  (sea-mats)  (Fig.  320)  of  our  present  seas, 
found  in  the  Silurian.  The  doubtful 
affinities  of  these  Paleozoic  forms,  and 
the  difficulty  of  separating  them  sharply 
from  certain  forms  of  true  corals  on  the 
one  hand,  and  from  certain  forms  of 
graptolites  on  the  other,  seem  to  require 
their  notice  in  this  connection,  although 
their  affinities  are  probably  molluscoid. 
Two  of  the  Silurian  forms  are  represented 
in  Figs.  321  and  322. 

Eehinoderms. — During  Silurian  times 
the  class  of  Eehinoderms  was  represented 
principally  by  Crinoids.  A  Crinoid  is 
a  stemmed  Echinoderm,  usually  with 
branching  arms.  The  animal  consists  of  a  long  jointed  stalk,  rooted  to 
the  sea-bottom,  and  bearing  atop  a  rounded  or  pear-shaped  body,  cov- 
ered with  calcareous  plates  (calyx),  from  the  margin  of  which  spring  the 
arms,  which  may  be  long  and  profusely  branched,  or  short  and  simple, 
or  absent  altogether.  In  the  middle  of  the  calyx,  between  the  bases  of 
the  arms,  is  placed  the  mouth.  Their  general  structure  and  appear- 
ance will  be  better  understood  by  examination  of  the  following  figures 
(323-325)  of  living  Crinoids. 


FIG.  320.— Living  Polyzoa :  Flustra  trun- 
cata:  o,  natural  size;  6,  enlarged  to 
show  the  cells. 


310 


PALAEOZOIC   SYSTEM   OF  ROCKS. 


At  present,  leaving  out  the  Holothurians,  or  sea-cucumbers,  which, 
having  no  shell,  are  little  apt  to  be  preserved  as  fossils,  the  class  of 


PIG.  321. 


FIG.  322. 


FIGS.  321  and  322.— SILURIAN  POLTZOA:  321.  Fenestella  elegans  (after  Hall).    322.  Alecto  aulopo- 

roides  (after  Hall). 

Echinoderms  may  be  conveniently  divided  into  three  orders,  viz. :  the 
Ecliinoids,  or  sea-urchins ;  the  Asteroids,  or  star-fishes ;  and  the  Cri- 

noids.     The  members  of  the 
first  and  second  orders  are  free 


moving,  while  those  of  the 
third  are  stemmed.  Of  these 
orders  the  Crinoids  are  the 
lowest,  as  proved  not  only  by 
their  simpler  organization, 
but  also  by  the  fact  that  a 
living  Crinoid,  the  Comatula 
(Fig.  325),  is  attached  when 
young,  but  free  when  mature. 
Now,  in  Silurian  times, 
the  stemmed  Echinoderms  are 
very  abundant,  while  the  free 
are  very  rare  :  at  the  present 

FIG.  323.  FIG.  324.  .  J 

FIGS.  323  and  324.-LIVING  CRINOIDS:  323.  Rhizocrinus    time,    On  the  Contrary,  the  1*6- 

verse  is  the  case.  Thus,  in 
the  course  of  time,  the  former 
decreased  until  they  are  now  almost  extinct,  while  the  latter  increased 
until  they  are  now  very  abundant.  If  we  take  the  abundance  of  Echino- 
derms during  geological  times  as  constant,  and  represent  the  course  of 
time  by  the  absciss  A  B  (Fig.  326),  and  the  abundance  by  distance 
from  A  B  to  C  D,  then  the  parallelogram  would  represent  this  fact. 


Lofotensis  (after  Thompson). 
Caput-Medusae. 


324.    Pentacrinus 


SILURIAN  ANIMALS. 


311 


If,  now,  we  draw  the  diagonal,  C  .Z?,  then  the  shaded  triangle  would 
represent  the  stemmed,  and  the  unshaded  the  free,  and  the  diagonal  the 


FIG.  325.— A  Living  Free  Crinoid— Comatula  roeacea,  the  Feather-Star:  a,  free  adult;  b,  fixed  young 

(after  Forbes). 

line  of  decrease  of  the  one  and  increase  of  the  other ;  and  the  whole 
figure  the  general  relations  of  the  two  sub-classes  throughout  time.    In 


____—  PALAEOZOIC  

^Silurian         Devon?       Carlonif? 


NEOZOIC 


STEM  M  ED 

FIG.  326.— Diagram  showing  the  Distribution  in  Time  of  the  Class  of  Echinoderms. 

the  Palaeozoic  the  stemmed  predominate ;  in  the  Mesozoic  the  two  are 
equally  represented ;  in  modern  times  the  free  predominate. 

Stemmed  Echinoderms,  or  Crinoids,  may  be  divided  into  three  fami- 
lies, viz. :  1.  Crinids  ;  2.  Cystids  ;  3.  Blastoids.  Crinids  are  the  typical 
Crinoids,  with  branching  arms,  already  illustrated  from  living  examples 
(Figs.  323-325).  Cystids  (Figs.  327-330)  are  of  a  bladder-like  form 
(hence  the  name),  and  are  either  without  arms,  or  else  have/ew,  short, 
simple  arms  springing  from  near  the  center  of  the  upper  part  of  the 
body,  the  mouth  being  probably  on  one  side.  The  radiated  structure 
in  these  is  imperfect.  Blastoids  (Gr.  /?Aa<rros,  a  bud)  had  a  bud-shaped 
body,  with  five  petalloid  spaces  (ambulacra)  radiating  from  the  top  and 


312 


PALEOZOIC  SYSTEM  OF  ROCKS. 


reaching  half-way  down  the  body  (see  Figs.  523-526,  page  392).     If 
Crinids  are  comparable  to  inverted  Star-fishes  with  many  arms  and  set 


FIG.  331. 


FIG.  332. 


FIGS.  327-332.— SILURIAN  CRINOIDS:  327.  Caryocrinus  ornatus.  328.  Pleurocystitis  squamosus. 
339.  Pseudocrinus— a  cystid  restored  (after  Liitken).  330.  Lepadocrinus  Gebhardii.  331.  Glyp- 
tocrinus  decadactylus  (after  Hall):  «,  specimen  with  arms;  b,  larger  specimens  without  the 
arms.  332.  Ichthyocrinus  sublaevis  (after  Hall). 

upon  a  stalk,  the  Oystids  and  Blastoids  may  be  compared  to  Sea-urchins 
similarly  set.  All  these  families  are  found  in  the  Silurian.  The  Cys- 
tids  pass  away  with  the  Silurian,  and  are  therefore  characteristic  of 
that  age.  The  Blastoids  pass  away  before  the  end  of  the  Carbonifer- 
ous age,  and  are  therefore  characteristic  of  the  Palaeozoic  era,  but  espe- 
cially of  the  Devonian  and  Carboniferous  ages.  The  distribution  of 
the  three  orders  in  time  is  shown  in  diagram  (Fig.  326).  The  Crinids 
continue,  though  in  diminished  numbers,  to  the  present  day ;  but  of 
course  in  very  different  families.  Figures  of  Blastoids  are  given  under 
the  Carboniferous,  where  they  were  far  more  abundant. 


FIG.  335.  FIG.  336.  FIG.  337. 

FIGS.  333-337.— SFLITRIAN  CRINOIDS  AND  ASTEROIDS:  333.  Mariacrimis  nobilissimiis  (after  Hall). 
334.  Homocrinns  scoparius  (after  Hall).  335.  Heterocrinus  simplex  (after  Meek).  336.  Protas- 
ter  Sedgwickii.  337.  Palajaster  Shaefferi  (after  Hall). 

Mollusks — Aceplials  or  Bivalves. — Bivalves  may  be  divided  into  two 
great  sub-classes,  viz.,  Lamellibranchs  (leaf -gills)  and  Bracliiopods  (arm- 
feet).  The  valves  of  Lamellibranchs  are  right  and  left;  those  of 
Brachiopods  are  upper  and  lower,  or  dorsal  and  ventral.  Brachiopods 
are  much  less  highly  organized  than  the  other  sub-class,  and  differ  so 
essentially  in  their  organization  that  some  of  the  best  naturalists  re- 
move them  not  only  from  the  class  of  Acephals,  but  from  the  depart- 
ment of  Mollusca,  and  ally  them  rather  with  the  Worms.  Their  gen- 
eral resemblance  in  external  form  to  bivalves  makes  it  more  convenient 
to  treat  them  under  that  head,  until  the  question  of  their  affinity  is 
more  definitely  settled.  Brachiopods  are  very  abundant  in  the  Silurian. 


314 


PALEOZOIC  SYSTEM  OF  ROCKS. 


General  Description  of  a  Brachiopod.— A  Brachi- 
opod  shell  consists  of  two  valves,  a  dorsal  and  a  ven- 
tral. The  ventral  is  the  larger,  and  usually  projects 
beyond  the  dorsal,  at  the  hinge,  as  a  prominent  beak. 
This  projecting  portion  is  often  perforated  to  give 


FIG.  339.— Rhynchonella  sulcata:  Bide  view,  dorsal  view,  and  showing 
suture. 

passage  to  a  muscular  peduncle,  by  which  the  shell  is 
attached  in  the  living  animal.  The  following  figures 
(Figs.  338-347)  of  Brachiopods,  living  and  extinct, 
will  make  these  points  clear. 

The  viscera  of  a  Brachiopod  fill  but  a  small  space 
in  the  shell,  this 
cavity  being  occu- 
pied     principally 

by  two  long  spiral  arms  (hence  the 

name),  which  probably  subserve  the 


FIG.  338.  —  Lingula 
anatina,  showing 
the  muscular  ped- 
uncle by  which  the 
shell  is  attached. 


FIG.  340. 


FIG.  342. 


FIGS.  340-342.— SHOWING  THE  STRUCTURE  OF  BRACHIOPODS:  340.  Spirifer  striatns  (Carboniferous): 
a,  dorsal  surface;  6,  interior,  showing  the  bony  spirals.  341.  Terebratula  flavescens  (living 
species):  a,  exterior  surface;  b.  showing  bony  structure  for  attachment  of  spiral  arms.  342. 
Spirifer  hysterica  (Carboniferous):  a,  exterior;  b,  showing  bony  spires. 


SILURIAN  ANIMALS. 


315 


functions  of  respiration  and  alimentation.  These  arms  are  attached 
to  a  curious  bony  apparatus,  sometimes  itself  spiral  in  form.  Figs. 
335-337  show  the  internal  structure  described  above. 


FIG.  343.— Diagram  showing  the  General  Relation  in  Time  of  Brachiopods  to  Larnellibranchs. 

In  the  present  seas  the  Lamellibranchs  are  extremely  abundant, 
while  the  Brachiopods  are  nearly  extinct,  being  represented  by  very 
few  species.  In  Silurian  times,  on  the  contrary,  the  very  reverse  is 
the  case,  bivalve  shells  being  represented  mostly  by  Brachiopods. 


FIG.  344. 


FIG.  34(3. 


FIG.  341; 


FIGS.  344-347.— SILURIAN  BRACHTOPODS:  344.  Orthis  Davidsonii.    345.  Orthis  porcata.    346.  Spiri- 
fer  Cumberlandise:  a,  ventral  valve;  b,  dorsal  valve;  c,  suture.    347.  Pentamerus  Knightii. 

Taking  the  number  of  bivalve  species  throughout  geological  times  as 
constant,  then  the  general  relation  of  these  two  sub-classes  to  each  in 
time  may  be  roughly  represented  by  the  following  diagram,  in  which 
the  lower  triangle  represents  Brachiopods,  the  upper  Lamellibranchs, 
and  the  common  diagonal  the  line  of  decrease  of  one  and  increase  of 
the  other. 


316 


PALAEOZOIC  SYSTEM  OF  ROCKS. 


The  abundance  of  individuals  and  the  number  of  species  of  this 
order  in  Silurian  times  are  almost  incredible.  The  accompanying 
figure  srepresent  some  of  the  common  and  characteristic  forms. 

It  is  very  difficult  to  give  any  general  distinctive  mark  of  Silurian 
Brachiopods,  although,  of  course,  the  species  and  even  the  genera  are 
peculiar,  and  may  be  recognized  by  the  paleontologist.  It  may  be  said, 
however,  that  the  straight-hinged  or  square-shouldered  Brachiopods, 
including  the  Spirifer  family,  the  Strophomena  or  Leptena  family,  and 

the  Productus  family,  are  characteristic  of 
the  Palasozoic,  though  not  of  the  Silurian. 
Lamelliforanchs. — We  have  said  that 
Lamellibranchs  are  also  found  in  the  Si- 
lurian, but  not  so  abundantly  as  the  Brach- 
iopods. Lamellibranchs  are  divided  into 


FIG.  349.  FIG.  350.  FIG.  351.  FIG.  352. 

FIGS.  348-352.— SILURIAN  LAMELLIBRANCHS  :  348.  Orthonota  parallela.  349.  Cardiola  interrnpta 
(after  Hall).  350.  Avicula  Trentonensis  (after  Hall).  351.  Ambonychia  bellistriata  (after  Hall). 
352.  Tellenomya  curta  (after  Hall). 

Siphonates  and  Asiphonates,  i.  e.,  those  with  and  those  without  breath- 
ing-siphons behind.     The  Siphonates  are  the  higher.     At  present  the 
Siphonates  are  the  more  abundant — in  Palaeozoic  times  the  Asipho- 
nates.      We   give 
some  figures  above 
(348-352). 

Gasteropods— 
Univalves.—  Land 
and  fresh-water 
Gasteropods  have 
not  been  found  in 
the  Silurian.  If  we 
divide  marine  Gas- 
teropods or  uni- 
valves into  those 
having  beaked 
shells  and  those 
having  smooth- 


FIG.  354. 


FIG.  355. 


FIGS.  353-355.— SILURIAN  GASTEROPODS  :    353.   Plenrotomaria  dryope. 
354.  Pleurotomaria  agave.    355.  Murchisonia  gracilis. 


SILURIAN  AXIMALS. 


317 


mouthed  or  beakless  shells,  the  former  being  carnivorous  and  the  latter 
herbivorous,  then  only  the  smooth-mouthed  or  beakless  shells  have 
been  found  in  the  Silurian.  The  beaked-shelled 
are  usually  regarded  as  the  more  highly-organ- 
ized class.  The  affinities  of  Conularia  (Fig.  359) 
are  little  understood.  They  are  usually  placed 
among  Pteropods. 


FIG.  356. 


FIG.  357. 


FIG.  358. 


FIG.  359. 


FIGS.  356-359.— SILURIAN  GASTEROPODS  AND  PTEROPODS:  356.  Cyrtolites  compressus  (after  Hall). 
357.  Cyrtolites  Trentonensis  (after  Hall).  358.  Cyrtolites  Dyeri  (after  Meek),  359.  Couularia 
Trentonensis  (after  Hall),  a  Pteropod. 

Cephalopods — Chambered  Shells. — These  are  by  far  the  most  highly 
organized  of  Mollusks,  and  the  most  powerful  among  Invertebrates. 
They  are  represented  in  the  present  seas 
by  the  Nautilus,  the  Squids,  and  the  Cut- 
tie-fishes.  If  we  divide  all  known  Cephal- 
opods, living  and  fossil,  into  Dibranchs 
(two  -  gilled)  and  Tetrabranchs  (four- 
gilled),  the  former  being  naked  and  the 
latter  shelled,  then,  at  the  present  time, 
the  Dibranchs,  or  naked,  vastly  predomi- 
nate, there  being  only  a  single  genus  of 

shelled  or  Tetrabranchs  known,  viz.,  the  FIG.  seo.— Pearly  Nautilus  (Nautilus 
Nautilus,  and  of  this  genus  only  three  or 
four  species.     In  the  Silurian  age,  and  for 
many  ages  afterward,  only  the  shelled  existed, 
are  decidedly  the  higher  in  organization. 

Again,  if  we  divide  chambered  shells  into  those  having  simple  septa 
and  central  or  subcentral  tube  or  siphuncle  (Nautiloid),  and  those  hav- 
ing septa  plaited  at  their  junction  with  the  shell  (plaited  suture)  and 
dorsal  tube  (ammonoid),  then  in  the  Silurian  age  the  former  only  were 
represented. 

Again,  if  we  divide  the  Nautiloids  into  straight-shelled  and  coiled- 
shelled,  then  the  straight-chambered  shells  greatly  predominated. 
Straight-chambered  shells  are  called  Orthoceratites  (o/o0os,  straight; 
Kcpas,  horn).  The  Orthoceratites,  therefore,  are  a  very  striking  feat- 
ure of  the  Silurian  age.  They  may  be  defined  as  straight-chambered 


mpilius):  a,  mantle;  6,  its  dorsal 
fold;  c,  hood;  o,  eye;  t,  tentacles; 
f,  funnel. 

The  naked  or  Dibranchs 


318 


PALAEOZOIC  SYSTEM   OF  ROCKS. 


shells,  with  simple  sutures  and  a  central  or  subcentral  siphon-tube 
(siphuncle).     The  siphuncle  of  the  family  was  large  in  proportion  to 


FIG.  361. 


FIG.  362. 


FIG.  361.— Showing  Structure  of  Orthoceratite.  a,  Ormoceras  ;  b,  Actmoceras  ;  c,  Huronia  :  d,  Sec- 
tion of  Siphuncle  of  Huronia. 

FIG.  362.—  Bestoration  of  Orthoceras,  the  shell  being  supposed  to  be  divided  vertically,  and  only  its 
tipper  part  being  shown:  a,  arms;  f,  muscular  tube  ("  funnel "")  by  which  water  is  expelled  from 
the  mantle-chamber;  c,  air-chambers;  s,  siphuncle  (after  Nicholson). 

the  shell,  and  had  often  a  beaded  structure  (Fig.  361,  «,  #,  e,  d).  The 
genera  are  founded  largely  on  the  form  of  this  part. 

They  existed  in  great  numbers,  and  attained  very  great  size.  Speci- 
mens have  been  found  fifteen  feet  long,  and  eight  to  ten  inches  in  diam- 
eter. They  were,  without  doubt,  the  most  powerful  animals  of  that 
time,  the  tyrants  and  scavengers  of  these  early  seas.  We  give,  in  Fig. 
357,  a  restoration  of  the  creature.  They  are  entirely  characteristic  of 
the  Palaeozoic  ;  commencing  in  the  Primordial,  extending  through  into 
the  Carboniferous,  and  passing  out  there.  They  attained  their  maxi- 
mum of  devolopment  in  size  and 'number  in  the  Silurian. 

Although  straight-chambered  shells  (Orthoceratites)  are  most  abun- 
dant and  characteristic,  and  also  the  earliest,  coiled  shells  of  the  same 
tribe  (Nautiloids)  are  also  found,  and  some  of  them  of  considerable 
size,  but  not  until  the  upper  Silurian.  Some  of  these  are  close-coiled 
shells,  true  Nautilus  family ;  others  open- coiled,  and  more  nearly  allied 


SILURIAN  ANIMALS. 


319 


FIG.  363. 


FIG.  367. 

FIGS.  363-367, — SILURIAN  CEPHALOPODS  :  363.  Orthocerae  mednllare  (after  Meek).  364.  Ormoceras 
tenuifilum,  showing  .chambers  and  siphnncle  (after  Hall).  365.  Orthoceras  vertebrale  (after 
Hall).  366.  Orthoceras  multicameratum  (after  Hall).  367.  Orthoceras  Duseri  (after  Hall). 

to  the  straight.  The  gradual  change  from  the  straight  through  the 
open-coiled  to  the  close-coiled  may  be  traced.  Barrande  gives  1,622 
species  of  Cephalopods  in  the  Silurian. 


320 


PALEOZOIC  SYSTEM  OF  ROCKS. 


FIG.  369. 


FIG.  370. 


FIGS.  36«-370.— SILURIAN  CEPHALOPODS:  368.  Trocholites  Ammonias  (after  Hall):  a,  exterior;  6, 
cast,  showing  septa.    369.  Lituites  Graf  toneneis  (Meek  and  Worthen).    370.  Lituites  cornu-anetis. 

Articulates —  Worms. — These  are  fleshy  animals  without  skeletons, 
and  are  therefore  not  preserved.  They  are  known  only  by  their  tracks, 
their  borings,  their  tubes,  and,  more  rarely,  their  teeth.  Nevertheless, 
some  185  species,  according  to  Barrande,  have  been  described  from 
the  Silurian  of  different  countries.  Fig.  371  represents  worm-tubes, 
Fig.  372  worm-tracks,  and  Fig.  373  worm-teeth,  from  the  Silurian. 

Crustacea — TriloUtes. — The  principal  representatives  of  the  articu- 
late department  in  Silurian  times  were  Crustaceans,  but  mostly  of  a 
very  characteristic  order  of  that  class,  now  long  extinct,  viz.,  TriloUtes. 

General  Description. — The  carapace  or  shell  of  these  curious  creat- 
ures was  convex  and  usually  smooth  above,  and  flat  or  concave  below, 
and  divided  transversely,  like  most  Crustacea,  into  a  number  of  movable 
joints.  Several  of  the  front  joints  are  always  consolidated  to  form  a 
head-shield  or  Buckler,  and  sometimes  a  number  of  the  posterior  joints 
are  similarly  consolidated  to  form  a  tail-shield  or  Pygidium.  The 
whole  shell  or  carapace  is  divided  longitudinally,  more  or  less  distinct- 


SILURIAN  ANIMALS. 


321 


ly,  into  three  lobes  (hence  the  name) — a  middle,  a  right,  and  a  left. 
The  viscera  were  contained  in  the  middle  lobe,  the  two  side  lobes 
being  extensions  of  the  shell,  as  seen  in  the  section,  Fig.  375.  #.  Well- 


FIG.  371. 


FIG.  372. 


Fias.  371,  372.— SILURIAN  ANNELIDS  :  371.  Cornulites  serpentarins    (Worm-Tube).    372.  Trail  of  ^ 

an  Annelid  (after  Hall). 

organized  compound  eyes  are  distinctly  seen  in  well-preserved  speci- 
mens on  the  lateral  lobes  of  the  head-shields  (cheeks)  (Fig.  374).  The 
under  side  of  the  animal  has  never  been  distinctly  seen,  and  therefore  the 


v -^ 

C  X  10 
FIG.  373.— Worm-teeth  from  Cincinnati  group,  enlarged  (after  Hinde). 

character  of  the  locomotive  organs  is  not  certainly  known.     But  until 
recently  it  was  believed  that,  like  some  of  the' lower  crustaceans  of  the 


Fio.  374.— Structure  of  the  Eye  of  Trilobites:  a,  Dalmania  plenropteryx;  ft,  eye  slightly  magnified: 
c,  eye  more  highly  magnified;  d,  small  portion  still  more  highly  magnified  (after  Hall). 
21 


322 


PALAEOZOIC  SYSTEM  OF  ROCKS. 


present  day  (Phyllopods),  their  limbs  were  mostly  thin,  flat,  soft,  leaf- 
like  swimmers.  Walcott,  however,  has  recently  shown  that,  in  addition 
to  these  (or  perhaps  instead  of  these),  there  were  also  slender-jointed 
legs  and  spiral  organs  which  were  probably  gills,  as  shown  in  the  section, 
Fig.  375,  b.  Fig.  375,  a,  is  a  complete  restoration  of  the  under  side  by 
Walcott.  On  this  view  it  is  easy  to  see  why  the  under  side  is  never  ex- 
posed ;  for  the  mud,  in  which  they  were  entombed,  would  become  entan- 
gled among  these  leaf -like  swimmers  and  numerous  slender  legs,  and  in 
breaking  the  rock  this  would  determine  the  line  of  fracture  over  the 


FIG.  375. 


FIG.  376. 


FIGS.  375,  376.— SILURIAN  TRFLOBITES:  375.  a,  Eestoration  of  nnder  side  of  calymene;  b,  Section  of 
calymene  senaria  (after  Wolcott).    376.  Calymene  Blumenbachii ;  a.  Same  in  folded  condition. 

smooth  back,  and  leave  the  creature  firmly  attached  by  its  ventral  surface 
to  the  lower  piece.  Not  uncommonly  Trilobites  are  found  folded  up  on 
their  ventral  surface,  so  as  to  bring  head  and  tail  together  and  form  a  kind 
of  ball.  In  such  cases  the  Trilobite  may  be  got  out  of  the  rocky  matrix 
complete ;  but  none  the  less  are  the  feet  completely  hidden  (Fig.  376  a). 


SILURIAN  ANIMALS. 


323 


The  great  number  of  genera  into  which  this  large  order  is  divided 
is  founded  principally  on  the  form  and  sculpturing  of  the  Buckler,  the 
size  and  form  of  the  Pygidium,  the  number  of  the  movable  segments, 
etc.  The  figures  below  and  on  the  next  page  will  give  an  idea  of  some 
of  these  forms. 

It  is  very  interesting  to  observe  that  a  complex  mechanism,  the 
compound  eye  like  that  of  crustaceans  and  insects  of  the  present  day, 
was  already  developed  even  in  the  early  Primordial  times. 

Trilobites  commenced,  as  already  stated,  in  the  earliest  Primordial, 
continued  through  the  whole  Palaeozoic,  and  then  became  extinct  for- 
ever. They  are  therefore  entirely  characteristic  of  the  Palaeozoic.  They 


FIG.  379. 


FIG.  380  a. 


FIG.  380. 


Flos.  377-380  a.— SILURIAN  TRILOBITES  :  377.  Trinncleus  Pongerardi.  378.  Lichas  Boltoni  (after 
Hall).  379.  Acidaspis  crosotus  (after  Meek).  380.  Isotelus  gigas,  reduced  (after  Hall).  380  a. 
Same,  Bide-view. 


324 


PALEOZOIC   SYSTEM   OF  ROCKS. 


reached  their  maximum  of  development,  in  size,  number,  and  variety, 
in  the  Silurian.  Barrande  gives  the  number  of  species  described  in  the 
Silurian  alone  as  1,579.  They  reached  in  some  cases  a  size  equal  to  any 
crustaceans  now  living.  The  Asaphus  (Isotehis)  gigcts-,  from  the  Lower 
Silurian  (Fig.  380),  was  sometimes  twenty  inches  in  length  and  thir- 


FIG.  381.—  Dalmania  limnlurns. 


FIG.  382. — a,  Larva  of  a  Trilobite;  b,  Larva 
of  a  King-Crab  (after  Packard). 


FIG.  383.— Limulus  before  hatching,  Trilobite  Stage:  a,  side  view  ;  *,  dorsal  view  (after  Packard). 

teen  wide.  Parodoxides  (Figs.  289  and  290,  p.  301),  of  the  earliest 
Primordial,  attained  a  length  of  twenty-two  inches.  On  account  of 
their  great  abundance  and  fine  preservation,  their  embryonic  develop- 
ment has  been  carefully  studied  by  Barrande,  who  has  described  and 
figured  twenty  steps  in  the  development  of  some  species.  According 


SILURIAN  ANIMALS. 


325 


to  Agassiz,  we  know  nearly  as  much  of  the  development  of  Trilobites 
as  of  any  living  crustacean. 

Affinities  of  Trilobites. — The  affinities  of  this  very  distinct  order  are 
imperfectly  understood.  Crustaceans  are  divided  into  two  sub- classes,  a 
higher,  Malacostraca  (mollusk-shelled  or  calcareous-shelled),  and  a  lower, 
Entomostraca  (insect-shelled).  Now,  Trilobites,  though  belonging  to  the 
lower  division,  or  Entomostraca,  occupy  a  position  near  the  confines  of 
the  two  divisions.  More  definitely,  they  probably  stand  between  the 
Isopods  (tetradecapod  Malacostracans),  on  the  one  hand,  and  the  Phyl- 
lopods  and  Limuloids  (Entomostracans),  on  the  other.  In  general  ap- 
pearance they  certainly  approach  Limuloids  (horseshoe-crabs  or  king- 
crabs),  and  these  seem  to  have  replaced  them  in  the  process  of  evolution. 
They  are  by  no  means  very  low  in  the 
scale  of  crustaceans  ;  their  position  be- 
ing near  the  middle.  The  larvae  of 
crustaceans,  especially  of  Limuloids, 
greatly  resemble  some  forms  of  Tril- 


FIG.  384. 


FIG.  386. 


FIGS.  384-386.— SILURIAN  EURYPTERIDS:  384.  Pterygotus  Anglicns,  viewed  from  the  under  side, 
reduced  in  size,  and  restored:  c  c,  the  feelers  (antennae),  terminating  in  nipping-claws;  o  o, 
eyes;  m  m,  three  pairs  of  jointed  limbs,  with  pointed  extremities;  n  n,  swimming-paddles,  the 
bases  of  which  are  spiny  and  act  as  jaws — Upper  Silurian,  Lanarkshire  (after  Henry  Woodward). 
385.  Enrypterus  remipes,  greatly  reduced.  386.  Same  restored:  a,  dorsal  view;  b,  ventral  view 
(after  Hall). 

obites,  and  especially  the  larvae  of  Trilobites.     From  early  generalized 
forms  somewhat  like  those  represented  by  Figs.  382  and  383  there  have 


PALEOZOIC  SYSTEM  OF  ROCKS. 


been  probably  differentiated,  in  one  direction  the  more  perfect  Trilo- 
bites,  and  in  the  other  the  Limuloids. 

Eurypterids. — In  the  Upper  Silurian  was  introduced  and  continued 
to  exist  along  with  Trilobites,  during  the  rest  of  the  Palaeozoic,  another 
family  of  huge  Entomostracans  probably  in  advance  of  Trilobites  in 
organization,  viz.,  Eurypterids.^  The  family  includes  the  two  genera 
Eurypterus  (broad  wing)  and  Pterygotus  (winged  ear).  Some  of  the 
latter  are  the  largest  crustaceans  known.  The  huge  Japan  crab  (Ina- 
clius  Koempferi))  with  carapace  sixteen  inches  in  diameter,  and  legs 
four  feet  long,  and  the  Moluccas  king-crab  (Limulus  Moluccanus), 
three  feet  long  and  eighteen  inches  across  the  carapace,  are  the  largest 
crustaceans  now  living.  But  the  Eurypterids  were  some  of  them  far 
greater.  The  Pterygotus  Anglicus  (Fig.  384)  was  six  feet  long  and 
one  foot  wide,  and  the  Pterygotus  Gigas  seven  feet  long  and  propor- 
tionately wide.  The  above  figures  represent  some  species  of  these  two 
genera  from  the  American  and  English  rocks. 

Anticipations  of  the  Next  Age. — There  are  some  plants  and  animals 
still  higher  than  those  mentioned  above,  but  they  are  so  rare  that  it  is 

best  to  treat  them  as  anticipations 
of  the  next  age.  The  most  impor- 
tant of  these  may  be  briefly  noted  : 

1.  A   few  very  small   land-plants 
(Ferns    and    Club-Mosses)     have 
been  found  in  the  Middle  Silurian 
of  this   country  and   of   Europe. 

2.  A  few  small  air-breathers  (in- 
sects, Blattidae  and  Scorpions)  have 
been  found  in  the  Upper  Silurian 
— also  of  both  countries.     We  give 
a  figure  of  one  of  these  very  im- 
portant   discoveries    (Fig.    387). 
That  they  were  really  air-breathers 
is  shown  by  the  spiracles  or  breath- 
ing-pores, a.    3.  A  few  small,  curi- 
ously-formed  fishes,   of  very  low 
organization,  somewhat  similar  to 
some  (Pteraspis)  in  the  Lower  De- 
vonian, have  recently  been  found 
as  low  as  the  Clinton  group  (lower 
part  of  the  Upper  Silurian).    Such 

FIG.  387.—  Paiseopternus— a  Fossil  Scorpion  from  anticipations    are    in    accordance 

Upper  Silurian  of  Scotland  (.after  Peach).  •  i    A      i  i        j  a.-         j  / 

with  the  law  already  mentioned  (p. 

280),  that  the  characteristics  of  an  age  often  commence  in  the  preced- 
ing age.  It  is  better,  however,  to  treat  of  these  classes  in  connection 


DEVONIAN  SYSTEM  AND   AGE   OF  FISHES. 


327 


with  the  age  in  which  they  culminate,  or  at  least  become  a  striking 
feature. 

The  Silurian,  was,  therefore,  essentially  an  age  of  Invertebrates.  In 
number,  size,  and  variety,  these  have  scarcely  been  surpassed  in  any 
subsequent  period.  The  most  characteristic  orders  were :  Among 
plants,  Fucoids ;  among  animals,  Cyathophylloid  and  Tabulate  Corals, 
Graptolites,  Cystidean  Crinoids,  Square-shouldered  Brachiopods,  Beak- 
less  Gasteropods,  Orthoceratites,  and  Trilobites.  Orthoceratites  and 
Trilobites  were  the  highest  animals  of  the  age,  and  the  former  were  the 
rulers  and  scavengers  of  these  early  seas.  We  give  below  a  table  show- 
ing, according  to  Barrande,  the  number  of  Silurian  species  described 
up  to  1872 : 


Sponges  and  other  Protozoans ...  153 

Corals 718 

Echinoderms 588 

Worms 185 

Trilobites 1,579 

Other  Crustaceans 848 

Bryozoans 478 


Brachiopods 1,567 

Lamellibranchs 1,086 

Heteropods  )   ^  890 
Pteropods    ) 

Gasteropods 1,806 

Cephalopods 1,622 

Fishes..  40 


Which,  with  four  of  uncertain  relations,  make  10,074  species. 

SECTION  2. — DEVONIAN  SYSTEM  AND  AGE  OF  FISHES. 

The  name  Devonian  was  given  to  these  rocks  by  Murchison  and 
Sedgwick,  because  in  Devonshire  the  system  occurs  well  developed,  and 
abounds  in  fossils.  In  England  the  system  is  usually  unconformable 
with  the  underlying  Silurian,  and  sometimes  with  the  overlying  Car- 
boniferous, as  in  Fig.  388.  But  in  the  Eastern  United  States,  as 
already  stated,  the  Palaeozoics  are  .conformable  throughout  (Fig.  264). 


d 

FIG.  388.— s,  Silurian;  d,  Devonian;  c,  Carboniferous  (after  Phillips). 

Area  in  United  States. — The  area  over  which  the  Devonian  appears 
as  a  country  rock  in  the  Eastern  United  States  is  shown  in  map,  page  291. 
It  borders  generally  the  Silurian  on  the  south  and  southwest,  extending 
with  it  far  southward  in  the  middle  region,  viz.,  in  Indiana,  Western 
Ohio,  and  Kentucky.  In  the  Basin  Range  region,  especially  about 
White  Pine,  Nevada,  Devonian  is  known  to  exist,  but  the  limits  of 
these  areas  are  too  imperfectly  known  to  be  described. 

Physical  Geography. — In  the  eastern  portion  of  the  United  States 
the  land  of  the  Devonian  age  was  approximately  that  of  the  Silurian 
age  already  described,  increased  by  the  addition  of  the  Silurian  area, 


328 


PALAEOZOIC   SYSTEM   OF  ROCKS. 


which  Silurian  was  of  course  so  much  marginal  sea-bottom  exposed  by 
upheaval  during  and  at  the  end  of  Silurian  times.  There  was  also  a 
large  island  in  the  Devonian  seas  in  the  region  about  Cincinnati,  viz., 
the  Silurian  area,  situated  there  (see  map,  p.  291).  In  the  Plateau 
region  there  was  a  large  extent  of  land  in  later  Silurian  and  Devonian 
times,  as  shown  by  the  absence  of  strata  of  these  times  in  the  Grand 
Canon  section.  At  the  end  of  Devonian  times  the  Devonian  area  was 
added  to  the  existing  land,  and  the  continental  mass  was  further  in- 
creased. 

Subdivision  into  Periods. — In  the  United  States  the  following  five 
periods  are  usually  recognized : 

5.  Catskill  period. 
4.  Chemung  period. 
3.  Hamilton  period. 
2.  Corniferous  period. 
1.  Oriskany  period. 

We  shall,  however,  neglect  these  subdivisions  in  our  general  de- 
scription of  the  life  of  the  age. 

Life- System  of  Devonian  Age — Plants. 

It  will  be  remembered  that  during  the  Silurian  age,  except  a  few 
small  vascular  cryptogams,  the  only  plants  found  were  Fucoids.  These 
continued,  though  under  different  species,  in  Devonian  times.  But,  in 
addition  to  these,  were  now  introduced  land-plants  in  considerable 
numbers  and  variety,  and  decided  complexity  of  organization.  They 
included  all  the  orders  of  vascular  cryptogams,  viz.,  Ferns,  Lycopods, 
and  Equisetce  ;  and  also  Conifers  among  gymnospermous  Phsenogams ; 


FIG.  389.— Microscopic  Section  of  the  Silicifled 
Wood  of  a  Conifer  (Sequoia),  cat  in  the 
long  direction  of  the  fibers.  Post-tertiary  ? 
Colorado  (after  Nicholson). 


FIG.  390.— Microscopic  Section  of  tho  Wood  of 
the  Common  Larch  (Abies  larix),  cut  in  the 
lonfj  direction  of  the  fibers.  In  both  the 
fresh  and  the  fossil  wood  (Fig.  389)  are  seen 
the  disks  characteristic  of  coniferous  wood 
(after  Nicholson). 


and  by  their  great  size  and  numbers  probably  formed  for  the  first  time 
in  the  history  of  the  earth  a  true  forest  vegetation. 


LIFE-SYSTEM   OF  DEVONIAN   AGE— PLANTS.  329 

The  Ferns  were  represented  by  several  genera,  such  as  Cyclopteris 
and  Neuropteris ;  the  Lycopods  (club-mosses)  not  only  by  the  Psilophy- 
ton,  which  had  been  already  introduced  in  the  uppermost  Silurian,  but 
also  now  by  gigantic  Lepidodendrids  and  Sigillarids,  and  the  Equi- 
setae  by  Calamites  and  Asterophyllites.  The  Conifers  were  represented 
by  the  genus  Protaxites,  allied  to  the  yew  (Taxus).  They  are  known 
to  be  conifers  by  their  concentric  rings  of  growth  and  gymnospermous 
tissue,  i.  e.,  the  elliptic  disk-like  markings  on  the  walls  of  the  wood- 
cells  on  longitudinal  section  (Figs.  389  and  390),  and  the  entire  absence 
on  cross-section  of  the  visible  pores  so  character- 
istic of  dycolytedonous  Exogens  (Fig.  391). 
Some  of  these  conifers  have  been  found  by  Daw- 
son  eighteen  inches,  and  one  three  feet,  in  diam- 
eter. There  have  been  fifty  species  of  land- 
plants  of  these  various  orders  found  by  Daw-  FIG.  391.— Pine-wood,  cross- 
son  in  the  Devonian  of  Kova  Scotia  alone.  In 
Figs.  392-402  we  give  the  most  characteristic  Devonian  land-plants. 

General  Remarks  on  Devonian  Land-Plants. — We  will  not  at  present 
discuss  the  affinities  of  these  plants,  and  their  relations  to  evolution, 
because  they  are  similar  to  those  found  in  the  coal,  where  they  exist 
in  far  greater  variety  and  abundance,  and  the  subject  will  be  discussed 
under  that  head.  There  are,  however,  some  thoughts  suggested  by 
the  first  appearance  of  highly-organized  plants  which  ought  not  to  be 
omitted : 

1.  The  ringed  structure  of  Devonian  conifers  shows  that,  at  that 
time,  there  was  a  growing  season  and  a  season  of  rest,  and  therefore, 
probably,  a  warm  and  a  cold  season.    In  one  trunk  the  number  of  rings 
counted  was  150,  indicating  a  considerable  age. 

2.  What  were  the  precursors  of  this  highly-organized  forest  vegeta- 
tion?   That  there  were  precursors,  from  which  these  were  derived, 
there  can  be  no  doubt,  for  we  have  already  found  them  in  the  Upper 
Silurian  ;  but  that  the  steps  of  evolution  were  just  at  this  point  some- 
ivhat  rapid,  seems  also  certain.     It  is  impossible  to  account  for  this 
comparatively  sudden  appearance  of  so  highly-organized  a  vegetation 
by  evolution,  unless  we  admit  that  there  have  been  periods  of  rapid 
evolution,  as  explained  on  page  302.     When  all  the  conditions  are 
favorable  for  a  great  advance,  the  advance  takes  place  at  once,  i.  e., 
with  great  comparative  rapidity. 

3.  We  have  seen  that  the  coal  vegetation  is  to  a  large  extent  an- 
ticipated in  the  Devonian.     So,  also,  to  some  extent,  were  the  condi- 
tions necessary  to  the  preservation  of  this  vegetation  and  the  formation 
of  coal.     In  the  Devonian,  for  the  first  time,  we  find  dark  bands  be- 
tween the  strata,  impregnated  with  carbonaceous  matter.     We  find, 
also,  thin  seams  of  coal,  with  under-clays  filled  with  ramifying  rootlets, 


PALAEOZOIC  SYSTEM  OF  ROCKS. 


FIG.  397. 

FIGS.  392-399.— DEVONIAN  PLANTS  (after  Dawson):  392.  Psilophyton  princeps,  restored.  393.  a, 
Lepidodendron  Gaspianum;  b,  same  enlarged.  394.  a,  Asterophillites  latifolia:  b  fruit  of  same. 
395.  Cyclopteris  obtusa— a  Fern.  396.  Neuropteris  polymorpha.  a  Fern.  397.  Cyclopteris  Jack- 
soni,  a  Fern.  398.  Dadoxylon  Ouangondianum,  a  Conifer:  a,  Pith  ;  b,  Pith-sheath  :  c,  Wood. 
399.  Sections  of  same:  x,  Longitudinal ;  y,  Transverse,  enlarged— z,  greatly  magnified  show- 
ing disk-like  markings. 


DEVONIAN  ANIMALS. 


331 


Fro.  400. 


FIG.  401. 


FIG.  402. 


FIGS.  400-402.— DEVONIAN  PLANTS  (after  Dawson):  400.  Cardiocarpum  Baileyi,  a  Fruit.    401.  An- 
thophyllites  Devonicus.    402.  Cordaites  Robbii,  a  Group  of  Leaves. 

such  as  we  shall  find  in  the  coal ;  in  other  words,  we  find  ancient  dirt- 
beds,  fossil  forest-grounds,  and  fossil  peat-bogs.    All  the  phenomena  of 


FIG.  405. 


FIG.  406. 


FIGS.  403-406.— DEVONIAN  CORALS:  403.  Acervularia  Davidson!  (after  Hall).     404.  Djphyphyllum 
Archiaci.    405.  Zaphrentis  Wortheni  (after  Meek).    406.  Favosites  hemispherica. 


332 


PALAEOZOIC   SYSTEM   OF  ROCKS. 


the  coal-measures,  therefore,  are  here  found,  though  imperfectly  devel- 
oped, and  the  coal  not  workable.  The  Carboniferous  day  is  already 
dawning. 

Animals. 

In  accordance  with  our  prescribed  plan,  all  we  can  do  in  describing 
Devonian  animals  is  to  touch  prominent  points — to  notice  what  is  going 
out,  what  is  coming  in,  some  few  characteristic  forms,  and  to  dwell 
only  on  what  bears  on  evolution. 

Radiates. — Among  corals,  the  chain-corals  (Halysitids)  have  disap- 
peared ;  the  other  orders  continue  under  different  species  (Figs.  403- 
406).  Among  Hydrozoa,  the  Graptolites  are  gone ;  among  Crinoids, 
the  Cyst  ids  are  gone,  but  in  their  place  the  Blastoids  (bud-like),  those 
curious  armless  crinoids,  with  petalloid  markings  already  spoken  of  as 
rare  in  the  Silurian,  become  more  abundant.  The  Grinids,  or  plumose- 
armed  crinoids,  continue  undiminished.  The  Blastoids,  however,  are 
still  more  characteristic  of  the  Carboniferous.  We  therefore  defer  their 
illustration  to  that  period. 

BracMopods. — Brachiopods  are  still  very  abundant,  and  still  many 
of  them  of  the  characteristic  Palaeozoic,  square-shouldered  type.  Among 


FIG.  409.  FIG.  410. 

FIGS.  407-410.-DEVONIAN  BRACHIOPODS:  407.  Spirifer  fornacula  (aftfArnM^e^.a"d.  W°rth*n'>:  <f» 
Ventral  valve;  b,  Suture.  408.  Spirifer  perextensus  (after  Meek).  409.  Orthis  Livia:  a,  Dorsal; 
ft,  Side  view.  410.  Strophomena  rhomboidalis. 

spirifers,  the  long-winged  species  (Fig.  409)   are  very  abundant  and 
characteristic.     We  give  a  few  figures  of  Devonian  bivalves,  both 


DEVONIAN  ANIMALS 


333 


brachiopods  and  lamellibranchs,  and  a  few  univalves.    (It  is  worthy  of 
remark  that  many  of  these  univalves  &TG  fresh-water  species.  J 

Cephalopods. — The  characteristic  Palaeozoic  Cephalopods,  or  Ortlio- 
ceratites,  continue,  but  in  greatly-diminished  numbers  and  size ;  but  the 


FIG.  415. 


FIG.  418. 


FIG.  417. 


FIGS.  411-418.— DEVONIAN  LAMELLIBRANCHS  AND  GASTEROPODS:  411.  Conocardium  trigonale  (after 
Logan).  41&  Aviculopecten  parilis  (after  Meek).  413.  Ctenopistha  antiqua  (after  Meek).  414. 
Lucina  Ohioensis  (after  Meek).  415.  Spirorbis  omphalodes,  enlarged.  416.  Spirorbis  Arkanen- 
sis.  417.  Orthoneina  Newberryi  (after  Meek).  418.  Bellerophon  Newberryi  (after  Meek). 


Goniatites,  a  coiled-chambered  shell,  which  seems  to  be  the  beginning 
of  the  Ammonite  family,  are  introduced  first  here.  This  family,  as 
already  explained,  is  distinguished  by 
the  complexity  of  the  junction  of  the 
septa  and  the  shell  (suture),  and  by 
the  dorsal  position  of  the  siphuncle. 
In  the  Goniatites  the  sutures  are  not 
yet  very  complex.  They  are  only 
zigzag.  This  is  shown  in  the  fig- 
ure. 

Crustacea. — The  very  characteris- 
tic Palaeozoic  order  TriloMtes  is  still 
abundantly  represented,  although  it 
has  already  passed  its  prime,  and  is 
diminishing  in  number  and  size  of 
species.  The  Euryptends  introduced 
in  the  Upper  Silurian  maintain  their  place  through  the  Devonian. 


FIG.  419.— Goniatites  lamellosus  (after 
Pictet). 


334 


PALEOZOIC   SYSTEM   OF  ROCKS. 


FIG.  420. 


FIG.  421. 


FIG.  422.— Wing  of  Platephemera  an- 
tiqua,  Devonian,  America  (after 
Dawson). 


FIGS.  420  and  421. — DEVONIAN  TRILOBITES:  420.  Dalmania  punctata,  Europe.    421.  Phacops  lati- 

frons,  Europe. 

Insects. — We  have  already  seen  (page  326)  that  a  very  few  insects 
(cockroaches  and  scorpions)  have  been  found  in  the  Upper  Silurian. 

We  treated  these  as  anticipations!  In  the 
Devonian,  for  the  first  time,  they  become 
somewhat  abundant ;  and,  as  was  to  be 
expected,  are  found  in  connection  with 
the  abundant  land  vegetation  of  that  time 
(Fig.  422). 

The  Devonian,  and,  indeed,  all  the 
Palaeozoic  hexapod  insects,  belong  to  one 
family,  which  has  been  called  by  Scud- 
der  Palgeodictyoptera  (old  netted- winged), 

a  generalized  type  connecting  the  Neuropters  and  the  Orthopters.  A 
chirping  organ  is  believed  to  have  been  found  in  some.  If  so,  it  implies 
also  an  organ  of  hearing  in  these  early  insects. 

(Fishes. — The  grand  characteristic  of  the  Devonian  is  the  introduc- 
tion here  of  a  new  dominant  class — Fishes — and  of  a  new  department, 
and  that  the  highest,  to  which  man  himself  belongs — the  Vertebrates) 
This  is,  indeed,  a  great  step  in  the  progress  of  life.  It  is  necessary, 
therefore,  to  treat  these  somewhat  fully. 

Commencing  far  back  in  the  Upper  Silurian,  few  in  number,  small 
in  size,  and  of  strange  unfishlike  forms,  with  the  opening  of  the  De- 
vonian fishes  greatly  increased  in  size  and  number,  until  the  waters 
fairly  swarmed  with  them.  Never  since  have  fishes  apparently  been 
more  abundant,  of  greater  size,  or  better  armed  for  offense,  and  espe- 
cially for  defense.  And  yet  all  the  species,  genera,  and  even  families 
then  existent,  are  now  extinct^  Not  only  so,  but  typical  fishes — Tele- 


DEVONIAN  ANIMALS. 


335 


osts — did  not  then  exist.     The  Devonian  fishes  were  all  Ganoids  and 
Placoids,  especially  Ganoids. 

We  have  said  some  were  of  great  size.  The  Dinichthys  (Fig.  423)  of 
the  Ohio  Devonian,  according  to  Newberry,  was  at  least  eighteen  feet 
long  and  three  feet  thick.  A 
specimen  of  Titanichthys  recent- 
ly found  was  nearly  six  feet 
across  the  head  (Claypole),  and 
with  orbits  of  eyes  three  inches 

in  diameter.       The  animal  Could      FIG.  423.— Jaws  of  Dinichthys  Terrelli,  x  &  (after 

hardly  have  been  less  than  thirty 

feet  long.     The  Onychodus  (Figs.  424-426)  was  twelve  to  fifteen  feet 

in  length,  and  had  jaws  two  feet  long,  armed  with  teeth  two  inches 


FIG.  424. 


FIG.  425. 


FIG.  426. 


FIGS.  424-426. — ONYCHODUS  SIGMOIDES  (after  Newberry):  424,  Scale,  natural  size ;  425, 
natural  size  ;  426,  a  Row  of  Front  Teeth,  reduced. 


Tooth, 


long.  We  have  said  also  that  they  were  many  of  them  armed,  espe- 
cially for  defense.  All  Ganoids,  but  especially  Devonian  Ganoids,  were 
covered  with  an  impenetrable  coat  of  mail,  composed  of  thick,  closely- 
fitting,  bony,  enameled  scales  or  plates.  We  are  indebted  to  this  fact 
that  their  external  forms  are  often  so  well  preserved ;  for  their  skele- 
tons were  wholly  cartilaginous,  and  therefore  unsuitable  for  preserva- 
tion. The  Placoids,  on  the  other  hand,  had  neither  bony  skeleton  nor 
bony  scales.  We  know  them,  therefore,  only  by  their  teeth  and  by  cer- 
tain spines  supporting  their  fins.  The  Ganoids  are,  therefore, -the  ^nore 
interesting. 

Characteristic  Examples  of  Devonian  Fishes.  —  The  Cephalaspis 
(Fig.  427)  and  Pteraspis  (Fig.  428)  are  among  the  earliest  and  most 
curious  forms.  The  former  was  a  small  fish,  seven  or  eight  inches 
long,  with  a  broad  head,  shaped  somewhat  like  the  head-shield  of  a 
Trilobite,  and  covered  with  bony,  enameled  plates ;  and  body  covered 
with  rhomboidal  ganoid  scales.  In  the  Coccosteus  and  Pterichthys 
(Figs.  429  and  430)  the  large,  close-fitting,  immovable  plates  covered 
not  only  the  head  but  the  anterior  portion  of  the  body.  The  huge 


336  PALEOZOIC  SYSTEM   OF   ROCKS. 


FIG.  427.— Cephalaspis  Lyelli  (after  Nicholson) 


FIG.  428.— Pteraspis  restored  by  Powrie  and  Lankaster  (after  Dawson). 


FIG.  429.— Pterychthys  restored  (after  Traquair). 


FIG.  430. — Coccosteus  decipiens  (after  Owen), 


FIG.  431.— Holoptychius  nobilissimns  (after  Nicholson). 


DEVONIAN  ANIMALS. 


33T 


Dinichthys  (Fig.  423)  and  Titanichthys  were  similarly  plated  on  head 
and  body.     Others,  however,  such  as  the  Osteolepis  (Fig.  432),  the 


FIG.  432. — Osteolepis  (after  Nicholson). 

Iloloptychitis  (Fig.  431),  Diplachanthus  (Fig.  434),  etc.,  had  more  fish- 
like  forms,  and  were  covered  with  movable  ganoid  scales,  either  rhom- 
boidal  or  imbricated. 


FIG.  436. 


FIGS.  433-136.— DEVONIAN  Fianm—Lepidoffanoids:  433.  Glyptolemns  KinairdSi  (after  Nicholson). 
434.  Diplacanthus  gracilis  (after  Nicholson).  Placmds :  435.  Ctenacanthus  vetustus,  Spine  re- 
duced (after  Newberry).  436.  Machaeracanthus  major,  Spine  reduced  (after  Newberry). 

Perhaps  the  most  extraordinary  and  certainly  the  largest  of  all 
Devonian  fishes  belong  to  the  family  of  Dinichthys.  The  peculiar 
structure  of  jaws  and  teeth  is  shown  in  Fig.  423,  taken  from  Newberry. 
Almost  equally  remarkable  is  another  Ohio  fish  described  by  Dr.  New- 
berry,  the  singular  teeth  of  which  are  shown  in  Figs.  425  and  426. 
22 


338 


PALEOZOIC  SYSTEM  OF  KOCKS. 


Of  the  Placoids  we  can  not  give  figures  of  the  forms,  as  these  are  not 
known ;  but  their  teeth  and  enormous  spines  are  found  (Figs.  435, 436). 

Classification  of  Devonian  Ganoids. — As  above  described,  CDevonian 
Ganoids  fall  naturally  into  two  groups — viz.,  Lepido-ganoids  (scale 


FIG.  442. 


FIGS.  437-442.— NEAREST  LIVING  ALLIES  or  DEVONIAN  FISHES:  437.  Lepidosiren.  438.  Ceratodiis 
Fosterii,  x  &  (after  Gunther).  439.  Polypterus.  440.  Lepidosteus  (Gar-Fish).  441.  Amia 
(American  Mnd-fish).  442.  Cestracion  Phillippi  (a  Living  Cestraciont  from  Australia). 


DEVONIAN  ANIMALS. 


339 


Ganoids),  or  true  Ganoids,  and  Placo-ganoids  (plate-ganoids),  or  Placo- 
derms.  The  former  are  covered,  like  modern  Ganoids,  with  bony,  en- 
ameled scales,  which  may  be  close-fitting,  rhomboidal  (Figs.  432-434), 
or  imbricated  (Fig.  431).  The  latter  are  covered  more  or  less  com- 
pletely with  broad,  immovable  plates.])  The  Placoderms  are  entirely 
characteristic  of  the  Devonian  (and  Upper  Silurian),  and  become  extinct 
after  that  time.  The  Lepido-ganoids  have  continued  in  diminishing 
numbers  and  different  species,  genera,  and  families,  to  the  present  day. 
One  family  of  these  is  very  characteristic  of  Devonian — viz.,  Cros- 
sopterygians  (f ringed-limb),  so  called  because  the  limbs  seem  to  come 
out  from  the  body  into  the  fin  like  a  true  leg.  All  the  strangest  and 
largest  forms — such  as  the  Cephalaspis,  the  Coccosteus,  the  Pterych- 
thys,  the  Dinychthys,  and  the  Titanichthys,  are  Placoderms.  They 
were  heavy,  sluggish,  uncouth  animals,  relying  for  safety  rather  upon 
protective  armor  than  upon  swiftness. 

Nearest  Allies  among  Existing  Fishes. — The  Placoderms  have  no 
close  allies  among  living  fishes),  Some  have  imagined  the  sturgeon  to  be 
distantly  allied ;  and  Dr.  Newberry  finds  some  affinities  in  the  Lepi- 
dosiren  with  the  Dinichthys.  They  were  probably  a  generalized  type 
connecting  Ganoids  and  Placoids.  The  Lepido-ganoids,  however,  still 
have  living  congeners,  which  throw  light  upon  their  structure  (Figs. 
437-441).  Among  the  nearest  allies  are  the  Lepidosiren  and  Protop- 
terus  of  South  American  and  African  rivers,  the  Ceratodus  of  Austra- 
lian rivers,  and  the  Polypterus  of  the  Nile.  It  will  be  noted  that  these, 
especially  the  first  two,  have  almost  veritable  legs  instead  of  paired 
fins.  The  Ceratodus  especially  is  a  living  Crossopterygian.  It  is  well 
to  note  also  that  the  Lepido- 
siren is  the  most  reptilian  or 
rather  amphibian  of  all  fishes, 
and  next  in  this  respect  comes 
Ceratodus.  These  two  have  a 
three-chambered  heart  and  a 
tolerably  good  lung  and  nos- 
trils, and  breathe  air  as  well  as 
water,  like  many  amphibians. 
They  also  have  cartilaginous 
skeletons,  like  Devonian  fish- 
es. Less  near  allies  are  found 
in  the  gar-fish  (Lepidosteus) 
and  the  mud-fish  (Amia)  of 
our  Atlantic  and  Gulf  rivers. 
These  also  supplement  their  gill-breathing  with  a  little  air  gulped 
down  into  their  vascular  air-bladder  from  time  to  time. 

The  nearest  congener  of  Devonian  Placoids  is  found  in  the  Cestra- 


FIG.  443.— Dental  Plate  of  Cestracion  Phillippi. 


340  PALAEOZOIC   SYSTEM   OF  ROCKS. 

cion,  or  Port  Jackson  shark  of  Australia  (Fig.  442).  This  is  charac- 
terized not  only  by  the  strong  bony  spine  supporting  the  median  fins, 
but  also  by  the  cobble-stone-pavement  teeth  (Fig.  443) — characteristic 
of  Devonian  Placoids.  The  family  is  called  Cestracionts.  The  Devon- 
ian Placoids  were  all  Cestracionts. 

General  Characteristics  of  Devonian  Fishes. — Leaving  out  some 
low  aberrant  forms,  which  are  so  soft  and  perishable  that  they  are  un- 
likely to  be  preserved,  and  therefore  are  of  little  geological  importance, 
fishes  may  be  conveniently  divided  into  three  orders — viz.,  Teleosts, 
Ganoids,  and  Placoids.  Under  Ganoids  we  include  also  the  Dipnoi 
(Lepidosiren  and  Ceratodus),  because  these,  though  quite  distinct  now, 
run  into  each  other  completely  in  going  backward  in  geological  time : 
(I.)  Now,  of  these  three  orders,  the  Teleosts  (perfect  bone)  are  by  far 
the  most  numerous  at  present ;  so  much  so,  that  the  word  fish  calls  up 
at  once  this  kind.  Under  this  order  come  all  ordinary  or  tyfrical 
fishes,  such  as  the  perch,  the  salmon,  the  cod,  etc.  In  Devonian  times, 
on  the  contrary,  there  were  no  Teleost  fishes.  They  were  all  Ganoids 
and  Placoids.  Ganoids  are  now  nearly  extinct. 

(2.)  Ganoids  of  the  present  day  have  some  of  them  bony  skele- 
tons (Lepidosteus),  but  most  of  them  cartilaginous  skeletons.  All  the 
Devonian  Ganoids  had  cartilaginous  skeletons.  Placoids,  both  now  and 
in  all  times,  had  cartilaginous  skeletons.  Therefore,  all  Devonian 
fishes,  without  exception,  had  cartilaginous  skeletons. 

(3.)  The  position  of  the  mouth  of  Teleosts  is  usually  at  the  end  of 
the  snout,  or  even  often  looking  a  little  upward.  Ganoids  now,  most 
of  them,  have  the  mouth  like  Teleosts,  at  the  end  of  the  snout ;  but 
some  (sturgeon)  have  it  beneath  on  the  ventral  surface.  The  same 
was  true  in  Devonian  times.  The  Lepido-ganoids  had  the  mouth  at 
end  of  the  snout;  but  the  Placo-ganoids  usually  on  the  ventral  surface. 
Placoids  in  all  times  have  the  mouth  beneath.  Therefore,  all  the  De- 
vonian fishes,  except  the  Lepido-ganoids,  or,  we  might  say,  the  most 
characteristic  Devonian  fishes,  have  the  mouth  in  the  ventral  position. 

4.  The  tail-fins  of  fishes  are  mainly  of  two  types,  the  liomocercal  or 
even-lobed  (Fig.  444),  and  the  heterocercal  or  uneven-lobed  (Fig.  445). 
The  one  is  characteristic  of  Teleosts,  the  other  of  sharks  and  some 
other  fishes.  These  differ  not  only  in  shape,  but  still  more  in  struct- 
ure. In  the  former,  the  back-bone  stops  abruptly  in  a  few  large  joints, 
which  send  off  the  rays  to  the  fin  (Fig.  444,  B),  in  the  latter  the  back- 
bone runs  through  the  fin  and  gives  off  rays  in  pairs  above  and  below 
(Fig.  445,  B).  The  former  is  a  non-vertebrated,  the  latter  a  vertebrated, 
tail-fin.  There  is  still  a  third  style  in  which  the  tail-fin  is  vertelrated 
but  not  asymmetric  as  in  Fig.  446,  A  and  B.  This  style  has  been  called 
isocercal  by  Cope.  It  is  probably  the  most  primitive  type.  Now,  in 
living  Ganoids,  the  tail-fin  is  vertebrated,  though  in  some  cases  only 


DEVONIAN   ANIMALS. 


341 


slightly  so;   in  Devonian  Ganoids  the  tail-fins  are  always  distinctly 
vertebrated.     All  Placoids,  both  living  and  extinct,  have  vertebrated 


FIG.  444. — Homocercal   Tail-fin  :  A, 
form;  B,  structure. 


FIG.  445.— Heterocercal  or  Vertebrated  Tail-fin:  A, 
form;  B,  structure. 


tail-fins.  Therefore,  all  Devonian  fishes,  without  exception,  had  verte- 
brated tail-fins — sometimes  asymmetric  (Figs  431, 434),  and  sometimes 
symmetric  (Figs.  432, 433). 

5.  In  all  Teleosts,  and 
in  nearly  all  living  fishes, 
the  paired  fins  (corre- 
sponding to  limbs)  are 
simply  fins.  The  bones  of 
the  limbs  are  buried  in  the 
body.  But  there  is  one 
very  characteristic  Devoni- 
an family  (CrOSSOpterVffi-  FIG.  446.— Vertebrated  bnt  Symmetrical  Fin:  A,  form; 

v  .          i.i,i,.,.  B,  structure. 

ans)  in  which  the  limb  is  a 

lobe  of  the  body  running  through  the  Jin.     The  relation  between  the 

two  styles  of  paired  fins  is  similar  to  that  of  the  two  styles  of  tail- 


FIG.  447. — Head  and  fore  limb  of  a  Ceratodns.  FIG.  448. — Hind  limb  of  same  (after  Gunther). 

fins.     If,  in  the  other  case,  we  had  a  vertebrated  tail-fin,  in  this  we  have 
legged  paired  fins.    This  style  of  paired  fins  is  still  found  in  some  fishes, 


342  PALAEOZOIC   SYSTEM   OF  EOCKS. 

as  the  Ceratodus,  Fig.  438,  and  the  structure  resembling  a  leg  is  shown 

in  Figs.  447  and  448. 

6.  The  teeth  of  many  Devonian  Ganoids  are  fluted  or  channeled  on 

the  outer  surface  near  the  base  (Fig.  449,  a).     On  section  it  is  found 

that  the  inner  surface  next  the  pulp 
is  deeply  folded  (Fig.  449,  b).  This  is 
called  labyrinthine  structure.  It  is 
still  more  marked  in  early  Amphibians, 
and  may  be  regarded  as  an  amphibian 

character. 

?•  Devonian  Placoids  were  all  Ces- 
tracionts,  i.  e.,  they  all  had  cobblestone- 
pavement  teeth,  instead  of  the  lancet-shaped  teeth  characteristic  of 
modern  sharks. 

Devonian  Fishes  were  Generalized  Types. — Teleosts  are  typical 
fishes ;  Ganoids  and  Placoids,  especially  Devonian  Ganoids  and  Pla- 
coids, were  both  connecting  and  embryonic  types— i.  e.,  along  with  their 
distinctive  fish-characters  they  combined  others  which  connect  them 
with  higher  vertebrates,  especially  amphibians,  and  still  others  which 
are  found  in  the  embryos  of  Teleosts.  The  most  important  connecting 
characters  of  Ganoids,  especially  Devonian  Ganoids,  are :  1.  An  ex- 
ternal protective  armor  of  thick,  bony  plates  or  scales,  such  as  were 
possessed  by  early  amphibians,  and  by  many  reptiles  of  the  present  time. 
2.  Large  conical  teeth  channeled  at  the  base,  and  of  labyrinthine 
structure  on  section.  This  structure  was  very  marked  in  early  am- 
phibians. 3".  A  cellular  air-bladder,  freely  supplied  with  blood,  open- 
ing into  the  throat,  and  capable  of  being  used  to  some  extent  as  a  lung. 
We  do  not  know  that  this  was  true  of  Devonian  Ganoids,  but  it  prob- 
ably was,  since  it  is  true  of  all  their  nearest  living  allies,  viz.,  Lepi- 
dosteus,  Polypterus,  Amia,  and  especially  Ceratodus  and  Lepidosiren. 
4.  In  many  cases  paired  fins  which  had  something  like  jointed  legs 
running  through  them.  5.  The  tail-fin  vertebrated  as  in  reptiles. 

Combined  with  these  connecting  characters  are  others  which  are 
distinctly  embryonic — i.  e.,  are  found  now  in  the  embryos  of  Teleosts. 
The  most  conspicuous  of  these  are :  1.  Cartilaginous  condition  of  the 
skeleton,  and  even  the  retention  of  the  fibrous  notochord,  which  pre- 
cedes in  the  embryo  the  segmentation  of  the  vertebral  column.  2.  In 
the  Placoderms,  the  ventral  position  of  the  mouth,  as  in  the  embryo 
of  Teleosts.  3.  The  vertebrated  tail-fin  may  be  regarded  as  a  connect- 
ing character,  since  it  is  possessed  by  nearly  all  amphibians  and  reptiles. 
But  it  may  be  regarded  also  as  an  embryonic  character,  since  the  tail 
of  a  Teleost  passes  successively  through  the  stages  represented  by  Figs. 
444_446,  being  first  isocercal,  then  heterocercal,  and  finally  homocercal. 
It  is  doubtless  both  connecting  and  embryonic. 


DEVONIAN  ANIMALS. 


343 


111  Placoids,  both  living  and  extinct,  there  is  a  similar  combination 
of  connecting  and  embryonic  characters,  but  in  this  case  the  embry- 
onic seem  to  predominate.  We  have  here,  as  before:  1.  The  carti- 
laginous skeleton.  2.  The  ventral  position  of  the  mouth.  But  in  addi- 
tion to  these,  also,  3.  The  absence  of  an  opercle  or  gill-cover,  growing 
backward  and  covering  the  gill-slits.  4.  Perhaps  the  leathery  or  im- 
perfectly-rayed condition  of  the  fins ;  and,  5.  The  ligamentous  instead 
of  bony  attachment  of  the  teeth. 

On  the  other  hand,  the  Placoids,  at  least  those  of  the  present  day, 
have  some  very  high  connecting  characters  in  their  reproduction.  In 
all  Placoids  the  impregnation  is  internal  and  not  external,  as  is  usual 
in  Teleosts;  and  therefore,  instead  of  spawning  a  great  number  of 
small,  unimpregnated  ovules,  they  lay  either  few  large,  well-covered, 
impregnated  eggs,  like  birds  and  reptiles  (skates  and  some  sharks),  or 
else  incubate  their  eggs  within  the  oviduct,  and  bring  forth  their 
young  alive  (ovo- viviparous)  like  some  reptiles.  In  some  cases  there  is 
even  an  attachment  between  the  yolk-sac  of  the  internally-hatched 
young  and  the  oviduct  of  the  mother,  somewhat'  similar  to  that  of  the 
placenta  to  the  uterus  in  the  mammal.  The  young  of  Placoids  also 
have,  at  first,  a  kind  of  external  branchise,  like  those  of  amphibians. 

The  following  schedule  briefly  embodies  these  facts.  It  is  seen 
that  in  the  Ganoids  the  connecting,  in  the  Placoids  embryonic,  characters 
predominate ;  but  that  in  the  Placoids  the  connecting  characters  are 


GANOIDS. 

PLACOIDS. 

!Bony  armor. 
Teeth  labyrinthine. 
Swim-bladder  =  lungs. 
Paired  fins  =  legged. 
Tail-fin  =  vertebrated. 

E.br.vonicjS^-^-- 

Slt^cbrated.         ["i-g. 
Skeleton  =  cartilaginous.    "] 
Mouth  =  ventral. 
Gill-slits  uncovered.              ^  Embryonic. 
Fins  imperfectly  rayed. 
Teeth  imperfectly  attached.  J 

very  high.  The  Lepido-ganoids  of  Devonian  and  Carboniferous  times 
were  far  more  connecting  or  reptilian  than  the  Ganoids  of  the  present 
day.  Hence  these  have  been  called  Sauroids  by  Agassiz  and  Herpetich- 
thyes  by  Huxley : 

Bearing  of  these  Facts  on  the  Question  of  Evolution.— It  is  seen 
above  that  the  Devonian  fishes  combined  certain  high  characters  with 
certain  low  characters.  From  one  point  of  view  they  seem  lower,  from 
another  higher,  than  ordinary  fishes.  There  has  been  some  dispute, 
therefore,  whether  in  the  history  of  fishes  we  find  a  law  of  progress  or 
a  law  of  regress ;  in  other  words,  whether  or  not  it  sustains  a  law  of-  evo- 
lution. The  dispute  is  a  result  of  a  misconception  of  the  nature  of  evo- 
lution. The  most  fundamental  law  of  evolution  is  the  law  of  differ  en- 


344:  PALAEOZOIC  SYSTEM  OF  ROCKS. 

tiation  and  specialization,  and  the  Devonian  fishes  are  an  admirable 
illustration  of  that  law.  The  law  may  be  stated  thus :  The  first  intro- 
duced of  any  class,  order,  or  family,  are  not  typical  examples  of  their 
class,  order,  etc.,  but  connecting  types — i.  e.,  forms  which,  along  with 
their  distinctive  classic,  ordinal,  or  family,  characters,  combine  others 
which  connect  them  with  other  classes,  orders,  etc.  In  the  process  of 
evolution  such  connecting  or  generalized  forms  as  a  common  stem  are 
separated  into  several  specialized  branches.  Thus  the  Devonian  fishes 
were  not  typical  fishes  as  we  now  know  them,  but  gauroids — i.  e.,  along 
with  their  distinctive  fish  characters  they  combined  others  which  closely 
allied  them  with  amphibians  and  reptiles.  (They  were  the  representa- 
tives and  progenitors  of  both  classes  ;  from  this  common  stem  diverged 
two  branches,  viz.,  typical  fishes  on  the  one  hand,  and  amphibians  and 
reptiles  on  the  other!  Such  connecting  links  with  other  classes  or  or- 
ders are  variously  called  connecting  types,  synthetic  types,  combining 
types,  comprehensive  types,  generalized  t}Tpes.  We  shall  usually  call 
them  generalized  types,  and  their  differentiated  outcomes  specialized 
types.  We  shall  find  many  such  in  the  course  of  the  history  of  the 
organic  kingdom. 

Suddenness  of  Appearances. — But  it  is  impossible  to  overlook  the 
apparent  suddenness  of  the  appearance  of  a  new  class — Fishes — and  a 
new  department — Vertebrates — of  the  animal  kingdom.  At  a  certain 
horizon,  and  that  without  break  by  unconformity,  and  therefore  with- 
out notable  loss  of  record,  fishes  appear  in  great  numbers  and  variety. 
It  looks  at  first  as  if  they  came  without  progenitors.  This  apparent 
suddenness,  however,  is  greatly  diminished  by  recent  discoveries. 
Fishes,  few  in  number,  small  in  size,  and  low  in  organization,  have  now 
been  found  far  down  in  the  Upper  Silurian.  The  gap  is  still  great,  but 
will  be  made  less  and  less  by  continued  discovery.  Nevertheless,  in  spite 
of  all  this  it  is  difficult  to  account  for  the  enormous  increase  in  the 
number,  size,  and  variety  of  fishes  at  the  opening  of  the  Devonian  un- 
less we  admit  paroxysms  of  more  rapid  movement  in  evolution — unless 
we  admit  that,  when  the  conditions  are  favorable,  and  the  time  is  ripe 
for  a  certain  change,  it  takes  place  with  exceptional  rapidity,  perhaps 
in  a  few  generations. 

Amphibians  and  reptiles  have  not  yet  been  found  in  the  Devonian. 
Fishes,  therefore,  were  the  highest  and  most  powerful  animals  then 
living.  They  were  the  rulers  of  the  Devonian  seas.  The  previous 
rulers,  therefore — viz.,  Orthoceratites  and  Trilobites,  according  to  a 
necessary  law  in  the  struggle  for  life — diminish  in  number  and  size, 
and  seek  safety  in  a  subordinate  position. 


CA11BONIFEROUS  SYSTEM.  345 

SECTION  3. — CARBONIFEROUS  SYSTEM. — AGE  OF  ACROGENS  AND 

AMPHIBIANS. 

Retrospect. — Before  taking  up  in  detail  this  important  and  interest- 
ing age,  it  will  be  instructive  to  glance  back  over  the  ground  traversed, 
and  draw  some  conclusions. 

If  we  compare,  in  physical  geography^,  the  American  with  the  Eu- 
ropean Continent,  we  find  the  one  marked  by  simplicity  and  the  other 
by  complexity  of  structure.  This  is  true  not  only  of  the  map-outline, 
but  also  of  the  profile-outline,  or  orographic  structure.  Now,  as  history 
furnishes  the  key  to  social  and  political  structure,  so  geology  furnishes 
the  key  to  physical  structure.  The  American  Continent — at  least  in  its 
eastern  part — has  developed  comparatively  steadily  from  the  Laurentian 
nucleus  southward  and  eastward,  and  probably  northward.  We  have 
already  seen  how  the  Silurian  area  was  added  to  the  Laurentian,  and 
the  Devonian  to  the  Silurian.  It  shall  be  our  pleasure,  hereafter,  to 
show  the  continuance  of  this  steady  development  throughout  the  whole 
geological  history.  For  our  knowledge  on  this  interesting  subject  we 
are  indebted  almost  wholly  to  Prof.  Dana. 

In  the  case  of  America,  the  continent  thus  sketched  in  outline  in 
the  earliest  times  has  been  steadily  worked  out  in  detail  throughout  all 
subsequent  time ;  with  some  very  considerable  oscillations,  it  is  true,  de- 
termining unconformability  of  strata,  rapid  changes  of  physical  geog- 
raphy and  climate,  and  therefore  of  species,  thus  marking  the  great 
divisions  of  time,  but  on  the  whole  without  change  of  plan  or  wavering 
of  purpose ;  in  the  case  of  Europe,  on  the  contrary,  geological  history 
consists  of  a  series  of  oscillations  so  great  that  it  amounts  to  a  successive 
making  and  unmaking  of  the  continent. 

Hence,  nearly  all  geological  problems  are  expressed  in  simpler  terms, 
and  are  more  easily  solved,  here  than  there.  Hence,  also,  while  in  Eu- 
rope the  ages  and  periods  are  separated  by  unconformability  of  the 
rock-system,  as  well  as  change  in  the  life-system,  in  America  they  are 
separated  mainly  by  change  in  the  life-system  only. 

Subdivisions  of  the  Carboniferous  System  and  Age.— The  Carbonifer- 
ous age  is  subdivided  into  three  periods,  viz.  :  1.  Sub-Carboniferous ; 
2.  Coal-measures,  or  Carboniferous  proper ;  3.  Permian. 

The  sub-Carboniferous  was  the  period  of  preparation ;  the  Coal- 
measures  the  period  of  culmination  ;  the  Permian  the  period  of  decline 
and  transition  to  the  Mesozoic.  The  whole  thickness  of  the  carbon- 
iferous strata  in  Nova  Scotia  is  16,000  feet;  in  South  Wales  it  is  14,000 
feet;  in  Pennsylvania  9,000  feet,  and  in  Lancashire  16,336  feet.* 

The  sub-Carboniferous  consists  mainly  of  marine  formations ;  the 

*  Pawkin?,  Nature,  vol.  xxxviii,  p.  449,  1888. 


346  PALAEOZOIC  SYSTEM   OF   ROCKS. 

Coal-measures  mainly  of  fresh-water  formation — the  former  mainly  of 
limestone,  the  latter  mainly  of  sands  and  clays ;  the  fossils  of  the  for- 
mer are,  therefore,  mainly  marine  animals,  of  the  latter  mainly  fresh- 
water and  land  animals  and  plants,  though  marine  animals  are  also 
found.  In  both  Europe  and  America  the  coal-basins  consisting  of  the 
latter  are  underlaid  by  the  former,  which,  moreover,  outcrop  all  around, 
forming  a  penumbral  margin  to  the  dark  areas  representing  coal-basins 
on  geological  maps  (see  map,  page  291).  Between  these  two,  or,  rather, 
forming  the  lowest  member  of  the  Coal-measures,  there  is,  in  many 
places,  a  thick,  coarse  sandstone,  called  the  millstone  grit. 

After  this  general  contrast,  we  will  now  concentrate  nearly  our 
whole  attention  upon  the  Carboniferous  period  proper ;  because  in  this 
middle  period  culminated  all  the  more  striking  characteristics  of  tile 
age.  In  speaking  of  the  life-system,  however,  we  will  draw  from  both 
sub-Carboniferous  and  Carboniferous  indifferently.  The  Permian  we 
shall  treat  only  as  a  transition  to  the  next  era. 

Carboniferous  Proper — Rock-System  or  Coal- Measures. 

The  Name. — The  Carboniferous  period  is  but  one  of  the  three  peri- 
ods of  this  age.  The  Carboniferous  age  is,  again,  but  one  of  the  three 
ages  of  the  Palaeozoic  era,  while  the  Palaeozoic  era  is  itself  but  one  of 
the  four  great  eras,  exclusive  of  the  present,  of  the  whole  recorded  his- 
tory of  the  earth:  The  Carboniferous  period,  therefore,  is  probably  not 
more  than  one  thirtieth  part  of  that  recorded  history.  Yet,  during  that 
period  were  accumulated,  and  in  the  strata  of  that  period  (Coal-meas- 
ures) are  still  inclosed,  at  least  nine  tenths  of  all  the  ivorlced  coal,  and 
probably  nearly  nine  tenths  of  all  the  workable  coal  in  the  world.  It  is 
essentially  the  coal-bearing  period.  When  we  remember  that  every 
geological  period  has  its  characteristic  fossils,  by  means  of  which  the 
formation  may  be  at  once  recognized  by  the  experienced  eye,  it  is  easy 
to  see  the  importance  of  this  simple  fact  as  a  guide  to  the  prospector. 
It  has  been  estimated  that  the  money,  time,  and  energy,  uselessly  ex- 
pended in  the  State  of  New  York  in  explorations  for  coal,  where  any 
geologist  might  be  sure  there  was  no  coal,  would  suffice  to  make  a  com- 
plete geological  survey  of  the  State  several  times  over  !  The  same  is 
true  of  Great  Britain  and  many  other  countries. 

Thickness  of  Strata. — Although  constituting  so  small  a  portion  of 
the  whole  stratified  crust  of  the  earth,  the  coal-measures  are  in  some 
places  of  enormous  thickness.  In  Nova  Scotia  they  are  13,000  feet ;  in 
South  Wales,  12,000  feet ;  in  Pennsylvania,  4,000  feet ;  in  West  Vir- 
ginia, over  4,500  feet ;  in  Indian  Territory,  8,000  to  10,000  feet.* 

Mode  of  Occurrence  of  Coal. — Such  being  the  thickness  of  the  coal- 

*  American  Geologist,  vol.  vi,  p.  238.     1890. 


ROCK-SYSTEM   OR  COAL-MEASURES. 


347 


measures,  it  is  evident  that  but  a  small  proportion  consists  of  coal.  The 
coal-measures  consist,  in  fact,  of  thick  strata  of  sandstone,  shales,  and 
limes  Lone,  like  other  formations;  but  in  addition  to 
these  are  interstratified  thin  seams  of  coal  and  beds  of  Sl 
iron-ore.  Even  in  the  richest  coal-measures,  the  pro- 
portion  of  coal  to  rock  is  not  more  than  as  1  to  50,  and 
the  proportion  of  iron  is  still  much  smaller.  In  some 
coal-fields,  as,  for  example,  in  the  Appalachian,  mechan- 
ical sediments,  shales,  and  sandstones,  predominate ;  in 
others,  as  in  the  Western  coal-fields,  organic  sediments 
or  limestone  predominate. 

The  five  kinds  of  strata  mentioned  are  repeated  in 
the  same  coal-basin  very  many  times — perhaps  100  or 
more,  as  in  the  accompanying  section ;  but,  in  com- 
paring one  coal-field  with  another,  or  in  the  same  coal- 
field, in  comparing  one  portion  of  the  series  with  an- 
other, there  is  no  regular  order  of  succession  discovera- 
ble. Except  that  immediately  in  contact  with  the 
seam,  and  beneath  it,  there  is  nearly  always  a  thin 
stratum  of  fine  fire-clay.  This  constant  attendant  of  a 
coal-seam  is  called  the  under-day.  Again,  immediate- 
ly above,  and  therefore  forming  the  roof  of  the  opened  Flo"  450  _  Ideal 
seam,  there  is  frequently,  though  not  so  constantly,  a 
shale  which,  being  impregnated  with  carbonaceous 
matter,  is  called  the  black  shale  .or  black  slate.  These 
accompaniments  are,  however,  usually  too  thin  to  ap- 
pear on  sections. 

In  different  portions,  however,  of  the  same  coal-field,  at  the  same 
geological  horizon,  we  are  apt  to  find  the  same  order.  This  is  the 
necessary  result  of  the  continuity  of  the  strata  over  the  whole  basin. 
If  we  represent  coal-basins,  with  their  five  different  kinds  of  strata,  by 
reams  of  variously- colored  paper,  then,  while  the  order  of  succession 
may  be  different  in  the  different  reams,  and  in  the  upper  or  lower  por- 
tion of  the  same  ream,  yet  at  the  same  level  we  find  the  same  order  in 
every  portion  of  the  same  ream.  This  is  a  test  of  a  coal-field  even 
when  separated  by  denudation  into  several  basins.  It  is  also  a  mode 
of  identifying  individual  coal-seams ;  for,  if .  the  strata  be  continuous, 
then  the  seam  will  have  the  same  accompanying  strata  above  and  be- 
low. The  Pittsburg  seam  has  been  thus  identified,  with  great  proba- 
bility, over  an  area  of  14,000  square  miles,  and,  allowing  for  removal 
by  denudation,  over  an  original  area  of  34,000  square  miles.  Rogers 
thinks  the  original  area  may  have  been  90,000  square  miles.*  This 


Section,  showing 
Alternation  or 
Different  Kinds 
of  Strata :  /&*, 
Sandstone:  Sh, 
Shale;  L  Lime- 
stone ;  I,  Iron, 
and  c,  Coal. 


Phillips,  Geology,  p.  217. 


348 


PALAEOZOIC  SYSTEM   OF  ROCKS. 


rule  for  the  identification  of  coal-seams  of  known  value  is  often  of 
practical  importance ;  but  it  must  be  remembered  that  the  strata  of 
coal-measures,  both  the  seams  and  the  accompanying  shale  and  sand- 
stones, like  all  other  strata,  thin  out  on  their  edges  (page  174).  Never- 
theless, there  is  a  most  extraordinary  continuity  in  the  strata  of  the 
coal-measures. 

Plication  and  Denudation. — Coal-bearing  strata,  like  all  other  strata, 
were,  of  course,  originally  horizontal  (page  173)  and  continuous,  but, 
like  other  strata,  they  are  now  found  sometimes  horizontal  and  some- 


FIG.  451.— Section  of  Panther  Creek  Coal-Basin  (after  Ashburner). 

times  dipping  at  all  angles,  and  folded  in  the  most  complex  manner. 
In  the  Appalachian  region,  especially  in  the  anthracite  region  of  North- 
ern Pennsylva- 
nia, the  strata  are 
very  much  dis- 
turbed, and  the 
coal-seams  inter- 
with 
often 


FIG.  452.— Illinois  Coal- Field  (after  Daddow). 


stratified 
them 


are 


nearly  perpendicular  (Fig.  451),  while  in  Illinois  and  Iowa  the  coal- 
strata  are  nearly  or  quite  horizontal  (Fig.  452).  But,  whether  horizon- 
tal, or  gently  folded,  or  strongly  plicated,  in  all  cases  denudation  has 
carried  away  much  of  the  upper  portions,  leaving  them  in  isolated 
patches  as  mountains  or  basins,  as  shown  in  the  map  of  Northern  Penn- 
sylvania (Fig.  454)  and  in  the  section  (Fig.  453). 


FIG.  453.— Section  of  Appalachian  Coal-Field,  Pennsylvania,  showing  Effects  of  Erosion  on  Gently 
Undulating  Strata  (after  Lesley). 

By  means  of  the  rule  for  identifying  seams  given  above,  it  is  often 
easy  to  trace  the  same  seam  from  one  basin  to  another,  or  from  one 
mountain-side  to  another,  with  great  certainty. 


COAL-MEASURES. 


349 


FIG.  454.— ilap  of  Anthracite  Region  of  Pennsylvania  (after  Lesley). 

Faults. — It  is  plain,  from  what  has  been  said  above,  that  there  is 
an  essential  difference  between  a  coal-seam  and  a  metalliferous  vein. 
Coal-seams  are  conformable  with  the  strata,  and  are  therefore  worked 
wholly  between  the  strata.  This  would  be  a  comparatively  easy  matter 
if  it  were  not  for  slips  or  faults  which  often  occur,  and  sometimes  make 
the  working  unprofitable.  In  case  of  a  fault,  it  is  important  to  remem- 
ber the  rule  already  given  on  page  231,  viz.,  that  most  commonly  the 


FIG.  455.— Section  across  Yarrow  Colliery,  showing  the  Law  of  Faults  (after  De  la  Beche). 

strata  on  the  foot-wall  side  of  the  fissure  goes  upward.  In  the  following 
section  of  Yarrow  colliery  it  will  be  seen  that  all  the  slips  follow  this  law. 

Thickness  of  Seams. — Coal-seams  vary  in  thickness  from  a  fraction 
of  an  inch  to  forty  or  fifty  feet.  A  workable  seam  must  be  at  least 
two  feet  thick.  A  pure,  simple  seam  is  seldom  more  than  eight  or 
ten  feet.  Mammoth  seams,  such  as  occur  in  the  anthracite  region  of 
Pennsylvania,  and  in  Southern  France,  are  produced  by  the  running 
together  of  several  seams  by  the  thinning  out  of  the  interstratified  shales 
and  sandstones.  They  are,  therefore,  almost  always  compound  seams, 
i.  e.,  separated  by  thin  partings  of  clay — too  thin  to  form  a  good  roof 
or  floor,  and  therefore  all  worked  together. 

Number  and  Aggregate  Thickness. — In  a  single  coal-field,  we  have 
said,  the  strata,  including  the  coal-seams,  are  repeated  many  times.  In 
the  South  Joggin's  section,  Nova  Scotia,  there  are  eighty-one  coal- 
seams,  though  most  of  these  are  not  workable.  In  North  England  there 
are  twenty  to  thirty  seams  In  South  Wales  there  are  more  than  100 
seams,  seventy  of  which  are  worked.  In  South  Lancashire  there  are 
seventy-five  seams  over  one  foot  thick ;  in  Belgium  100  seams,  and  in 


350  PALEOZOIC   SYSTEM   OF  ROCKS. 

Westphalia  117  seams.  The  aggregate  thickness  of  all  the  seams  in 
Lancashire  is  150  feet ;  in  Pottsville,  Pennsylvania,  113  feet ;  in  Western 
coal-fields,  seventy  feet ;  in  Westphalia,  274  feet ;  in  Mons,  250  feet.* 

The  thickest  and  purest  are  usually  near  the  middle  of  the  series. 
Evidently  the  conditions  favorable  for  the  formation  and  preservation 
of  coal  commenced  gradually,  even  back  in  the  Devonian,  reached  their 
culmination  in  the  middle  Coal-measures,  and  gradually  passed  away. 
This  geological  day  had  its  morning,  its  high  noon,  and  its  evening. 

Coal  Areas  of  the  United  States. — In  no  other  country  are  the  coal- 
fields so  extensive  as  in  the  United  States.  The  principal  coal-fields 
are  shown  on  map  of  Eastern  United  States,  on  page  291. 

1.  Appalachian   Coal-Field.  —  This,  the  greatest  coal-field  in  the 
world,  commences  in  Northern  Pennsylvania,  covers  the  whole  of  West- 
ern Pennsylvania  and  Eastern  Ohio,  a  large  portion  of  West  Virginia 
and  Eastern  Kentucky,  then  passes  southward  through  East  Tennessee, 
touches  the  northwest  corner  of  Georgia,  and  ends  in  Middle  Alabama. 
In  general  terms,  it  occupied  the  western  slope  of  the  Appalachian 
from  the  confines  of  New  York  to  Middle  Alabama.    Its  area  is  at  least 
60,000  square  miles. 

2.  Central  Coal-Field. — This  covers  the  larger  portion  of  Illinois, 
the  southwest  portion  of  Indiana,  and  the  western  portion  of  Kentucky. 
Its  area  is  about  47,000  square  miles. 

3.  Western  Coal-Field. — This  covers  the  southern  portion  of  Iowa, 
the  northern  and  western  portion  of  Missouri,  the  eastern  portion  of 
Kansas,  and  then  passes  southward  through  Arkansas,  Indian  Terri- 
tory, and  into  Texas.     Its  area  is  estimated  at  78,000  square  miles. 
These  two  coal-fields  are  seen  to  be  connected  by  sub- Carboniferous. 
They  are  probably  one  immense  field  separated  by  erosion. 

4.  Michigan  Coal-Field. — In  the  very  center  of  the  State  of  Michi- 
gan there  is  another  coal-field  occupying  an  area  of  6,700  square  miles. 

5.  Rhode  Island  Coal-Field. — A  small  patch  of  500  square  miles' 
area  is  found  in  Rhode  Island,  extending  a  little  into  Massachusetts. 

6.  Nova  Scotia  and  New  Brunswick. — This  is  a  large  area  on  both 
sides  of  the  Bay  of  Fundy.     It  is  estimated  at  18,000  square  miles. 

The  following  table  gives  approximately  the  areas  of  American 
coal-fields  of  the  Carboniferous  age  : 

Appalachian 60,000 

Central 47,000 

Western 73,000 

Michigan 6,700 

Rhode  Island 500 

192,200 
Nova  Scotia 18,000 

210,000 

*  Nature,  vol.  xlii,  p.  322,  1890. 


COAL-MEASURES. 


351 


Of  the  190,000  square  miles'  coal-area  of  this  age  in  the  United 
States,  120,000  square  miles  is  estimated  as  workable. 

Extra-Carboniferous  Coal. — All  the  fields  mentioned  above  belong 
to  the  Carboniferous  age.  But,  besides  these,  the  United  States  is  very 
rich  in  coal  of  other  periods.  Probably  50,000  square  miles  might  be 
added  from  strata  of  later  times,  making  in  all  170,000  square  miles  of 
workable  coal.  But  of  these  latter  fields  we  will  speak  in  their  proper 
places. 

Coal-Areas  of  Different  Countries  compared.— The  following  table, 
taken  principally  from  Dana,  exhibits  the  comparative  coal-areas  of  the 
principal  coal-producing  countries  of  the  world : 

United  States 120,000  to  150,000  square  miles. 

British  America 18,000 

Great  Britain 12,000 

Spain 4,000 

France 2,000 

Germany 1,800 

Belgium 618 

Europe,  estimated 100,000 

Eecently  enormous  areas  of  coal  have  been  found  in  China,  much 
of  which  belongs  to  this  age. 

Relative  Production  of  Coal. — But  if  the  extent  of  coal-area  repre- 
sents approximately  the  amount  of  wealth  of  this  kind  present  in  the 
strata,  the  production  of  coal  represents  how  much  of  this  wealth  is 
active  capital ;  it  represents  the  development  of  those  industries  de- 
pendent on  coal.  The  following  table  is  compiled  from  the  best  sources 
at  hand  : 


ANNUAL  COAL-PRODUCTION   IN 
MILLIONS  OF  TONS. 

1846. 

1864. 

1874. 

1884. 

Great  Britain              

31  "5 

90 

125 

160 

United  States  

4-6 

22 

50 

106 

46 

70 

France                        .  . 

4«1 

10 

17 

20 

Belgium  ... 

4*9 

10 

15 

18 

World  

406 

Inspection  of  the  table  shows  that  in  the  principal  coal-producing 
countries  there  is  a  rapid  increase  of  production.  It  is  believed  that,  if 
the  same  rate  of  increase  continues,  the  annual  production  of  Great 
Britain  will  be  in  thirty  years  250,000,000  tons,  and  the  whole  work- 
able coal  will  be  exhausted  in  110  years.*  As  might  be  expected, 
therefore,  British  statesmen  and  scientists  are  casting  about  with  much 
anxiety  for  means  by  which  to  promote  the  more  economic  use  of  coal. 


*  Armstrong,  Nature,  vol.  vii,  p.  291. 


352 


PALEOZOIC  SYSTEM  OF  ROCKS. 


Fortunately,  our  own  country  is  supplied  with  almost  inexhaustible 
stores  of  this  source  of  industrial  prosperity. 

Origin  of  Coal,  and  of  its  Varieties. 

That  coal  is  of  vegetable  origin  is  now  no  longer  doubtful.  "VVe 
will  only  briefly  enumerate  the  evidences  on  which  is  based  the  present 
scientific  unanimity  on  this  subject : 

1.  The  remains  of  an  extinct  vegetation  are  found  in  abundance  in 
immediate  connection  with  coal-seams;  stumps  and  roots  in  the  under- 
day,  and  leaves  and  stems  in  the  black  slate  in  contact  with  the  seam 
and  even  imbedded  in  the  seam  itself.  2.  These  vegetable  remains  are 
not  only  associated  with  the  coal-seam,  but  have  often  themselves  be- 
come coal,  though  still  retaining  their  original  form  and  structure. 
3.  Not  only  these  easily-recognizable  imbedded  vegetable  fragments, 
but  the  imbedding  substance  also,  the  whole  coal-seam,  even  the  most 
structureless  portions,  and  the  hardest  varieties,  such  as  anthracite, 
when  carefully  prepared  in  a  suitable  manner  and  examined  with  the 
microscope,  show  vegetable  structure.  Even  the  ashes  of  coal,  carefully 
examined,  show  vegetable  cells  with  characteristic  markings.  The  fol- 
lowing figures  show  the  results  of  such  examination.  4.  A  perfect  gra- 


FIG.  456.— Section  of  Anthracite:  a.  natural  size; 
b  and  c,  magnified  (after  Bailey). 


FIG.  457. — Vegetable  Structure  in  Coal 
(after  Dawson). 


dation  may  be  traced  from  wood  or  peat,  on  the  one  hand,  through  brown 
coal,  lignite,  bituminous  coal,  to  the  most  structureless  anthracite  and 
graphite,  on  the  other,  showing  that  these  are  all  different  terms  of  the 
same  series.  In  chemical  composition,  too,  the  same  unbroken  series 
may  be  traced.  5.  Lastly,  the  best  and  most  structureless  peat,  by 
hydraulic  pressure,  may  be  made  into  a  substance  having  many  of  the 
qualities  and  uses  of  coal. 

We  may,  with  perhaps  less  confidence,  go  further,  and  say  that  all 


ORIGIN   OF   COAL   AND   ITS  VARIETIES.  353 

the  carbon  and  hydrocarbon  known  to  us  are  probably  of  organic  origin. 
Carbon  probably  existed  at  first  only  as  carbonic  acid,  and  has  been  re- 
duced from  that  condition  only  by  organic  agency. 

Varieties  of  Coal. — The  varieties  of  coal  depend  upon  the  purity, 
upon  the  degree  of  bituminization,  and  upon  the  proportion  of  fixed 
and  volatile  matter. 

Varieties  depending  upon  Purity. — Coal  consists  partly  of  organic 
or  combustible  and  partly  of  inorganic  or  incombustible  matter.  On 
burning  coal,  the  organic,  combustible  matter  is  consumed,  and  passes 
away  in  the  form  of  gas,  while  the  inorganic,  incombustible  is  left  as 
ash.  Now,  the  relative  proportion  of  these  may  vary  to  any  extent. 
We  may  have  a  coal  of  only  one  or  two  per  cent  ash.  We  may  have  a 
coal  of  five,  ten,  fifteen,  twenty  per  cent  ash  ;  the  coal  is  now  becoming 
poor.  We  may  have  a  coal  of  thirty  or  forty  per  cent  ash ;  this  is 
called  bony  coal,  or  shaly  coal ;  it  is  the  valueless  refuse  of  the  mines. 
We  may  have  a  coal  of  fifty  or  sixty  per  cent  ash ;  but  it  now  loses 
the  name  as  well  as  the  ready  combustibility  of  coal,  and  is  called 
coaly  shale.  Finally,  we  may  have  a  coal  of  seventy,  eighty,  ninety, 
ninety-five  per  cent  ash ;  and  thus  it  passes,  by  insensible  degrees, 
through  black  shale  into  perfect  shale.  This  passage  is  often  observed 
in  the  roof  of  a  coal-seam. 

Now,  all  vegetable  tissue  contains  incombustible  matter,  which,  on 
burning,  is  left  as  ash.  The  amount  of  ash  in  vegetable  matter  is  on  an 
average  about  one  to  two  per  cent.  But  as,  in  the  process  of  change 
from  wood  to  coal,  much  of  the  organic  matter  is  lost  (p.  355  et  seq.), 
and  the  relative- amount  of  ash  is  thereby  increased,  we  may  say  that, 
if  a  coal  contains  five  per  cent  or  less  of  ash,  it  is  absolutely  pure — 
i.  e.,  its  ash  comes  wholly  from  the  plants  of  which  it  is  composed ; 
but  if  a  coal  contains  more  than  ten  per  cent  ash,  it  is  probably  impure 
— i.  e.,  mixed  with  mud  at  the  time  of  its  accumulation. 

Varieties  of  Coal  depending  on  the  Degree  of  Bituminization,— 
The  previously-mentioned  varieties  consist  of  pure  and  impure  coals ; 
these  consist  of  perfect  and  imperfect  coals.  We  find  the  vegetable 
matter,  accumulated  in  different  geological  periods,  in  different  stages 
of  that  peculiar  change  called  bituminization.  Brown  coal  and  lignite 
are  examples  of  such  imperfect  coal.  They  are  always  comparatively 
modern. 

Varieties  depending  upon  the  Proportion  of  Fixed  and  Volatile 
Matter. — Coal,  even  when  pure  and  perfectly  bituminized,  consists 
still  of  many  varieties,  having  different  uses,  depending  upon  the  pro- 
portion of  fixed  and  volatile  matters.  These  are  the  true  varieties  of 
coal. 

In  pure  and  perfect  coal,  then,  the  combustible  matter  is  part  fixed 
and  part  volatile.  These  may  be  easily  separated  by  heating  to  red- 
23 


354  PALAEOZOIC  SYSTEM   OF  ROCKS. 

ness  in  a  retort.  By  this  means  the  volatile  matter  is  all  driven  off 
and  may  be  collected  as  tar,  oil,  etc.,  in  condensers,  and  as  permanent 
gases  in  gasometers  ;  and  infixed  matter  is  left  in  the  retort  as  coke. 
Now,  the  proportion  of  these  may  vary  greatly  in  different  coals,  and 
affect  the  uses  to  which  the  coal  is  applied.  For  example,  when  the 
coal  consists  wholly  of  fixed  carbon,  it  is  called  graphite.  This  is  not 
usually  considered  a  variety  of  coal,  because  it  is  not  readily  combusti- 
ble ;  but  it  is  evidently  only  the  last  term  of  the  coal  series.  Its  soft, 
greasy  feel,  its  metallic  luster  and  incombustibility,  and  its  uses  for 
pencils,  as  a  friction-powder,  and  as  a  material  for  crucibles,  are  well 
known. 

When  the  combustible  matter  of  the  coal  contains  ninety  to  ninety- 
five  per  cent  fixed  carbon,  it  is  called  anthracite.  This  is  a  hard,  brill- 
iant variety,  with  conchoidal  fracture  and  high  specific  gravity.  It 
burns  with  almost  no  flame  and  produces  much  heat.  It  is  an  admi- 
rable coal  for  all  household  purposes,  and,  with  hot  blast,  may  be  used 
in  iron-smelting  furnaces. 

If  the  combustible  matter  contains  eighty  to  eighty-five  per  cent 
fixed  carbon,  and  fifteen  to  twenty  per  cent  volatile  matter,  it  becomes 
semi-anthracite,  or  semi-bituminous  coal,  of  various  grades.  These  are 
free-burning,  rapid-burning  coals,  producing  long  flame  and  high  tem- 
perature, because  they  do  not  cake  and  clog.  They  are  admirably 
adapted  for  many  purposes,  but  especially  for  the  rapid  production  of 
steam,  and  therefore  for  locomotive-engines,  and  hence  are  often  called 
steam-coals. 

If  the  volatile  combustible  matter  rises  to  the  proportion  of  thirty 
to  forty  per  cent,  it  becomes  full  bituminous  coals,  which  always  burn 
with  a  strong,  bright  flame,  and  often  cake  and  form  clinkers.  This  is 
perhaps  the  commonest  form  of  coal,  and  may  be  regarded  as  typical 
coal. 

If  the  volatile  matter  approaches  or  exceeds  fifty  per  cent,  then  it 
forms  highly -bituminous  or  fat  or  fusing  coals.  This  variety  is  espe- 
cially adapted  to  the  manufacture  of  gas  and  of  coke. 

Besides  these  there  are  several  varieties  depending  on  physical 
character.  Thus  -cannel  or  parrot  coal  is  a  dense,  dry,  structureless, 
lusterless,  highly-bituminous  variety,  which  breaks  with  a  conchoidal 
fracture.  There  may  be  also  some  varieties  depending  upon  the  kind 
of  plants  of  which  coal  was  made,  but  of  this  we  have  no  certain  evi- 
dence. 

Origin  of  these  Varieties. — There  can  be  little  doubt  that  these, 
the  true  varieties,  are  produced  by  slight  differences  in  the  nature  and 
degree  of  chemical  change  in  the  process  of  bituminization. 

It  will  be  seen  by  the  following  table,  giving  approximate  formulae, 
that  vegetable  matter  and  coal  of  various  grades  have  the  same  general 


ORIGIN  OF  COAL  AND   ITS  VARIETIES. 


355 


composition,  except  that  in  the  latter  case  some  of  the  carbon  and 
much  of  the  hydrogen  and  oxygen  have  passed  away  in  the  process  of 
change  : 


Vegetable  matter,  cellulose 
Bituminous  coal 
Anthracite      " 
Graphite         " 


C4oH80 
C  pure 


The  gradual  loss  of  the  hydrogen  and  oxygen  is  still  better  shown  in 
the  following  table,  in  which  the  constituents  are  given  in  proportion- 
ate weights  instead  of  equivalents,  and  the  carbon  reduced  to  a  con- 
stant quantity  : 


KINDS  OF  VEGETABLE  MATTER  AND  COALS. 

Carbon. 

Hydrogen. 

Oxygen. 

Cellulose  

100-00 

16'66 

133-33 

Wood   

100-00 

12-18 

83'07 

Peat  

100-00 

9-83 

65'67 

Lignite  

100-00 

8'37 

42-42 

Bituminous  coal  . 

100-00 

6-12 

21*23 

Anthracite      "    ... 

100-00 

2'84 

1-74 

Graphite         "    

100-00 

O'OO 

O'OO 

Now,  there  are  two  modes  of  decomposition  to  which  vegetable 
matter  may  be  subjected,  viz. :  1.  In  contact  with  air ;  and,  2.  Out  of 
contact  with  air.  The  first  is  partly  decomposition,  and  partly  oxida- 
tion by  the  air  (eremacausis) ;  the  second  is  wholly  decomposition. 

In  Contact  with  Air. — Under  these  conditions  the  carbon  of  the 
vegetable  matter  unites  with  the  oxygen  of  the  vegetable  matter,  form- 
ing carbonic  acid  (C02) ;  and  the  hydrogen  of  the  vegetable  matter 
unites  with  the  oxygen  of  the  air,  forming  water  (H80).  Further,  it 
is  evident  that,  for  every  equivalent  of  carbon  thus  lost,  there  are  two 
equivalents  of  oxygen  and  four  equivalents  of  hydrogen  lost,  so  as 

always  to  maintain  the  samp  relative  proper-  ___^ 

tion  of  H,  and  0  viz.,  the  proportion  forming 
water  (H20).  The  final  result  of  this  process 
is  pure  carbon.  It  is  very  improbable,  how- 
ever, that  anthracite  or  graphite  is  formed  in 
this  way ;  for  vegetable  matter,  by  aerial  de- 
cay, falls  to  powder.  It  is  very  probable,  however — nay,  almost  certain 
— that  a  peculiar  substance,  pulverulent  and  retaining  vegetable  struct- 
ure in  a  remarkable  degree,  called  mineral  charcoal,  found  very  com- 
monly in  some  stratified  coals  has  been  formed  by  partial  aerial  decay, 
somewhat  as  represented  in  the  table.  Mineral  charcoal  has  a  high 
percentage  of  carbon,  with  very^  little  hydrogen  and  oxygen. 

Out  of  Contact  with  Air.— When  vegetable  matter  is  buried  in 
mud  or  submerged  in  water,  its  elements  react  on  each  other.  Some  of 


Cellulose C8«H6o08o 

Decayed CseHsaOas 

More  decayed.  .Ca^aOa,, 
Final  result C3i 


356  PAL2EOZOIC   SYSTEM   OF  EOCKS. 

the  carbon  unites  with  some  of  the  oxygen,  forming  carbonic  acid 
(C02) ;  some  of  the  carbon  unites  with  some  of  the  hydrogen,  forming 
carbureted  hydrogen  or  marsh-gas  (OH4) ;  and  some  of  the  hydrogen 
unites  with  some  of  the  oxygen,  forming  water  (H20).  These  products 
are  probably  formed  in  all  cases  of  vegetable  decomposition  under  these 
conditions  :  If,  for  example,  we  stir  up  the  mud  at  the  bottom  of  stag- 
nant pools  where  weeds  are  growing,  the  bubbles  which  rise  always 
consist  of  a  mixture  of  002  and  CH4.  In  every  coal-mine  these  same 
gases  are  constantly  given  off ;  the  one  being  the  deadly  choke- damp 
and  the  other  the  terrible  fire-damp  of  the  miners.  Now,  by  varying 
the  relative  amounts  of  these  products,  it  is  easy  to  see  how  all  the 
principal  varieties  of  bituminous  coal  may  be  formed.  I  have  given 
below  the  approximate  composition  of  typical  varieties  of  bituminous 
coal,  and  of  graphite,  and  constructed  formulae  expressing  the  chemical 
change  by  which  they  are  formed  : 


Vegetable  matter  —  cellulose  

CgeHsoOso* 

(    9C02  ) 
Subtract  •<    3CH4  /• 

(  11H2O  ) 

A^ain  vegetable  matter  

C    H    0 

(    VC02 
Subtract  •<    3CII4  V  

(  14H20  ) 
And  there  remain  

n    TT    o    _  j  bituminous  coal 

from 

*  '  ^aeiiao^a       -j         Staff  ordshir 

e 

A^ain  vegetable  matter 

C    H    0 

(  10C02  ) 
Subtract  •<  10CH4  >• 

C    H    0 

1   1  ATI   f)  ( 

• 

And  there  remains  

.  .Gia             —  graphite. 

The  composition  of  vegetable  matter  varies  considerably.  The  com- 
position of  the  varieties  of  coal  is  differently  given  by  different  authori- 
ties. Different  reactions  from  those  above  given  might  be  contrived 
which  would  give  as  good  results.  These  reactions,  therefore,  are  not 
given  as  certainly  the  actual  reactions  which  take  place.  They  are  only 
intended  to  show  the  general  character  of  the  changes  which  take  place 
in  the  formation  of  coal. 

Metamorphic  Coal. — It  is  probable  that  bituminous  coal  is  the  nor- 

*  The  composition  of  wood — timber — is  usually  given  as  about  Ci2H,808.  I  have 
taken  the  formula  of  cellulose  instead,  viz.,  C6H1005;  or,  taking  six  equivalents  for  con- 
venience of  calculation,  C36H6o03o.  I  believe  this  to  be  much  nearer  the  composition  of 
vegetable  matter  of  the  Coal  period  than  is  the  formula  of  hard  wood  like  oak  or  beech. 
All  the  results  may  be  worked  out,  however,  with  equal  ease  by  the  use  of  either  formula 
for  vegetable  matter. 


ORIGIN  OF  COAL  AND  ITS  VARIETIES.  357 

mal  coal  formed  by  the  above  process,  and  that  the  extreme  forms,  an- 
thracite and  graphite,  are  the  result  of  an  after-change  produced  by 
heat.  But  some  geologists  go  further  :  they  believe  that  anthracite  has 
been  changed  by  intense  heat  sufficient  to  vaporize  the  volatile  matters, 
which  then  condense  in  fissures  above,  as  bitumen,  petroleum,  etc. ; 
that,  as  in  art,  when  bituminous  coal  is  subjected  to  heat  out  of  contact 
with  air,  the  fixed  carbon  is  left  as  coke,  the  tarry  and  liquid  matters 
are  condensed  in  purifiers,  and  the  permanent  gases  collected  in  gasom- 
eters ;  so  in  Nature,  when  beds  of  bituminous  coal  are  subjected  to  in- 
tense heat  in  the  interior  of  the  earth,  the  fixed  carbon  is  left  as  anthra- 
cite^ the  tarry  and  liquid  matters  collected  in  fissures,  as  bitumen  and 
petroleum,  while  the  gases  escape  in  burning  springs.  The  process  is 
of  course  slow  and  under  heavy  pressure,  and  therefore  the  residuum  is 
not  spongy  like  coke.  According  to  this  view,  anthracite  and  bitumen 
are  necessary  correlatives. 

There  can  be  no  doubt  that  the  graphitic  and  anthracitic  varieties 
of  coal  are  always  associated  with  folding  and  metamorphism  of  the 
strata :  1.  In  the  universally-folded  and  metamorphic  Laurentian  rocks 
only  graphite  is  found.  2.  In  Pennsylvania,  in  the  strongly-folded  and 
highly-metamorphic  eastern  portion  of  the  field,  the  coal  is  anthracite ; 
while,  as  we  go  westward,  and  the  rocks  are  less  and  less  metamorphic, 
the  coal  is  more  and  more  bituminous,  until,  when  the  rocks  are  hori- 
zontal and  unchanged,  the  coal  is  always  highly  bituminous.  The  same 
has  been  observed  in  Wales :  anthracite  is  always  found  in  metamorphic 
regions,  and  the  coal  is  more  and  more  bituminous  as  the  rocks  are  less 
and  less  metamorphic.  3.  Again,  the  anthracitic  condition  of  coal  may 
be  sometimes  traced  to  the  local  effect  of  trap  or  volcanic  overflows. 
In  a  word,  anthracite  is  mctamorpliic  coal ;  and,  according  to  this  view, 
the  same  heat  which  changed  the  rocks  has  distilled  away  the  volatile 
matters,  which  may  condense  above,  as  bitumen  or  petroleum. 

We  have  given  above  the  common  view.  It  is  partly  true  and  partly 
erroneous.  The  true  view  seems  to  be  as  follows : 

Anthracite  may,  indeed,  be  regarded  as  metamorphic  coal,  but  it  is 
not  probable  that  bitumen  is  its  necessary  correlative ;  it  is  not  probable 
that  the  heat  of  metamorphism  is  sufficient  to  produce  destructive  dis- 
tillation. We  have  already  shown  (page  221)  that  a  moderate  heat  of 
300°  to  400°  Fahr.  in  the  presence  of  water  is  sufficient  to  produce 
metamorphism.  Such  a  degree  of  heat  would,  doubtless,  hasten  the 
process  explained  on  page  356.  The  folding  and  erosion  of  the  rocks, 
and  the  consequent  exposure  of  the  edges  of  the  seams,  would  still 
further  hasten  the  process,  and  bring  about  anthracitism  by  facilitating 
the  escape  of  the  products  of  decomposition.  In  all  coal-mines  C02, 
CH4,  and  H20,  are  eliminated  now ;  only  continue  this  process  long 
enough,  and  anthracite  and,  finally,  graphite  is  the  result.  We  must 


358  PALAEOZOIC  SYSTEM   OF  ROCKS. 

conclude,  then,  that  high  heat  is  not  necessary  to  produce  anthracitism ; 
for,  if  it  is  unnecessary  for  metamorphism  of  rocks,  much  less  is  it  neces- 
sary for  metamorphism  of  coal. 

Plants  of  the  Coal — their  Structure  and  Affinities. 

The  flora  of  the  coal-measures  is  one  of  the  most  abundant  and  per- 
fect of  all  extinct  floras ;  according  to  Ward,  there  are  about  8,660 
known  fossil  species  of  plants,  and  of  these  about  2,000,  or  nearly  one 
fourth,  are  from  the  coal-measures.*  This  flora  is  peculiarly  interest- 
ing to  the  geologist,  not  only  on  account  of  its  relative  abundance,  but 
also  and  chiefly  because,  being  the  first  diversified  and  somewhat 
highly-organized  flora,  it  is  natural  to  suppose  that  the  great  classes 
and  orders  of  the  vegetable  kingdom  commenced  to  diverge  here ;  and 
therefore  it  furnishes  a  key  to  the  evolution  of  land-plants.  We  will, 
therefore,  discuss  the  affinities  of  these  plants  somewhat  fully. 

Where  found. — The  plants  of  the  Coal  are  found  principally :  1.  In 
the  form  of  stools  and  roots  in  their  original  position  in  the  under-day  ; 
2.  Of  leaves,  and  branches,  and  flattened  trunks,  on  the  upper  surface 
of  the  coal-seam,  and  in  the  overlying  shale ;  3.  And,  finally,  in  the 
form  of  logs,  apparently  drift-timber,  in  the  sandstones  above  the  coal- 
seam.  The  black  shale  overlying  the  seam  is  often  full  of  leaves  and 
fronds  of  ferns,  and  of  the  flattened  trunks  of  other  families,  in  the 
most  beautiful  state  of  preservation,  so  that  even  the  finest  venation  of 
the  leaves  is  perfectly  distinct.  In  some  cases  where  the  shale  is  light- 
colored,  so  as  to  contrast  strongly  with  the  jet-black  leaves,  the  effect 
on  first  opening  a  seam  is  very  striking,  and  has  been  compared  to  the 
frescoes  on  the  ceilings  of  Italian  palaces. 

Principal  Orders. — Leaving  out  some  plants  of  doubtful  affinity, 
the  plants  of  the  Coal  may  be  referred  to  five  orders  or  families,  viz., 
Conifers,  Ferns,  Lepidodendrids,  Sigillarids,  and 
Catamites.  It  is  usual  to  refer  these  last  three  to  the 
two  orders  Lycopods  and  Equisetae ;  but  they  are  so 
peculiar,  and  their  affinities  still  so  doubtful,  that  we 
have  preferred  to  treat  them  as  distinct  orders. 

All  these,  as  already  seen,  commenced  in  the  De- 
vonian, as  did  also  the  preservations  of  their  tissues  as 
coal;  but  both  the  vegetation  and  the  conditions 
necessary  for  their  preservation  culminated  in  the 
Coal  period,  and  therefore  we  have  put  off  their  dis- 
cussion until  now.  Contrary  to  our  usual  custom,  we 
wil1  commence  witn  the  highest,  viz. : 
wood;  c,  medullary  j.  Conifers. — A  considerable  number  of  genera  of 

sheath  ;  d,  pith. 

*  Science,  vol.  iv,  p.  340,  1884. 


PLANTS  OF  THE   COAL. 


359 


these  are  known,  but  all  of  them  quite  different  from  living  Conifers. 

They  are  mostly  found :  1.  In  the  form  of  trunks  or  logs  in  the  sand- 
stones above  the  coal-seams  (Fig.  458) ;  2. 
In  the  form  of  leaves,  twigs,  and  leafy 
branches  in  the  roof -shale  (Fig.  459) ;  3.  In 
the  form  of  nut-like  fruits  of  many  kinds, 
also  in  the  roof-shale.  But  they  are  not 
found  as  stumps  and  roots  in  situ  in  the 
under-clay.  From  this  we  conclude  that 


FIG.  459. — Arancarites  gracilis,  re- 
ducedtaf  ter  Dawson). 


FIG.  460.— Section  of  same:  6.  woody  wedges;  c,  pith  and 
pith-rays. 


they  did  not  grow  in  the  coal-swamps,  but  on  the  high  ground  about 
them;  that  their  leaves,  small  branches,  and  fruits  were  washed  down 


FIG.  461. 


FIG.  462. 


FIG.  463. 


FIG.  464. 


FIG.  461-464.— BROAD-LEAVED  CONIFERS.  LIVING  CONGENERS  or  SOME  CoAiy-PLANTs:  461.  Salis- 
buria  (Ginko),  a  branch.  462.  Section  of  fruit  463.  A  leaf,  natural  size.  464.  Phyllocladns, 
a  branch. 

into  the  swamps,  and  their  trunks  were  sometimes  drifted  down  by 
floods  which  overwhelmed  and  buried  the  coal. 

The  trunks  and  woody  branches  are  known  to  be  those  of  Grym- 
nosperms  by  the  characteristic  Gymnospermous  structure  of  the  wood 
(Figs.  389,  390,  page  328),  especially  the  disk-like  markings  on  longi- 


360 


PALAEOZOIC   SYSTEM   OF  ROCKS. 


tudinal  section ;  and  to  be  those  of  Conifers  by  the  existence  of  a  dis- 
tinct bark,  rings  of  growth,  and  pith  (Fig.  458).  But  the  large  size  of 
the  pith  of  some  seems  to  ally  them  with  the  Cycads. 


FIG.  467. 

FIGS.  465-467. — FRUITS  OF  COAL-PLANTS,  PROBABLY  CONIFERS:   465.  Trigonocarpon  (after  New- 
berry).  466.  Cardiocarpon  (after  Newberry  and  Dawson).    467.  Rhabdocarpon  (after  Newberry). 

But  the  leaves,  leafy  branches,  and  fruits  are  still  more  interesting 
and  significant.  By  the  study  of  these,  Carboniferous  Conifers  seem 
to  fall  naturally  into  two  groups,  viz.,  those  with  small,  spine-like 


PLANTS   OF   THE   COAL. 


361 


leaves  (Fig.  459),  reminding  us  of  the  yew  or  the  Araucaria,  and  those 
with  broad,  strap-shaped,  or  tongue-like  leaves,  with  parallel  or  radiated 
venation,  like  that  strange,  broad-leaved  living 
Conifer,  the  Ginko  (Fig.  463).  One  of  the 
commonest  and  most  characteristic  of  this 
group  is  the  Cordaites.  All  parts  of  this 
plant  are  known ;  so  that  we  may  restore  it 
with  some  confidence  (Fig.  468).  We  may 
imagine  a  cylindrical,  branchless  trunk,  some- 
times sixty  to  seventy  feet  high,  clothed  atop 
with  long,  strap-shaped  leaves  like  a  Dracaena, 
and  bearing  clusters  of  nut-like  fruits.  Many 
of  the  fruits  represented  in  the  figures  on  the 
previous  page  are  from  this  tree. 

Affinities  of  Carboniferous  Conifers.— Con- 
ifers of  this  time  were  not  typical  Conifers. 
There  are  no  signs  of  true  cones  in  the  coal. 
All  the  so-called  Conifers  of  that  time  bore 
solitary,  nut-like  fruits.  Now,  Conifers  of  the 
yew  family,  and  the  broad-leaved  Ginko,  are 
the  only  ones  that  now  bear  fruits  which 
might  be  compared  with  these.  These  Coni- 
fers bear  solitary  plum-like  fruits,  with  large,  nut-like  seeds  (Figs. 
461  and  462).  The  Cycads  also  bear  somewhat  similar  fruit.  The  best 
illustration  from  the  yew  family  is  the  California  nutmeg  (Torreya). 
It  bears  a  plum-like  fruit  about  the  size  of  a  large  plum,  with  a  nut- 
like  seed  as  large  as  a  pecan-nut.  It  is,  therefore,  among  the  yew  fam- 
ily and  the  Ginkos  that  we  must  seek  for  allies  of  the  coal  Conifers. 
In  fact,  all  gradations  in  shape  of  the  leaf  may  be  traced  between  the 
Cordaites  (Fig.  469  «,  J)  and  Noggerathia,  of  the  Carboniferous  (c), 
and  Ginkophyllum  of  Permian  (d)  to  Ginko  (e,f)  of  the  Jurassic,  and 


FIG.  468.— Cordaites  (restored  by 
Dawson). 


FIG.  469.— Evolution  of  the  Ginkos:  a  and  ft,  Cordaites,  Carboniferous;  c,  NOggerathia.  Carbonif- 
erous; d,  Ginkophyllum,  Permian;  e,  Ginko  digatata,  OOlite;/,  Ginko  biloba,  living. 

the  present  time.     The  yew  family  and  the  Ginko  may  be  regarded  as 
the  most  generalized  of  Conifers,  connecting  them  closely  with  the 


362 


PALAEOZOIC  SYSTEM  OF  ROCKS. 


Cycads,  on  the  one  hand,  and  the  vascular  Cryptogams  on  the  other. 
Many  writers  ally  the  Cordaites  and  Ndggerathia  with  the  Cycads 
instead  of  the  Conifers.  They  probably  connect  these  two  families  of 
Gymnosperms. 

2.  Ferns. — Ferns  are  the  most  abundant  plants  of  the  Coal  period, 
both  as  to  individuals  and  as  to  variety  of  species.  About  one  third  to 
one  half  of  all  the  known  species  of  coal-plants,  both  in  this  country 
and  in  Europe,  belong  to  this  order.  They  represent  both  ordinary 
forms,  i.  e.,  those  with  creeping  stems,  and  Tree-ferns,  like  those  now 
growing  only  in  warm_  latitudes  (Fig.  470).  They  are  known  to  be 
ferns  by  their  large  complex  fronds  (Fig.  471),  sometimes  six  to  eight 
feet  long ;  by  the  dichotomous  venation  of  their  leaves  (Fig.  475) ; 
and  by  the  position  of  their  organs  of  fructification  (spore-cases)  on  the 
under-surfaces  of  the  leaves  (Figs.  476  and  477).  In  some  localities 
these  spore-cases  are  so  abundant  that  the" coal  seems  to  be  almost 
wholly  made  up  of  them.  The  trunks  of  Tree-ferns  are  known  by  the 
large,  ragged,  ovoid  marks  left  by  the  falling  of  the  fronds  (leaf-scars 
— Figs.  485-487),  and  by  the  peculiar  arrangement  of  the  vascular 
tissue  in  the  cellular  in  the  cross-section.  Some  coal  Tree-ferns  had 
their  large  fronds  in  two  vertical  ranks  (Megaphyton — 'Fig.  471). 

The  Ferns  of  the  Coal  are, 
therefore,  unmistakably  Ferns, 
yet  botanists  recognize  some 
features  which  connect  them 
with  other  classes.  Caruthers 


FIG.  471.— Megaphyton,  a  Coal-Fern 
FIG.  470.— Living  Tree-Fern.  restored  (after  Dawson). 

thinks  that  he  finds  in  the  internal  structure  of  the  stems  of  Tree-ferns 
of  the  Coal  two  types  which  are  the  foreshadowings  of  the  Monocotyls 
on  the  one  hand,  and  the  Dicotyls  on  the  other ;  and  that  therefore 
they  are  probably  the  progenitors,  not  only  of  the  Tree-ferns  of  the 
present  day,  but  also  of  the  Palms  and  the  foliferous  Exogens.* 

*  Nature,  vol.  vi,  p.  480,  and  Scott,  American  Journal,  vol.  ix,  p.  45. 


PLANTS  OF  THE   COAL. 


363 


The  next  three  orders  we  will  discuss  more  fully  for  two  reasons : 
First,  the  Conifers  were  probably  mostly  highland  plants,  and  only 
found  their  way  into  the  coal-swamps  by  accident,  being  in  fact  brought 
down  by  freshets.  The  Ferns  formed  the  thick  underbrush  of  the  coal- 
swamps.  Neither  of  these  contributed  a  very  large  share  to  the  mate- 
rial of  the  coal-seams.  The  great  trees  of  the  coal-swamps,  and  which 
formed  the  larger  part  of  the  material  preserved  as  coal,  were  Lepido- 
dendrids,  Sigillarids,  and  Calamites. 

Again,  the  Conifers  and  Ferns  were  unmistakably  Conifers  and 
Ferns,  though  certainly  with  characters  connecting  with  other  orders 
and  classes ;  but  the  three  orders  now  about  to  be  discussed  combine  so 


FIG.  474. 


FIG.  476. 


FIG.  472.  FIG.  473.  x- !«.•*<<*.  no.  *vo. 

FIGS.  472-476.— COAL-FERNS :  472.  Callipteris  Sullivanti  (after  Leeqnere.ux).  473.  Pecopteris  Strong!! 
(after  Lesquereux).  474.  Alethopteris  Massilonis  (after  Lesquereux).  475.  Same  enlarged  to 
show  dichotomous  venation.  476.  Neuropteris  flexuosa  (after  Brongniart). 

completely  the  characters  of  widely-separated  classes  that  there  is  still 
some  doubt  as  to  their  real  place.  For  that  very  reason,  however,  they 
are  peculiarly  interesting  to  the  evolutionist. 


364 


PALAEOZOIC  SYSTEM   OF   ROCKS. 


FIG.  480. 


FIG.  481. 


FIG.  483. 


FIGS.  477^184.— COAL- FERNS  (after  Lesquereux):  477.  Pecopteris  Strongii,  showing  fructification; 
6,  a  leaflet  enlarged.  478.  Odontopteris  Wortheni.  479.  Hymenophyllites  alatus.  480.  Neu- 
roptens  flexuosa.  481.  Neuropteris  hirsuta.  482.  Alethopteris  lonchitica.  483.  Odontopteris 
gracillima  (after  Newberry).  484.  Hymenophyllites  splendens  (after  Lesquereux). 


PLANTS  OF  THE   COAL. 


365 


FIG.  485. 


Fia.  486. 


FIG.  487. 


FIGS.  485-487.— COAL- FEKNS  :  485.  Leaf  Scars  of  Palaeopteris,  x  }  (after  Dawpon).    486.  Leaf-Scar  of 
Megaphyton,  x  £  (after  Dawson).    487.  Caulopteris  primeva,  showing  Leaf-Scars. 

3.  Lepidodendrids.  —  These  are  so  called  from  the  typical  genus 
Lepidodendron.     We  will  describe  only  this  genus. 

Lepidodendrons  are  found  most  commonly  in  flattened  masses  rep- 
resenting portions  of  the  trunk  or  branches,  very  regularly  marked  in 
rhomboidal  pattern,  and  much  resembling  the 
impression  of  the  scaly  surface  of  a  Ganoid 
fish.  The  name  Lepidodendron  (scale-tree) 
is  derived  from  this  fact  (Figs.  489  to  491). 
These  marks  are  the  scars  of  the  regularly-ar- 
ranged and  crowded  leaves.  All  portions  of 
the  plant,  however,  viz.,  the  roots,  the  trunk, 
the  branches,  the  leaves,  and  the  fruit,  have 
been  found  in  abundance.  From  these  the 
general  appearance  of  the  tree  has  been  ap- 
proximately reconstructed.  Imagine,  then,  a 
tree  two  to  four  feet  in  diameter  at  base,  forty 
to  sixty  feet  high,  with  wide-spreading  roots, 
well  adapted  for  support  on  a  swampy  soil; 
the  surface  of  the  trunk  and  branches  regu- 
larly marked  in  rhomboidal  pattern,  repre- 
senting the  phyllotaxis;  the  trunk  dividing 
and  subdividing,  but  not  profusely,  into 
branches  which  are  thickly  clothed  with  scale-  FIG.  488.— Restoration  of  a  Lepi- 

,.,  .        ,.,  ,,     ,.,       ,  /T,.  dodendron,  by  Dawsou. 

like,  or  spine-like,  or  needle-like  leaves  (Figs. 

492  and  494),  and  terminated  by  a  club-shaped  extremity  (Figs.  493, 
495,  and  496)  like  the  terminal  cones  of  some  conifers,  or  still  more 
like  the  club-shaped  extremities  of  club-moss  branches — and  we  will 
have  a  tolerably  correct  idea  of  the  Lepidodendron. 


366 


PALEOZOIC  SYSTEM  OF  BOOKS. 


The  general  appearance  of  the  tree  is  that  of  an  Araucarian  conifer, 
or  of  a  gigantic  club-moss.  The  fruit,  however,  turns  the  scale  of  affin- 
ity in  favor  of  the  club-moss ;  for  the  examination  of  these,  which  are 


FIG.  494. 


FIG.  493. 


FIG.  496. 


FIGS.  489-496.— LEPIDODENDKIDS:  489.  Lepidodendron  raodulatum  (after  Lesquerenx).  490.  Lepi- 
dodendron  diplotegioides  (after  Lesquereux).  491.  Lepidodendron  politum  (after  Lesquereux). 
492.  Lepidodendron  corrugatum,  branch  and  leaves  (after  Dawscn).  493.  Lepidodendron  cor- 
rugatum,  branch  and  frnit  (after  Dawson).  494.  Lepidodendron  rigens  (after  Lesquereux)^ 
495.  Lepidophloios  Acadianus,  fruit  (after  Dawson).  496.  Lepidostrobus  (after  Lesquereux). 


PLANTS   OF  THE   COAL. 


367 


found  in  great  abundance,  and  known  under  the  name  of  Lepidostrobus 
(scale  -  cone),  has  shown  that  they  bear  in  the  axils  of  their  scales 
spores  like  club  -  mosses, 
and  not  seeds  like  coni- 
fers. Also,  like  club-moss- 
es, there  are  in  these 
plants  two  kinds  of  spores* 
— microspores  and  macro- 
spores.  This  would  again 
ally  them  with  conifers, 
for  these  organs  may  be 
said  to  represent  the  sta- 
mens and  pistils  of  higher 
plants  (Fig.  497).  The  ex- 
ternal appearance  and  in- 
florescence, therefore,  in- 
dicate that  they  are  Lyco- 
pods,  with  very  strong 
coniferous  affinities. 

This  conclusion  is  en- 
tirely borne  out  by  the 
internal  structure.  Fig. 
498  represents  an  ideal 
cross  and  longitudinal  sec- 
tion of  the  stem  of  a  Lep- 
idodendron.  It  is  seen 
that  the  stem  consists  of 
a  dense  outer  bark  or  rind, 
inclosing  a  great  mass  of 
loose  cellular  tissue  or  in- 
ner bark,  through  the  center  of  which  runs  a  comparatively  small  fibro- 
vascular  cylinder,  with  very  distinct  pith.  Bundles  go  from  the  cylin- 
der outward  to  form  the  venation  of 
the  leaves.  Now,  the  structure  of  a 
club-moss  is  almost  the  same,  except 
that  the  fibro- vascular  cylinder  is  solid, 
and  there  is,  therefore,  no  pitli.  The 
presence  in  Lepidodendron  of  a  dis- 
tinct pith  is  an  important  character, 
placing  it  far  above  modern  Lycopods, 
and  allying  it  most  decidedly  with  Ex- 

inner  bark;  d,  rind;  e,  bases  of  leaves; 

/,  vascular  threads  going  to  the  leaves.      OgenS. 


FIG.  497.— Lepidodendron  compared  with  Club-Moss:  a,  club- 
moss;  b,  b',  scales  enlarged;  c,  microspores;  cf,  macro- 
spores;  x,  lepidostrobus;  y  and  z,  the  scales  containing 
spores;  m,  microepores;  n,  macrospores  (after  Balfour). 


*  Williamson,  Nature,  vol.  viii,  p.  498. 


368 


PALAEOZOIC   SYSTEM   OF   ROCKS. 


4,  Sigillarids, — The  typical  genus  of  this  family  is  Sigillaria. 
These  plants  are  found,  like  Lepidodendrids,  mostly  as  flattened  masses, 
which  are  portions  of  trunks,  but  also  as  roots  and  leaves.  The  trunk- 


FIG.  501. 


FIG.  503. 


FIGS.  499-503.— SIGILLARIDS:  499.  Si^illaria  reticulata  (after  Lesquerenx).  500.  Sigillaria  Gneseri. 
501.  Sigillaria  laevigata  (European).  502.  Sigillaria  obovata  (after  Lesquereux).  503.  Leaf  of 
Sigillaria  elegans  (after  Dawson). 

impressions  are  distinguished  from  those  of  Lepidodendrids  by  longi- 
tudinal ribbings  or  flutings,  ornamented  with  seal-like  impressions 
(sigilla,  a  seal),  in  vertical  rows  (Figs.  499-502).  Little  is  known  of 
their  leaves,  though  they  seem  to  have  been  similar  to  those  of  Lepido- 
dendron  (Fig.  503). 

The  best  general  conception  which  we  can  form  of  the  Sigillaria 
would  represent  it  as  a  tall,  gently-tapering  trunk,  longitudinally  fluted 


PLANTS  OF  THE  COAL.  369 

like  a  Corinthian  column,  and  ornamented  with  seal-like  impressions  in 
vertical  ranks,  representing  the  phyllotaxis ;  unbranched  or  else  divid- 
ing only  into  a  few  large  branches,  clothed 
thickly  with  long,  stiffish,  tapering  leaves. 
From  the  base  of  the  trunk  extended  large, 
radiating  roots,  branching  dichotomously  and 
sparsely,  with  many  long,  thread-like  root- 
lets penetrating  the  soil  below.  The  stumps 
of  Sigillaria  and  Lepidodendrons,  with  these 
large,  horizontally-spreading  roots  and  thread- 
like appendages,  are  very  common  in  the 
under-clay,  and  were  long  supposed  to  be  a 
peculiar  plant,  and  called  Stigmaria,  on  ac- 
count of  the  round  Spots  (stigma)  On  their  FIG.  504.— Stigmaria  flcoides  (after 

surface  (Fig.  504).    They  are  now  known  to 

belong  to  Sigillarids  and  Lepidodendrids,  and  are  either  roots  or  spread- 
ing rhizomes  (underground  branches). 

In  the  following  figure  (505),  taken  from  Dawson,  we  have  at- 
tempted to  realize  the  general  appearance  of  a  Sigillaria.  Their  trunks 
were  sometimes  of  prodigious  length  and  diameter.  They  were  prob- 
ably the  largest  trees  of  the  time.  In  a  coal-seam  in  Dauphin  County, 
Pennsylvania,  flattened  stems  were  found  four  feet  and  even  five  feet 
in  width.  Some  of  these  were  exposed  for  fifty  feet,  with  but  little 
apparent  diminution.  One  was  exposed  sixty-five  feet,  and  was  esti- 
mated to  have  extended  at  least  thirty  feet  more.  Another  was  exposed 
seventy  feet,  and  was  estimated  to  have  been  eighty  to  one  hundred 
feet  when  growing.* 

The  Sigillarids  are  regarded  as  closely  allied  to  the  Lepidodendrids. 
Indeed,  the  two  families  shade  into  each  other  in  such  wise  that  there 
are  many  genera  the  position  of  which,  whether  in  the  one  family  or  in 
the  other,  is  doubtful.  The  typical  Sigillaria,  however,  differs  in  gen- 
eral port  from  the  typical  Lepidodendron,  chiefly  in  possessing  a  more 
Palm-like,  or  Cycas-like,  or  Dracena-like  stem.  They  are  evidently, 
like  the  Lepidodendrids,  closely  allied  to  Lycopods,  but  their  alliance 
with  higher  classes  is  even  stronger  than  that  of  Lepidodendrids. 

The  internal  structure  of  the  stem  entirely  confirms  this  conclusion. 
A  cross-section  (Fig.  506)  of  a  Sigillaria-stem  shows  a  hard  external 
rind,  d,  inclosing  a  great  mass  of  loose,  cellular  tissue  (inner  bark), 
c  c,  through  the  center  of  which  runs  a  comparatively  small  woody 
cylinder,  b  b,  and  in  the  center  of  this  again  a  large  pith,  a  a.  From 
the  woody  cylinder  go  bundles  of  fibro- vascular  tissue,  ffy  through  the 
cellular  tissue  of  the  inner  bark,  to  the  leaves,  e  e.  Thus  far  the  de- 

*  Taylor,  Statistics  of  Coal,  pp.  149,  160;  Williamson,  Nature,  vol.  riii,  p.  447. 

24 


370 


PALEOZOIC   SYSTEM   OF  ROCKS. 


scription  is  like  the  Lepidodendron,  except  that  the  woody  cylinder  is 
larger  and  thicker ;   but  closer  examination  shows,  in  addition,  the 

woody  cylinder  divided  into  woody 
wedges  by  medullary  rays,  g  g,  in 
true  exogenous  style,  though  the 
concentric  rings  characteristic  of 
Exogens  are  wanting.  Still  closer 
examination  with  the  microscope 
shows  a  true  gymnospermous  tis- 
sue (page  328,  Figs.  389  to  391), 
both  on  cross  and  longitudinal  sec- 
tion. Now,  there  is  no  plant  living 
which  combines  gymnospermous 
tissue  with  a  general  stem-structure 
at  all  similar  to  this,  except  Cycads 
(Cycas,  Zamia,  etc.).  For  the  sake 
of  comparison,  we  have  given  (Fig. 
507)  a  cross-section  of  a  Cycas; 
the  letter's  represent  the  same  as  in 
the  previous  figure.  There  can  be 

FiG.505.-RestorationofSigillaria,byDawson.     no  reas0nable  doubt,   therefore,   of 

the  close  alliance  of  the  Sigillarids  with  the  Cycads.     But  their  close 
connection  with  Lepidodendrids  shows  an  equally  close,  or  closer,  alli- 


Fio.  506.— Ideal  Section  of  a  Sigillaria-Stem:  a,  pith; 
ft,  woody  cylinder;  c,  inner  bark;  d,  rind;  e,  bases 
of  leaves;  /,  vascular  thread  running  to  the 
leaves;  g,  medullary  rays. 


FIG.  507.— Cross-Section  of 
Stem  of  Cycas. 


ance  with  Lycopods.  So  thoroughly  are  they  a  connecting  type  that 
some  paleontological  botanists  (Dawson)  regard  them  as  Oycads  with 
strong  Lycopod  affinities,  while  most  regard  them  as  Lycopods  with 
strong  Cycad  affinities.  Eecent  investigations  seem  to  substantiate  the 
latter  view ;  for,  in  connection  with  Sigillaria,  inflorescence  similar  to 
that  of  Lepidodendrons,  and  containing  spores,  have  been  at  last  found.* 
5.  Calamites. — These  are  plants  having  long,  slender,  tapering,  reed- 


*  Annales  des  Sciences  Botaniques,  vol.  xix,  p.  256,  1884. 


PLANTS   OF  THE   COAL. 


371 


like  stems,  jointed  and  hollow,  or  else  with  large  pith.  The  exterior 
surface  of  the  stem  is  finely  striated  or  fluted,  but  the  strise  are  not  con- 
tinuous nor  marked  with  leaf -scars  like  the  flutings  of  the  Sigillaria,  but 

are  interrupted  at  the  joints 
in  the  manner  shown  in 
Figs.  508  and  509.  At  the 
joints  are  attached  in  whorls 
the  leaves,  which  are  either 
scale-like,  or  strap-like,  or 
thread-like.  Sometimes  at 
the  joints  of  the  main  stem 
come  out  in  whorls  thread- 
like, jointed  branches,  bear- 
ing scale-like  or  thread-like 


FIG.  511.  FIG.  512. 

FIGS.  508-512. — CALAMITES  AND  THEIR  ALLIES:  508.  Lower  End  of  Stem  of  Calamites  from  Nova 
Scotia.  509.  Lower  End  of  Stem  of  Calamites  cannseformie.  510.  Sphenophyllum  erosum 
(after  Dawson).  511.  Asterophyllites  foliosue,  England  (after  Nicholson).  512.  Annularia  in- 
flata  (after  Lesquereux). 

leaves.  At  the  lower  end  of  the  stem,  the  joints  grow  rapidly  smaller 
and  shorter,  so  that  this  end  was  conical.  From  these  short,  rapidly- 
tapering  joints  came  out  the  tliread-like  roots.  The  stem  was  termi- 
nated above  with  a  cone-like  fruit  (Fig.  513). 

What  I  have  said  thus  far  applies  word  for  word  to  Equisetae ;  but 
the  Equisetae  of  the  present  day  are  small,  rush-like  plants,  never  much 
thicker  than  the  finger,  and  seldom  more  than  three  or  four  feet  high, 
although  in  South  America  (Caracas)  they  grow  thirty  feet  high,  but 
are  very  slender ;  while  Calamites  were  certainly  two  feet  or  more  in 
diameter,  and  thirty  feet  high.  Fig.  514  is  an  attempt  to  reconstruct 
the  general  appearance  of  a  Calamite  by  Dawson. 

The  internal  structure  of  Calamites  still  further  removes  them  from 
Equisetae ;  for  they  seem  to  have  had  (some  of  them,  at  least)  a  thick, 


372 


PALAEOZOIC   SYSTEM   OF   ROCKS. 


woody  cylinder  of  exogenous  structure  and  gymnospermous  tissue.  And 
if,  as  Williamson  supposes,*  many  of  the  striated  jointed  stems  called 

Calamites  are  only  casts  of  the  pith,  the 
stems  must  have  been  even  much  larger 
than  stated  above. 

Thus,  as  Lepidodendrids  connected 
Lycopods  with  Conifers,  and  Sigillarids 
connected  Lycopods  with  Cycads,  so 
these  connected  Equisetae  with  Conifers. 
General  Conclusion. — The  conclusion 
which  we  draw  from  this  examination 
of  Coal  plants  is:  1.  That  they  belong 
to  the  highest  Cryptogams,  viz.,  Vascu- 
lar Cryptogams,  and  the  lowest  Phsencb- 
gams,  viz.,  Gymnosperms  ;  2.  That  they 
were  intermediate  between  these  now 
widely-separated  classes,  and  connected 
them  closely  together.  These  facts  are 
strictly  in  accordance  with  the  law 

F,*.5i8.-Frnit  P.*.  5i4.-Restoration  already  announced  (page  344),  viz,  that 
of  caiamite        of  a  Caiamite  (after  the  earliest  representatives  of  any  class 

(after  Herr).  Dawson).  •'        .  . 

or  order  are  not  typical  representatives 

of  that  class  or  order,  but  connecting  or  comprehensive  types — that  is, 
types  which,  along  with  their  distinctive  classic  or  ordinal  character, 
united  others  which  connected  them  with  other  classes  or  orders. 
Thus  the  now  widely-separated  classes  and  orders  of  organisms,  when 
traced  backward,  in  time  approach  each  other  more  and  more,  and 
probably  unite  in  one  common  stem,  although  we  are  seldom  able  to 
find  the  point  of  actual  union.  Thus,  in  this  case,  the  now  widely- 
separated  Cryptogams  and  Phaenogams,  when  traced  backward,  ap- 
proach until  in  the  Coal  they  are  nearly,  if  not  completely,  united. 
The  organic  kingdom  may  be  compared  to  a  tree  whose  trunk  is  proba- 
bly to  be  found,  if  found  at  all,  in  the  lowest  strata ;  its  main  branches 
begin  to  separate  in  the  Palaeozoic,  the  secondary  branches  in  the  Mes- 
ozoic,  and  so  the  branching  continues  until  the  extreme  ramification, 
but  also  the  flower  and  fruit,  are  found  in  the  fauna  and  flora  of  the 
present  day.  The  duty  of  the  evolutionist  is  to  trace  each  bough 
to  its  fellow-bough,  and  each  branch  to  its  fellow-branch,  and  thus 
gradually  to  reconstruct  this  tree  of  life,  and  determine  the  law  and  the 
cause  of  its  growth. 


*  Nature,  vol.  viii,  p.  447. 


THEORY   OF  THE   ACCUMULATION   OF  COAL.  373 

Theory  of  the  Accumulation  of  Coal. 

There  is  no  question  connected  with,  the  Carboniferous  period  con- 
cerning which  there  has  been  more  discussion  than  the  mode  in  whicli 
coal  has  been  accumulated.  There  are  some  things,  however,  about 
which  there  is  little  difference  of  opinion.  These  we  will  state  first, 
and  thus  narrow  the  field  of  discussion. 

Presence  of  Water. — That  coal  has  been  accumulated  in  the  pres- 
ence of  water,  or  at  least  of  abundant  moisture,  is  evident :  a.  From  the 
preservation  of  the  organic  matter.  By  aerial  decay  vegetable  matter 
is  either  entirely  consumed,  or  else  crumbles  into  dust.  Only  in  the 
presence  of  water  is  it  preserved  and  accumulated  in  larger  quantities. 
b.  The  interstratified  sand  and  clays  and  limestones  have,  of  course, 
been  deposited  like  all  strata  in  water,  c.  The  coal  itself  is  not  un- 
frequently  distinctly  and  finely  stratified,  d.  The  plants  found  in  con- 
nection with  the  coal-seams  are  mostly  such  as  grow  in  moist  ground. 

Thus  far,  then,  theorists  agree,  but  from  this  point  opinions  diverge, 
and  until  recently  have  very  widely  diverged.  Some  have  thought 
that  coal  has  accumulated  by  the  growth  of  plants  "  in  situ"  as  in 
peat-bogs  and  peat-swamps  of  the  present  day.  Others  have  sup- 
posed that  it  has  accumulated  by  driftage  of  vegetable  matter  by  rivers, 
like  the  rafts  now  found  at  the  mouths  of  great  rivers  of  the  present 
day.  According  to  the  one  view,  a  coal-seam  is  an  ancient  peat-swamp  ; 
according  to  the  other,  it  is  an  immense  buried  raft.  The  one  is  called 
the  "  Peat-bog  theory"  the  other,  the  Estuary  or  raft  theory. 

Recently,  however,  scientific  opinions  have  converged  toward  a 
common  belief.  We  will  not,  therefore,  discuss  these  two  rival  theo- 
ries, but  simply  bring  out  what  is  most  certain  in  the  present  views  on 
this  subject : 

^  1.  Coal  has  been  accumulated  by  growth  of  vegetation  in  situ,  as 
in  peat-swamps  of  the  present'  day^)  This  fact  is  now  demonstrable. 
The  reasons  for  believing  it  are  the  following :  a.  The  purity  of  coal. 
The  coals  of  the  American  coal-fields  are,  with  few  exceptions,  abso- 
lutely pure,  i.  e.,  the  amount  of  ash  is  not  greater  than  would  result 
from  the  ash  of  the  plants  of  which  it  is  composed.  The  same  is  true 
of  coals  of  most  extensive  coal-fields  everywhere.  Now,  it  has  already 
been  shown  (p.  142)  that  in  extensive  peat-swamps,  like  the  Great  Dis- 
mal Swamp,  absolutely  pure  vegetable  accumulations  unmixed  with 
sediment  occur ;  but  in  buried  rafts  or  drifted  vegetable  matter  of  any 
kind  there  must.be  a  large  admixture  of  mud.  b.  The  preservation  of 
the  most  complex  and  delicate  parts  of  the  plant  in  their  natural  rela- 
tions to  each  other.  Large  fronds  are  spread  out  and  pressed  as  in  a 
botanist's  herbarium.  Delicate  leaves  are  preserved  with  all  their  finest 
venation  perfectly  visible.  This  is  exactly  what  we  would  expect  if 


374 


PALAEOZOIC   SYSTEM   OF   ROCKS. 


they  lay  where  they  fell,  but  it  is  incompatible  with  driftage  by  rapid 
currents  to  long  distances,  c.  The  position  of  these  perfect  specimens 
only  on  the  upper  part  of  the  seam,  as  would  be  the  case  with  the  last 
fallen  leaves,  instead  of  mixed  throughout  the  seam,  as  would  be  the 
case  with  drifted  matter,  d.  The  presence  of  stumps  with  their  spread- 
ing roots  penetrating  the  under-day  exactly  as  they  greiu.  This  is  not 
an  occasional  phenomenon,  but  is  found  in  the  under-clay  of  nearly 
every  coal-seam  In  South  Wales  there  are  100  seams  of  coal,  every 
one  of  which  is  underlaid  by  clay  crowded  with  roots  and  sometimes 
with  stumps.  In  Nova  Scotia  there  are  seventy-six  seams,  twenty  of 
which  have  erect  stumps  standing  in  their  original  position  with  spread- 
ing roots  still  penetrating  the  under-clay.  The  other  seams  have  each 
its  under-clay  filled  with  stigmaria-roots.  Besides  these  seams  there  are 
many  dark  bands  (dirt-beds)  indicating  old  forest-grounds. 

The  following  section  (Fig.  515)  shows  some  of  these  seams  and 
dirt-beds  or  forest-grounds,  with  penetrating  roots  and  erect  trunks. 
Fig.  516  shows  an  area  of  about  one  quarter  acre  of  surface  of  the 

under-clay  of  an  English 
coal-seam  in  which  there 
are  seventy-three  stumps 
in  situ.  This  last  evi- 
dence (d)  is  demonstra- 
tive. Beneath  every  coal- 
seam  there  is  a  fossil  soil — 
an  ancient  forest-ground. 
Recapitulation.  —  We 
may  sum  up  the  evidence, 
and  at  the  same  time  make 
it  clearer,  by  describing  a 
section  of  a  peat-bog,  and  comparing  with  a  coal-seam.  In  such  a  sec- 
tion we  have  always  an  under-clay,  on  which  accumulated  the  moisture, 
and  on  which  grew  the  original  trees  of  the  locality.  This  under-clay 
is  often  full  of  roots  and  stumps  of  the  original  growth.  Above  this  is 
a  fine,  structureless,  carbonaceous  mass,  corresponding  to  the  coal- 
seam.  On  this  are  the  last-fallen  leaves,  not  yet  disorganized,  and  the 
still-growing  vegetation.  Now,  imagine  this  overwhelmed  and  buried 
by  mud  or  sand,  the  whole  subjected  to  powerful  pressure,  and  a  slow 
subsequent  process  of  bituminization ;  and  we  have  a  complete  repro- 
duction of  the  phenomena  of  a  coal-seam  with  its  accompanying  under- 
clay  filled  with  roots,  and  its  black  shale  filled  with  leaf  and  branch 
impressions. 

/Y       2.  Coal  has  been  accumulated  at  the  mouths  of  rivers,  and  therefore 

I  in  localities  subject  to  floods  by  the  river  and  incursions  by  the  sea.    It 

is  otherwise  impossible  to  account  for  the  clays  and  sands  (often  inclos- 


FIG.  515.— Erect  Fossil  Trees,  Coal -Measures,  Nova  Scotia. 


THEORY  OF  THE  ACCUMULATION   OF   COAL. 


375 


FIG.  516. — Ground-Plan  of  a  Fossil  Forest,  Parkfield 
Colliery. 


ing  drift- timber),  and  limestones,  interstratified  with  the  coal.  The 
phenomena  of  an  individual  seam  prove  the  accumulation  by  growth 
in  situ;  the  general  phe- 
nomena of  a  coal-basin,  with 
its  succession  of  strata,  prove 
that  this  took  place  at  the 
mouths  of  rivers.  Thus,  the 
field  of  discussion  is  nar- 
rowed to  very  small  limits. 

We  conclude,  therefore, 
that  coal  has  been  accumu- 
lated in  extensive  peat- 
swamps  at  the  mouths  of 
great  rivers,  and  therefore 
subject  to  occasional  flood- 
ings  by  the  river  and  inun- 
dations by  the  sea.  That  pure  peat  may  accumulate  under  these  cir- 
cumstances, is  sufficiently  proved  by  the  fact  mentioned  by  Lyell,  that 
over  large  tracts  of  ground  in  the  river-swamp  and  delta  of  the  Missis- 
sippi pure  peat  is  now  forming,  in  spite  of  the  annual  floods ;  the  sedi- 
ments being  all  stopped  by  the  thick  jungle-growth  surrounding  these 
spots,  and  deposited  on  the  margins,  while  only  pure  water  reaches  the 
interior  portions.* 

But  if  coal  has  indeed  been  formed  at  the  mouths  of  great  rivers,  we 
ought  to  find  at  least  something  analogous  to  a  coal-field  in  sections  of 
great  river-deltas.  And  so,  indeed,  we  do.  We  have  seen  (p.  136)  that 
a  great  river-delta,  like  that  of  the  Mississippi  or  the  Ganges,  consists 
of  alternate  layers  of  river-sediments  (sands  and  clays)  and  marine  sedi- 
ments (limestones)  with  thin  layers  of  peaty  matter,  and  old  forest- 
grounds  with  stumps  and  roots.  It  is,  in  other  words,  a  coal-field, 
though  an  imperfect  one,  in  the  process  of  formation.  It  will  be  re- 
membered, also,  that  we  accounted  for  this  alternation,  not  by  oscilla- 
tions, but  by  the  operation  of  two  opposing  forces,  one  depressing  (sub- 
sidence), the  other  up-building  (river-deposit),  with  varying  success. 
When  the  up-building  by  river-deposit  prevailed,  the  area  was  reclaimed, 
and  became  covered  with  thick  jungle  vegetation ;  when  the  subsidence 
prevailed,  it  was  again  covered  with  water,  and  buried  in  river-sedi- 
ments, etc.  Now  and  then,  when  the  subsidence  was  unusually  great, 
the  sea  invaded  the  same  area,  and  limestone  was  formed.  It  is  sub- 
stantially in  this  way  that  coal-fields  were  probably  formed. 

Application  of  the  Theory  to  the  American  Coal-Fields  :  a.  Appala- 
chian Coal-Field. — A  glance  at  the  map  (p.  291)  will  show  that,  during 


*  Lyell,  Elements  of  Geology,  p.  488. 


376  PALEOZOIC  SYSTEM   OF  KOCKS. 

Carboniferous  times,  there  was  high  land  to  the  north,  east,  and  west  of 
this  field,  and  the  black  area,  representing  the  Coal-measures,  was  then  a 
trough,  into  which,  therefore,  drained  rivers  from  every  side  except  the 
south.  This  trough  was  sometimes  a  coal-swamp,  sometimes  a  lake 
emptying  southward,  sometimes  an  arm  of  the  sea  connecting  with  the 
ocean  southward.  When  it  was  a  coal-marsh,  a  coal-seam  was  formed  ; 
when  a  lake,  sands  and  clays  were  deposited  by  the  rivers ;  when  an 
arm  of  the  sea,  marine  deposits — limestones — were  formed. 

This  alternation  of  conditions  we  explain  as  follows :  There  were 
three  forces  at  work  on  this  area :  1.  A  general  continental  upheaval, 
affecting  this  along  with  all  other  parts  of  the  continent ;  2.  An  up- 
building by  sedimentary  deposit.  3.  A  local  subsidence.  The  evidence 
of  all  these  is  complete.  The  continental  upheaval,  as  we  have  already 
seen,  was  unceasing  throughout  the  previous  periods,  and,  as  we  shall 
see,  continued  throughout  the  subsequent  periods.  The  up-building  by 
sediments  and  the  part  passu  subsidence  are  as  clearly  marked  as  in 
deltas  of  the  present  day,  by  shore-marks,  by  shallow-water  fossils,  and 
especially  by  forest-grounds  repeated  through  several  thousand  feet  of 
vertical  thickness.  The  existence  of  these  three  forces,  therefore,  is 
not  a  doubtful  hypothesis.  Now,  the  first  two  would  tend  to  reclaim, 
the  third  to  submerge,  the  area.  When  the  reclaiming  forces  pre- 
dominated, the  area  became  swamp-land,  and  covered  with  coal  vegeta- 
tion, and  the  river- water,  strained  through  the  thick  growth,  slowly  went 
southward  by  a  kind  of  seepage.  When  the  submerging  forces  pre- 
dominated, the  area  became  a  lake,  and  sediments  in  great  quantities 
were  brought  down  by  the  rivers.  It  is  possible,  perhaps  probable,  that 
correlative  with  the  more  rapid  local  subsidence  which  formed  the  lake 
there  was  also  a  more  rapid  elevation  of  the  high  lands  on  all  sides,  pro- 
ducing more  torrential  river-currents  and  greater  sedimentary  deposits. 
Now  and  then,  at  long  intervals,  the  subsidence  would  bring  the  area 
below  sea-level,  and  would  thus  form  an  interior  sea,  or  mediterranean. 
During  such  times,  limestones  would  be  formed,  and  marine  animals 
would  be  imbedded  as  fossils. 

b.  Western  Coal-Fields. — The  Central  and  Western  coal-fields  may 
be  regarded  as  one,  having  been  subsequently  separated  by  denudation. 
This  immensely  extensive  field  may  have  been,  like  the  Appalachian,  a 
hollow  surrounded  on  all  sides  by  higher  land.  If  so,  the  western  land 
has  since  been  submerged,  and  covered  by  more  recent  deposits.  Or  it 
may  have  been  an  extensive  jungly  flat,  bordering  a  western  sea,  the 
many  small  rivers  with  inosculating  deltas,  flowing  westward  and  seep- 
ing through  the  thick,  marshy  vegetation.  There  were  here  far  less 
mechanical  sediments,  because  less  high  land,  and  far  more  marine 
deposits,  because  there  was  a  larger  and  opener  sea ;  but,  in  other  re- 
spects, the  process  may  be  regarded  as  similar. 


ESTIMATE   OF   TIME.  377 

Appalachian  Revolution. — This  state  of  oscillation  and  incertitude 
was  cut  short  by  the  Appalachian  revolution.  At  the  end  of  the  Coal 
period,  the  sediments  which  had  been  so  long  accumulating  in  the 
Appalachian  region,  until  their  aggregate  thickness  had  now  reached 
40,000  feet,  at  last  yielded  to  the  horizontal  pressure  produced  by  in- 
terior contraction  of  the  earth  (p.  263),  and  were  crumpled,  and  mashed, 
and  thickened  up  into  the  Appalachian  chain.  At  the  same  time  the 
Western  coal-swamps  were  upheaved  sufficiently  to  become  permanent 
dry  land.  This  revolution  closed  the  Carboniferous  age  and  the 
Palaeozoic  era. 

Estimate  of  Time. 

We  have  said  (p.  276)  that  it  is  important  that  the  mind  become 
familiarized  with  the  idea  of  the  immense  time  necessary  to  explain 
geological  phenomena.  We  therefore  embrace  this  opportunity  to 
make  a  rough  estimate  of  the  Coal  period.  The  estimate  may  be  made 
either  by  taking  the  whole  amount  of  coal  in  a  coal-field  as  the  thing  to 
be  measured,  and  the  rate  at  which  vigorous  vegetation  now  makes  or- 
ganic matter  as  the  measuring-rod ;  or  else  by  taking  the  whole  amount 
of  sediments  in  a  coal-basin  as  the  thing  to  be  measured,  and  the  rate 
of  accumulation  of  sediments  by  large  rivers  as  the  measuring-rod. 
We  will  give  both,  though  the  latter  is  probably  the  more  reliable  : 

1.  From  Aggregate  Amount  of  Coal. — A  vigorous  vegetation — as, 
for  example,  an  average  field-crop  or  a  thick  forest — makes  about  2,000 
pounds  of  dried  organic  matter  per  annum  per  acre,  or  200,000  pounds 
or  100  tons  per  century.*     But  100  tons  of  vegetable  matter  pressed 
to  the  specific  gravity  of  coal  (T4),  and  spread  over  an  acre,  would  make 
a  layer  less  than  two  thirds  of  an  inch  in  thickness.     But,  according 
to  Bischof,  vegetable  matter  in  changing  to  coal  loses,  on  an  average, 
four  fifths  of  its  weight  by  the  escape  of  C02,  CH4,  and  H80  (p.  356), 
only  one  fifth  remaining.     Therefore,  vigorous  vegetation  at  present 
could  make  only  about  one  eighth  of  an  inch  of  coal,  specific  gravity 
1*4,  per  century.     To  make  a  layer  one  foot  thick  would  require  nearly 
10,000  years.     But  the  aggregate  thickness  in  some  coal-basins  is  100 
feet,  150  feet,  or  even  250  feet  (p.  350).     This  would  require — the  for- 
mer near  1,000,000,  the  latter  2,400,000  years.    It  is  probable,  however, 
that  coal  vegetation  was  more  vigorous  than  the  present  vegetation. 
Our  measuring-rod  may  be  too  short;  we  will  try  the  other  method : 

2.  From  Amount  of  Sediment. — We  are  indebted  to  Sir  Charles 
Lyell  for  the  following  estimate  of  the  time  necessary  to  accumulate 
the  Nova  Scotia  Coal-measures.     This  coal-field  is  selected  because  the 
evidences  of  river-sediments  are  very  clear  throughout.     The  area  of 

^Recent  researches  considerably  increase  these  numbers.     Nature,  vol.  xvi,  p.  211, 

1877. 


378  PALAEOZOIC   SYSTEM   OF  ROCKS. 

this  coal-basin  is  given  on  page  350  as  18,000  square  miles ;  but  the 
identity  in  character  of  portions  now  widely  separated  by  seas — e.  g., 
on  Prince  Edward's  Island,  Cape  Breton,  Magdalen  Island,  etc. — plainly 
shows  that  all  these  are  parts  of  one  original  field,  which  could  not 
have  been  less  than  36,000  square  miles.  The  thickness  at  South  Jog- 
gins  is  13,000  feet.  At  Pictou,  100  miles  distant,  it  is  nearly  as  great. 
We  shall  certainly  not  err  on  the  side  of  excess,  therefore,  if  we  take  the 
average  thickness  over  the  whole  area  as  7,500  feet.  This  would  give 
the  cubic  contents  of  the  original  delta  deposit  as  about  51,000  cubic 
miles.  Now,  the  Mississippi  River,  according  to  Humphrey  and  Abbot, 
carries  to  its  delta  annually  sediment  enough  to  cover  a  square  mile 
268  feet  deep,  or  nearly  exactly  one  twentieth  of  a  cubic  mile.  There- 
fore, to  accumulate  the  mass  of  sediment  mentioned  above  would  take 
the  Mississippi  about  1,000,000  years. 

It  may  be  objected  to  this  estimate  that  it  is  founded  on  a  particu- 
lar theory  of  the  accumulation  of  the  Coal-measures.  The  answer  to 
this  is  plain.  Any  other  mode  would  only  extend  the  time,  for  this 
mode  is  more  rapid  than  any  other.  Again,  it  may  be  objected  that 
we  have  evidence  of  a  very  rapid  accumulation  in  stumps  and  logs  and 
erect  trunks,  either  bituminized  or  petrified,  and  which,  therefore,  must 
have  been  completely  buried  before  they  could  decay.  The  answer  is, 
that  these  are  only  examples  of  local  rapid  deposit,  and  do  not  at  all 
affect  the  general  result.  Precisely  the  same  happens  now  in  river- 
deltas.  Again,  it  may  be  objected  that  the  agencies  of  Nature  were  far 
more  energetic  then  than  now.  This  objection  has  already  been  an- 
swered on  page  277. 

We,  therefore,  return  to  our  estimate  with  increased  confidence 
that  it  is  far  within  limits.  But  the  Coal  period,  as  already  said  (p. 
346),  is  not  more  than  one  thirtieth  of  the  recorded  history  of  the 
earth ;  beyond  which,  again,  lies  the  infinite  abyss  of  the  unrecorded. 

Physical  Geography  and  Climate  of  the  Coal  Period. 

Physical  Geography. — In  the  eastern  part  of  the  American  Conti- 
nent the  area  of  land  during  this  period  is  approximately  shown  in  the 
map  (p.  291).  It  included  the  Laurentian,  the  Silurian,  and  Devonian 
areas,  during  the  whole  age.  In  the  sub-Carboniferous  period  the  sub- 
Carboniferous  and  Carboniferous  areas  were  covered  by  the  sea,  but  in 
the  Carboniferous  period  proper  the  sub- Carboniferous  area  was  land, 
and  the  Carboniferous  area,  as  already  seen,  was  in  an  uncertain  state, 
sometimes  above  and  sometimes  below  the  sea-level.  It  is  probable, 
also,  that  the  Eastern  border-land  extended  then  much  beyond  the  line 
of  the  Tertiary  deposits  (see  map,  p.  291),  and  even  beyond  the  present 
coast-line  (see  map,  Fig.  266),  and  was  partly  submerged  in  the  eleva- 
tion of  the  Appalachian  chain,  at  the  end  of  the  Coal  period. 


PHYSICAL   GEOGRAPHY  AND   CLIMATE   OF  THE   COAL  PERIOD.   379 

In  the  Rocky  Mountain  region  there  were  considerable  bodies  of 
land,  mainly  in  the  Basin  region,  but  their  limits  are  not  accurately 
known. 

Again,  it  is  almost  certain  that  all  the  lands  were  comparatively 
low.  None  of  the  great  mountain-chains  of  the  continent  were  yet 
formed.  It  is  also  probable  that  the  same  was  true  of  the  other  conti- 
nents. Nearly  all  the  high  mountain-chains  are  either  more  recent  in 
their  origin,  or  else  in  their  principal  growth.  In  general  terms,  then, 
the  lands  were  smaller  and  lower,  and  the  conditions  more  oceanic, 
than  at  present. 

xJlimate. — The  climate  of  the  Coal  period  was  undoubtedly  charac- 
terized by  greater  warmth,  humidity,  uniformity,  and  a  more  highly 
carbonated  condition  of  the  atmosphere,  than  now  obtain.  '/  Most  of 
these  characteristics,  if  not  all,  are  indicated  by  the  nature  of  the  vege- 
tation : 

1.  The  ivarmth  is  shown  by  the  existence  of  a  tropical  or  ultra- 
tropical  vegetation.     Of  the  present  flora  of  Great  Britain  about  one 
thirty-fifth  are  Ferns,  and  none  of  these  Tree-ferns.     Of  the  Coal  flora 
of  Great  Britain  about  one  half  were  Ferns,  and  many  of  these  Tree- 
ferns.     At  present  in  all  Europe  there  are  not  more  than  sixty  known 
species  of  Ferns :  in  European  Coal-measures  there  are  nearly  350  * 
species,  and  these  are  certainly  but  a  fraction  of  the  actual  number 
then  existing.     That  this  indicates  a  tropical  climate  is  shown  by  the 
fact  that  out  of  1,500  species  of  living  Ferns  known  twenty  years  ago, 
1,200,  or  four  fifths,  were  tropical  species.     The  number  of  known  liv- 
ing Ferns  is  now  about  3,000,  f  but  the  proportion  of  tropical  species  is 
still  probably  the  same.     Even  in  the  tropics,  however,  the  proportion 
of  Ferns  is  far  less  than  in  Great  Britain  during  the  Coal  period. 
Again,  Tree-ferns,  arborescent  Lycopods,  Cycads,  and  Araucarian  Coni- 
fers, are  now  wholly  confined  to  tropical  or  sub-tropical  regions.     The 
prevalence  of  these  tropical  families  and  their  immense  size,  compared 
with  their  congeners  of  the  present  day,  would  seem  to  indicate  not 
only  tropical  but  ultra-tropical  conditions.     And  these  conditions  pre- 
vailed not  only  in  the  United  States  and  Europe,  but  northward  into 
polar  regions ;  for  in  Mellville  Island,  75°  north  latitude,  and  Spitz- 
bergen,  77°  33'  north  latitude,  have  been  found  coal-strata  containing 
Tree-ferns,  gigantic  Lycopods,  Calamites,  etc. 

2.  The  humidity  is  indicated  by  the  fact  that  Tree-ferns  and  arbo- 
rescent Lycopods  are  most  abundant  now  on  islands  in  the  midst  of  the 
ocean ;  and  further  by  the  great  extent  of  the  Coal  swamps,  and  per- 
haps also  by  the  general  succulence  of,  or  the  predominance  of  cellular 
tissue  in,  the  plants  of  that  period. 


*  Lcsquereux.  f  Nature,  August,  1876. 


380  PALEOZOIC   SYSTEM   OF   ROCKS. 

3.  \The  uniformity  is  proved  by  the  great  resemblance  and  often 
identity  of  the  species  in  the  most  widely-separated  regions.^.  Accord- 
ing to  Lesquereux,  out  of  434  American  and  440  European  species,  176 
are  common,  and  the  remainder  far  less  diverse  in  character  than  the 
species  of  the  two  floras  at  present.     Again,  in  all  latitudes,  from  the 
tropics  to  75°  north  latitude,  Coal  species  are  extremely  similar.     Such 
uniformity  of  vegetation  shows  a  remarkable  uniformity  of  climate. 
From  the  earliest  times  until  the  present  there  has  been  probably  a 
gradual  evolution  of  continents — a  gradual  differentiation  of  land  and 
water,  a  consequent  differentiation  of  climates,  and  a  corresponding 
differentiation  of  faunas  and  floras. 

4.  (The  carbonated  condition  of  the  atmosphere  is  proved  by  the 
large  quantity  of  carbon  laid  up  in  the  form  of  coal,  the  whole  of  which 
was  withdrawn  from  the  atmosphere  in  the  form  of  carbonic  acid.  )  It 
is  also  indicated  by  the  nature  and  the  luxuriance  of  the  vegetation. 
The  proportion  of  carbonic  acid  in  the  atmosphere  is  now  about  -^  per 
cent  (-g-oVo-).     Now,  since  carbonic  acid  is  the  necessary  food  of  plants, 
it  is  natural  to  expect  that  up  to  a  certain  limit  the  increase  of  atmos- 
pheric carbonic  acid  would  increase  the  luxuriance  of  vegetation.     Ex- 
periments by  Daubeny  *  prove  that  this  is  true  especially  for  vascular 
Cryptogams. 

We  may  therefore  picture  to  ourselves  the  climate  of  this  period  as 
warm,  moist,  uniform,  stagnant  (for  currents  of  air  are  determined  by 
difference  of  temperature),  and  stifling,  from  the  abundance  of  carbonic 
acid.  Such  physical  conditions  are  extremely  favorable  to  vegetation, 
but  unfavorable  to  the  higher  forms  of  animal  life. 

Cause  of  this  Climate. — The  moisture  and  uniformity  were  the 
necessary  result  of  the  physical  geography  already  given.  They  were 
due  to  the  wide  extent  of  ocean  and  the  absence  of  large  continents  and 
high  mountains.  High  mountains  are  the  precipitating  points  for  the 
atmosphere — points  through  which  it  discharges  its  superabundant 
moisture.  As  these  did  not  exist,  the  atmosphere  was  always  highly 
charged.  The  prevalence  of  the  ocean  also,  as  is  well  known,  produces 
uniformity. 

The  greater  warmth  of  high  latitudes  is  partly  explained  by  the 
uniformity.  But  there  is  good  reason  to  believe  that  there  was  then 
a  higher  mean  temperature  than  now  exists.  This  was  probably  due  to 
the  constitution  of  the  atmosphere.  This  may  be  shown  as  follows  : 

The  surface-temperature  of  the  earth  is  now  almost  wholly  due  to 
external,  not  to  internal  causes.  It  has  been  calculated  that  only  one 
twentieth  of  a  degree  Fahr.  is  now  due  to  the  latter  cause.  In  going 
downward  the  heat  increases  about  1°  Fahr.  for  every  50  to  60  feet, 

*  Report  of  British  Association  for  1849,  p.  62,  and  1850,  p.  159. 


PHYSICAL  GEOGRAPHY  AND   CLIMATE   OF   THE   COAL  PERIOD. 

i.  e.,  the  internal  heat  for  every  50  feet  of  depth  increases  twenty  times 
the  surface-temperature,  so  far  as  this  is  due  to  internal  causes.  Now, 
it  has  been  shown  by  Fourier  and  Hopkins  that  the  same  would  be 
true  whatever  be  the  surface-temperature  from  internal  causes.  For 
example,  if  the  surface-temperature  from  internal  causes  be  1°,  then 
for  every  50  feet  of  depth  the  interior  heat  would  increase  20°.  If  the 
surface-temperature  from  internal  causes  be  10°,  then  for  every  50  feet 
of  depth  the  interior  heat  would  increase  200° — a  condition  of  things 
entirely  inconsistent  with  the  growth  of  plants,  since  all  the  springs 
would  be  boiling.  We  can  not,  therefore,  attribute,  as  many  have 
done,  even  a  few  degrees'  increase  of  mean  temperature  to  causes  in- 
terior to  the  earth.  In  fact,  it  seems  almost  certain  that  during  the 
whole  recorded  history  of  the  earth,  i.  e.,  during  the  time  it  has  been 
inhabited  by  organisms,  the  surface-temperature  of  the  earth  has 
been  almost  wholly  due  to  external  causes.  Now,  the  composition 
of  the  atmosphere  is  an  external  cause,  which  greatly  affects  the  sur- 
face-temperature, but  which  has  hitherto  been  almost  wholly  neg- 
lected. The  thorough  explanation  of  this  point  will  require  some  dis- 
cussion of  the  properties  of  transparent  media  in  relation  to  light  and 
heat. 

Many  bodies  which  are  transparent  to  light  are  opaque  to  heat. 
Such  bodies,  however,  will  freely  transmit  heat,  if  the  heat  be  accom- 
panied with  intense  light.  It  is  as  if  the  light  carried  the  heat  through 
with  it.  Heat  thus  associated  with  light  is  sometimes  called  light-heat, 
while  that  which  is  not  thus  associated  is  called  dark  heat.  Now,  the 
bodies  spoken  of  are  transparent  to  light-heat,  but  opaque  to  dark  heat. 
Glass  is  such  a  body.  If  a  pane  of  glass  be  held  between  the  face  and 
the  sun,  the  heat  passes  freely  and  burns  the  face,  but  the  same  pane 
would  act  as  a  partial  screen  before  a  fire,  and  as  a  perfect  screen  be- 
fore a  hot,  but  not  incandescent,  cannon-ball. 

It  is  in  this  way  we  explain  the  fact  that  a  glass  greenhouse,  even 
in  the  coldest  sunshiny  winter's  day,  becomes  insupportably  warm  if 
shut  up.  The  sun-light  and  heat  pass  freely  through  the  glass,  and 
heat  the  ground, the  benches, the  flower-pots;  but  the  light-heat  there- 
by becomes  converted  into  dark  heat,  and  thus  is  imprisoned  within.* 
Now,  the  earth  and  its  atmosphere  are  such  a  greenhouse.  The  light- 
heat  passes  readily  through,  warms  the  ground,  changes  into  dark  heat, 
and  is  in  a  measure  imprisoned  by  the  partial  opacity  of  the  atmosphere 
to  this  kind  of  heat.  The  atmosphere  is  a  kind  of  blanket  put  about 
the  earth  to  keep  it  warm.  So  much  has  long  been  recognized.  But 

*  On  Mount  Whitney,  in  the  sunshine,  Langley  got,  in  a  box  covered  with  glass,  a 
temperature  af  236°  Fahr.  or  113'3°  C.,  while  in  the  shade  of  the  open  air  the  temperature 
was  only  58'6°  F.  or  14'8°  C. 


382  PALAEOZOIC   SYSTEM  OF  ROCKS. 

Tyndall  has  shown  *  that  the  property  of  opacity  to  dark  heat  in  the 
case  of  the  atmosphere  is  due  wholly  to  the  small  quantity  of  carbonic 
acid  and  aqueous  vapor  present ;  that  oxygen  and  nitrogen  are  trans- 
parent to  dark  heat,  and,  therefore,  if  the  atmosphere  consisted  only  of 
these  two  gases,  it  would  not  be  heated  by  radiation  from  the  earth,  and 
the  ground  would  lose  all  its  heat  by  radiation  during  the  night,  and 
become  intensely  cold  like  space.  In  other  words,  the  blanket  put  about 
the  earth  to  keep  it  warm  is  woven  of  carbonic  acid  and  aqueous  vapor. 

Now,  we  have  seen  that  during  the  Coal  period  the  quantity  of  car- 
bonic acid  and  aqueous  vapor  in  the  air  was  far  greater  than  now. 
The  atmosphere  was  then  a  double  blanket,  and  therefore  kept  the 
young  earth  much  warmer.  We  believe  that  Prof.  T.  S.  Hunt  f  was 
the  first  to  apply  this  discovery  of  Tyndall  to  the  explanation  of  the 
climate  of  the  Coal  period.  E.  B.  Hunt  had  previously  attributed  it  to 
greater  density  of  the  air  (Dana,  Manual,  p.  353) ;  but  this  is  a  wholly 
different  principle.  J 

Thus  the  physical  geography  explains  the  humidity  and  uniformity, 
and  the  greater  humidity  and  the  carbonic  acid  explain  the  greater  mean 
temperature.  But  there  is  still  the  carbonic  acid  to  be  accounted  for. 

The  more  highly -carbonated  condition  of  the  atmosphere  must  be 
attributed  to  the  original  constitution  of  the  air.  All  carbonic-acid- 
producing  causes,  such  as  animal  respiration,  combustion,  general  decay 
of  organic  matter,  volcanoes,  carbonated  springs,  etc.,  only  return  to  the 
air  what  has  been  previously  taken  from  it.  There  can  be  no  doubt 
that  all  the  carbon  in  the  world,  whether  in  the  form  of  organic  matter, 
or  of  coal,  or  of  bitumen,  or  of  carbonates,  existed  once  as  carbonic  acid 
in  the  air,  and  has  been  progressively  withdrawn.  First  immense  quan- 
tities were  withdrawn  and  fixed  as  carbonates,  especially  as  carbonate  of 
lime  (limestone),  and  the  air  correspondingly  purified.  Again,  immense 
quantities  were  withdrawn  by  the  luxuriant  vegetation  of  the  Coal  pe- 
riod, and  fixed  as  coal.  In  this  latter  method  of  withdrawal  the  oxygen 
of  the  carbonic  acid  is  returned,  and  the  oxygenation  of  the  air  is  in- 
creased. We  shall  see  hereafter  that  the  process  of  purification  did  not 
cease  with  the  Coal  period ;  for  large  quantities  were  again  withdrawn 
and  laid  down  as  coal  and  lignite  in  the  Jurassic,  the  Cretaceous,  and 
Tertiary  periods.  There  can  be  no  doubt  that  this  progressive  purifica- 
tion of  the  air,  by  the  withdrawal  of  superabundant  carbonic  acid  and 
returning  the  pure  oxygen,  fitted  it  for  the  purposes  of  higher  and 
higher  animals. 

*  Proceedings  of  the  Royal  Society,  vol.  xi,  p.  100 ;  American  Journal,  second  series 
vol.  xxxvi,  p.  99. 

f  Chemical  and  Geological  Essays,  p.  42. 

\  According  to  Buff,  Archives  des  Sciences,  vol.  Ivii,  p.  293,  the  opacity  to  dark  heat 
of  carbonic  acid  and  aqueous  vapor  has  been  exaggerated  by  Tyndall. 


IRON-ORE   OF  THE   COAL-MEASURES.  383 

Iron- Ore  of  the  Coal-Measures. 

We  have  already  stated  that  the  Coal-measures  consist  of  alternat- 
ing layers  of  sandstones,  shales,  and  limestones,  containing  seams  of 
coal  and  bands  of  iron-ore.  We  have  already  discussed  the  mode  of 
occurrence,  the  varieties,  and  the  theory  of  accumulation  of  the  coal. 
We  come  now  to  discuss  the  same  points  in  regard  to  the  iron-ore. 

Mode  of  Occurrence. — The  mode  of  occurrence  of  iron-ore  is,  in 
many  respects,  like  that  of  coal.  Like  coal,  it  is  found  in  seams,  which 
vary  in  thickness  from  a  fraction  of  an  inch  to  forty  or  fifty  feet. 
Like  coal,  these  very  thick  seams  are  apt  to  be  impure,  being  largely 
mixed  with  clay.  Seams  pure  enough  to  work  profitably  are  seldom 
more  than  three  or  four  feet  thick.  Like  coal,  the  seams  are  repeated 
many  times  in  the  same  section  (Fig.  450,  p.  347),  but  without  any  dis- 
coverable order  of  succession.  Like  coal,  the  seam  is  usually  underlaid 
~by  clay. 

Kinds  of  Ore, — The  form  of  iron-ore  found  in  all  strata,  except  those 
containing  coal,  is  usually  ferric  oxide,  either  hydrated  (brown  .hema- 
tite— limonite),  or  anhydrous  (red  hematite),  or  else  magnetic  oxide ; 
but  in  the  Coal-measures  of  this  period,  and  in  the  Coal-measures  of 
every  other  period — i.  e.,  in  all  strata  containing  coal — the  iron  is  in 
the  form  of  ferrous  carbonate.  This  is  usually  mixed  with  clay,  and 
therefore  called  clay  iron-stone.  It  is  often  nodular  and  mammillated, 
and  called  kidney  iron-ore.  Sometimes  it  is  mixed  intimately  with  car- 
bonaceous matter,  and  is  called  black-band  ore.  This  last  very  valuable 
ore  is  found  in  Pennsylvania,  Ohio,  and  in  Scotland. 

The  importance  of  the  association  of  coal  and  iron  in  the  same 
strata  can  not  be  overestimated.  For  this  reason,  the  raising  of  coal 
and  the  manufacture  of  iron  are  conducted  in  connection  with  each 
other,  and  the  smelting-f urnaces  are  often  situated  at  the  mouths  of 
the  coal-mines.  It  is  easy  to  understand,  therefore,  why  Great  Britain, 
the  greatest  coal-producing  country  in  the  world,  should  be  also  the 
greatest  iron-producing  country.  Nearly  all  the  iron-ore  worked  in 
Great  Britain  is  taken  from  her  coal-measures.  In  this  country,  much 
iron  is  made  from  the  iron  carbonates  of  the  coal-measures,  but  much 
also  from  the  peroxide  and  magnetic  ores  found  elsewhere,  especially 
in  Laurentian  strata  (p.  286). 

The  following  table  gives  a  comparative  view  of  the  annual  iron- 
production,  in  tons,  of  the  principal  iron-producing  countries  of  the 
world.  It  will  be  seen  that  Great  Britain  makes  more  than  a  third  of 
the  iron  of  the  world.  The  rapid  increase  in  the  production  of  this 
great  agent  of  civilization  is  also  seen.  In  1888  the  iron  and  steel  pro- 
duction of  the  United  States  reached  the  enormous  amount  of  12,000,- 
000  tons: 


384: 


PALAEOZOIC  SYSTEM   OF  ROCKS. 


IRON  AND  STEEL. 

1845. 

1856. 

1864. 

1871. 

1878. 

.   1884. 

Great  Britain  
United  States  

2,200,000 
502,000 

3,500,000 
1,000,000 

5,000,000 
1,200,000 

5,667,000 

6,566,000 
2  560  000 

10,600,000 
6  200  000 

France  

450,000 

1,217,000 

1,381,000 

2,600  000 

Germany  

1  664  000 

4  500  000 

World  

7  000  000 

14  485  000 

27  300  000 

Theory  of  the  Accumulation  of  the  Iron-Ore  of  the  Coal-Measures.— 
We  have  already  explained  (p.  144)  how  iron-ore  is  now  accumulated 
by  the  agency  of  decaying  organic  matter.  We  have  also  shown  that 
if  the  organic  matter  is  consumed  in  doing  the  work  of  accumulation, 
the  iron-ore  is  left  in  the  form  of  iron  peroxide ;  but  if  it  is  accumu- 
lated in  the  presence  of  excess  of  organic  matter,  it  retains  the  form 
of  ferrous  carbonate.  We  will  now  give  additional  evidence,  taken 
from  the  occurrence  of  iron-ore  in  the  strata  of  the  earth,  that  the 
same  agency  has  accomplished  the  same  results  in  all  geological  times : 

1.  Immense  beds  of  iron-ore  are  found  in  the  strata  of  all  geological 
ages  ;  but,  wherever  we  find  them,  we  find  also  associated  a  correspond- 
ing amount  of  strata,  decolorized  or  leached  of  their  iron  coloring-mat- 
ter.    Contrarily,  wherever  we  find  the  rocks  extensively  red,  we  usually 
find  also  an  absence  of  valuable  beds  of  iron-ore.  (We  are  thus  led  to 
conclude  that  the  iron-ore  of  iron-beds  has  been  washed  out  of  the 
strata,  which  are  thereby  left  in  a  decolorized  condition?) 

2.  That  (this  has  been  done  by  the  agency  of  organic  matters  shown 
by  the  fact  that,  wherever  we  find  evidences  of  organic  matter,  whether 
in  the  form  of  fossils  or  of  coal,  we  find  the  sandstones  and  shales  are 
white  or  gray — i.  e.,  leached  of  coloring-matter.     Conversely,  red  rocks 
are  usually  barren  of  fossils  or  of  coal.     For  example,  all  the  sand- 
stones of  the  coal-measures,  or  of  all  other  strata  containing  coal,  are 
gray,  while  the  Old  Eed  sandstone  below  the  coal,  and  the  New  Eed 
sandstone  above  the  coal,  and,  in  fact;  all  red  sandstones,  are  very  poor 
in  fossils  or  evidences  of  organic  matter  of  any  kind.     Thus,  evidences 
of  organic  matter,  and  the  decoloring  of  the  strata,  and  the  accumula- 
tion of  iron-ore,  are  closely  associated  as  cause  and  effect. 

3.  In  all  the  strata,  whether  older  or  newer,  in  which  there  is.no 
coal,  i.  e.,  in  which  there  is  no  excess  of  organic  matter  in  a  state  of 
change,  the  iron-ore  is  peroxide \(  ferric  and  magnetic  oxide) ;  while  in 
coal-measures  of  all  periods,  whether  Carboniferous,  or  Jurassic,  or  Cre- 
taceous, or  Tertiary,  or  in  all  cases  where  there  is  organic  matter  in  ex- 
cess in  a  state  of  change  (not  graphite),  the  iron-ore  is  in  the  form  of 
carbonate  protoxide,  or  ferrous  carbonate  (FeC09). 

Therefore,  we  conclude  that  both  now  and  always  iron-ore  is,  and 
has  been,  accumulated  by  organic  agency ;  again,  that  both  now  and 
always  there  are,  and  have  been,  three  conditions  of  iron-ore,  each  as- 


IRON-ORE  OF  THE  COAL-MEASURES.  385 

sociated  with  the  absence  or  presence  in  smaller  or  larger  quantities  of 
changing  organic  matter :  1.  It  may  be  universally  diffused  as  a  color- 
ing-matter of  rocks  and  soils,  and  unavailable  for  industries ;  in  this 
case  there  has  been  no  organic  matter  to  leach  it  out  and  accumulate  it. 
2.  It  may  be  accumulated  as  ferric  oxide ;  in  this  case  there  has  been 
organic  matter  only  sufficient  to  do  the  work  of  accumulation,  and  was 
all  consumed  in  doing  that  work.  3.  It  may  be  accumulated  as  ferrous 
carbonate ;  in  this  case  there  is  excess  of  organic  matter,  usually  in  the 
form  of  coal. 

This  much  is  certain ;  but,  as  to  the  exact  mode  and  time  of  the 
leaching  and  accumulation,  there  is  some  difference  of  opinion.  There 
are  two  ways  in  which  the  accumulation  may  have  occurred :  It  may 
have(accumulated  in  the  coal-marshes  during  the  Coal  period,  being  at 
that  time  leached  out  of  the  surrounding  soils>  which  were  therefore 
left  in  a  decolorized  condition,  and  in  this  condition  subsequently  washed 
down  as  sediments  into  the  coal-marshes.  Or,  it  may  have  been  brought 
down  as  the  coloring-matter  of  red  sands  and  clays ;  and  afterward, 
perhaps  after  the  Coal  period,  leached  out  by  percolating  waters  con- 
taining organic  matter  from  the  coal-beds,  carried  downward  until 
stopped  by  an  impervious  clay-stratum,  and  accumulated  there.  The 
former  mode  is  the  more  probable.* 

But,  in  any  case,  organic  matter  has  been  the  agent ;  and,  there- 
fore, in  this  case,  as  in  all  other  cases,  iron-ore  is  the  sign  of  organic 
matter,  and  the  measure  of  the  amount  of  organic  matter  consumed  in 
its  accumulation.  There  are,  therefore,  three  signs  of  the  previous 
existence  of  organisms  used  by  geologists ;  they  are  coal,  iron-ore,  and 
fossils. 

We  can  not  dismiss  this  subject  without  making  one  passing  reflec- 
tion suggested  by  the  mention  of  these  three  signs  of  life  : 

The  organic  kingdom  is  so  much  matter  taken  from  the  atmosphere, 
embodied  for  a  brief  space  in  individual  living  forms,  to  be  again  dis- 
solved by  death,  and  returned  to  the  atmosphere  whence  it  came.  The 
same  material  is  again  taken  by  the  next  generation,  embodied  and 
again  returned  at  its  death.  The  same  small  quantity  of  matter  in  the 
atmosphere  is  embodied  and  disembodied,  again  embodied  and  disem- 
bodied, and  thus  worked  over  and  over  again  by  constant  circulation 
thousands,  yea,  millions  of  times,  in  the  history  of  the  earth.  Now,  in 
this  constant  circulation  of  the  elements  of  organic  matter,  besides  the 
work  done  in  the  fact  of  circulation  itself,  viz.,  the  wonderful  but  fleet- 
ing phenomena  of  vegetable,  animal,  yea,  of  human  life,  there  was  an- 
other work,  the  results  of  which  accumulated  from  age  to  age — a  work, 
too,  of  the  greatest  importance  to  the  well-being  of  the  human  race. 

*  Bischoff,  Chemical  Geology,  vol.  i,  p.  315. 
25 


386  PALAEOZOIC  SYSTEM  OF  ROCKS. 

A  portion  of  this  circulating  matter,  in  its  course  downward  from  the 
organic  to  the  mineral  kingdom,  stopped  half-way,  and  was  accumulated 
as  great  beds  of  coal — reservoirs  of  stored  force.  As  circulating  water 
descending  seaward  is  stopped  and  stored  in  reservoirs  to  complete  its 
descent  under  the  control  of  man,  and  do  his  work ;  so  circulating  or- 
ganic matter  descending  is  stopped  and  stored,  and  is  now  completing 
its  descent  under  the  control  of  man,  and  doing  his  work,  and  thus 
becomes  the  great  agent  of  modern  civilization. 

A  second  portion  of  circulating  organic  elements  completes  its  de- 
scent, but  in  doing  so  accumulates  iron-ore,  the  second  great  civilizer 
of  the  human  race. 

A  third  portion  also  completes  its  descent,  but  accumulates  neither 
coal  nor  iron-ore ;  but  it  accomplishes  a  work  far  more  subtile  and 
beautiful  than  either  of  the  others.  As  each  particle  of  organic  matter 
returns  to  the  atmosphere,  it  compels  a  particle  of  mineral  matter  to 
take  its  place,  thus  completely  reproducing  its  form  and  structure. 
Thus  fossils  are  formed,  and  thus  is  the  history  of  the  organic  kingdom 
self -recorded.  Thus,  while  the  other  two  portions  have  subserved  the 
material  wants  of  man,  this  portion  has  subserved  his  higher  intellect- 
ual wants. 

Bitumen,  Petroleum,  and  Natural  Gas. 

The  origin  of  bitumen  and  petroleum  is  so  closely  connected  with 
that  of  coal,  that  although  not  confined  to,  nor  even  found  principally 
in,  the  Coal-measures,  the  subject  is  best  taken  up  in  this  connection. 

It  is  well  known  that  coal  or  any  organic  matter,  by  suitable  distil- 
lation, may  be  broken  up  into  a  great  variety  of  products :  some  solid, 
as  coal-pitch ;  some  tarry,  as  coal-tar ;  some  liquid,  as  coal-oil ;  some 
volatile,  as  coal-naphtha;  and  some  gaseous,  as  coal-gas.  Now,  we  find 
collected,  in  fissures  beneath  the  earth,  or  issuing  from  its  surface,  a 
very  similar  series  of  products :  some  solid,  as  asphalt ;  some  tarry,  as 
litumen  ;  some  liquid,  as  petroleum  ;  some  volatile,  as  rock-naphtha  ; 
and  some  gaseous,  as  marsh-gas  of  burning  springs.  There  can  be  no 
doubt  that  these  also  are  of  organic  origin.  The  utilization  of  all 
these  products,  especially  petroleum  and  gas,  have  now  become  a  great 
industry. 

Geological  Relations. — Bitumen  and  petroleum  are  found  in  all  fos- 
siliferous  rocks,,  from  the  lowest  Silurian  to  the  uppermost  Tertiary, 
under  certain  conditions,  among  which  are  the  local  abundance  of  or- 
ganisms from  which  these  substances  are  formed,  and  the  absence  of 
great  metamorphism.  The  signs  of  their  presence  in  any  locality  are 
iridescent  scums  on  the  water  of  springs  (oil-show),  and  the  issuing  of 
combustible  gases  (burning  springs).  In  regard  to  the  first  sign,  it 
must  be  remembered  that  iridescent  scums  are  produced  by  many  other 
substances  besides  petroleum.  The  second  sign  is  considered  the  best, 


BITUMEN,  PETROLEUM,  AND   NATURAL   GAS. 


387 


although  combustible  gases  may  issue  from  decomposing  organic  matter 
of  any  kind,  or  from  coal.  Some  of  the  burning  springs  in  the  oil- 
region  of  Kentucky  are  said  to  produce  a  flame  twenty  to  thirty  feet 
long.  It  is  a  significant  fact  that  petroleum  is  often  associated  with 
salt.  It  is  so  in  Pennsylvania,  in  Virginia,  and  in  many  other  localities. 

Oil-Formations. — I  have  said  that  petroleum  and  bitumen  are  found 
in  all  fossiliferous  formations,  but  in  each  country  there  are  certain  for- 
mations where  it  especially  abounds :  in  Europe  it  is  found  principally 
in  the  Tertiary ;  in  Eastern  United  States  it  is  found  almost  wholly  in 
the  Palaeozoic,  below  the  Coal-measures ;  in  California  it  is  found  in  the 
Tertiary. 

Principal  Oil-Horizons  of  the  United  States. — In  Pennsylvania  and 
Kentucky  oil  is  found  in  the  Upper  Devonian ;  in  Canada  and  Michigan, 
in  the  Lower  Devonian ;  in  Western  Virginia  it  is  found  in  the  sub- 
Carboniferous  ;  in  Ohio,  in  Lower  Coal-measures,  in  the  Upper  De- 
vonian (Huron  shales),  and  even  in  the  Lower  Silurian  (Trenton  lime- 
stone) ;  in  California  it  is  found  in  the  Miocene  Tertiary  of  the  Coast 
Range,  all  the  way  from  Los  Angeles  to  Cape  Mendocino.  These  have 
been  called  oil-horizons. 

Laws  of  Interior  Distribution. — The  mode  of  interior  distribution 
of  petroleum  and  bitumen  is  similar  to,  yet  different  from,  that  of 
water.  Like  water,  it  occurs  in  porous  strata  and  collected  in  fissures 
and  cavities ;  like  water  and  with  water,  it  issues  in  hill-side  springs ; 
like  water  and  with  water,  it  collects  in  ordinary  wells,  or  sometimes 
spouts  in  immense  quantities  from  artesian  wells.  Some  of  the  great 
spouting-wells  of  Pennsylvania,  when  first  opened,  yielded  3,000  barrels, 
some  in  Ohio  5,000  barrels, 

and  some  of  the  great  wells    s  p     ^        «^  $ 

of  Baku,  on  the  borders  of  the 
Caspian  Sea,  even  1,000,000 
gallons  per  day.  But,  unlike 
water,  there  is  no  perennial 
large  supply  ;  the  accumula- 
tions of  ages  being  exhausted 
in  a  few  months  or  a  few 
years.  Unlike  water,  the  force 
of  ejection  in  great  spouting- 
wells  is  not  hydrostatic  press- 
ure directly,  but  the  pressure  of  elastic  gases  generated  from  the  petro- 
leum ;  though,  as  Orton  has  shown,  the  elastic  compression  of  these  is 
probably  due  to  hydrostatic  pressure.  The  great  scouting -ivells,  being, 
therefore,  the  fortunate  tappings  of  reservoirs  which  have  been  accumu- 
lating for  millenniums  in  great  fissures  and  cavities,  are  enormously 
productive,  but  also  rapidly  exhausted.  It  is  evident  that  the  same  is 


FIG.  517. 


388 


PALEOZOIC   SYSTEM   OF  ROCKS. 


much  more  true  of  gas- wells ;  they  must  be  very  short-lived.  In  the 
case  of  less  productive  but  more  permanent  wells,  the  oil  is  contained 
in  more  numerous  but  smaller  fissures  and  pores.  In  all  cases  of  col- 
lection in  large  fissures  and  cavities,  these  reservoirs  are  occupied  also 
by  water  and  gas ;  and  the  three  materials  arrange  themselves  in  the 
order  of  their  relative  specific  gravities,  as  in  Figs.  517  and  518. 

These  facts  easily  account  for  the  many  curious  phenomena  con- 
nected with  oil-wells.     Thus,  if  the  well  a  (Fig.  517)  taps  the  reser- 
voir, only  gas  will  escape,  and  oil 
and  water   can  be  got  only  by 
pump.     But  if  the  well  be  at  #, 
oil   will   spout ;  and   afterward, 
when   the  gas  has  escaped,  oil 
and  water  may  be  pumped.     If 
the  well  be  at  c,  then  water  will 
spout  first  and  afterward  oil.     If 
the    cavity    be    irregular,    with 
more  than  one  chamber  contain- 
ing compressed  gas  (Fig.  518), 
and  the  well  be  at  «,  then  gas  will  escape  first,  and  afterward  oil  and 
water  will  spout. 

Kinds  of  Rocks  which  bear  Petroleum. — As  already  stated,  petro- 
leum, like  water,  is  found  principally  in  pores  and  fissures  and  cavities. 
The  same  kinds  of  rocks,  therefore,  which  are  water-bearing  are  also 
oil-bearing,  viz.,  limestones  and  sandstones.  In  Canada  it  is  found  in 
limestone,  in  Pennsylvania  in  sandstone.  The  intervening  shales  are 
usually  barren.  In  Pennsylvania  there  are  three  oil-bearing  sandstones, 
separated  by  about  200  feet  of  intervening  shales.  If  a  well  reaches 
the  first  sandstone  without  obtaining  oil,  the  boring  is  continued  to 
the  second,  or  even  to  the  third.  Fig.  519  (taken  from  Lesley)  rep- 
resents a  section  through  the  Pennsylvania  oil-regions,  showing  the 

OIL    CR 


FIG.  518. 


three  principal  oil-horizons  of  the  United  States,  viz.,  the  Venango 
County  (Pennsylvania)  horizon  with  its  three  sandstones ;  the  Virginia 
sub- Carboniferous  horizon  above  ;  and  the  Canada  horizon  below. 

Petroleum  (especially  the  lighter  oils)  is  usually  found  only  in  hori- 
zontal or  gently-folded  strata,  because  strongly-folded  and  crumpled 
strata  are  always  metamorphic,  and  the  heat  which  produced  meta- 
morphism  has  also  concreted  the  oil  into  bitumen  or  asphalt.  Also  the 
outcropping  of  the  edges  of  highly-inclined  strata  favors  the  escape  of 


ORIGIN   OF   PETROLEUM   AND  BITUMEN.  389 


gas    and  the  concretion  of  the  oil.     It  is  hardly  probable,  therefore 
that  a  light  oil  will  ever  be  found  in  the  California  oil-region.* 

In  gently-folded  strata  the  most  productive  portions  seem  to  be 
along  a  line  of  anticline ;  because  there  we  may  expect  large  fissures, 
and  also,  perhaps,  because  the  oil  working  up  on  the  surface  of  water, 
is  apt  to  accumulate  under  the  saddles  of  the  strata. 

Origin  of  Petroleum  and  Bitumen. 

We  have  seen  that  the  whole  petroleum  and  bitumen  series  may  be 
made  artificially  by  destructive  distillation  of  coal.  There  seems  also 
to  be  little  doubt  that  certain  organic  matters  at  ordinary  temperature, 
in  presence  of  abundant  moisture,  and  out  of  contact  of  air,  will  un- 
dergo a  species  of  decomposition  or  fermentation  by  which  an  oily  or 
tarry  substance,  similar  to  bitumen,  is  formed.  In  the  interior  of  heaps 
of  vegetable  substance  such  bituminous  matter  is  often  found. 

There  are  therefore  two  general  theories  of  the  origin  of  petroleum  : 
one,  that  it  is  produced  by  the  distillation  at  high  temperature  of  bitu- 
minous coal  by  volcanic  heat,  the  coal  being  left  as  anthracite ;  the 
other,  that  it  is  formed  at  ordinary  temperature  by  a  peculiar  decompo- 
sition of  certain  organic  matters.  The  evidence  in  favor  of  the  first 
view  is  the  similarity  between  the  artificial  and  the  natural  series ;  the 
objection  to  it  is  that  the  occurrence  of  petroleum  seems  to  have  no 
necessary  connection  with  the  occurrence  below  of  coal-seams,  and  also 
that  petroleum  is  found  mostly  in  strata  which  have  not  been  subjected 
to  any  considerable  heat. 

The  argument  for  the  other-  view  is  the  fact  that  we  actually  find 
fossil  cavities  in  solid  limestone  containing  bitumen,  evidently  formed 
by  decomposition  of  the  animal  matter.  So,  also,  shales  have  been 
found  in  Scotland  filled  with  fishes,  which  have  changed  into  bitumen. 

The  most  probable  view  seems  to  be  that  both  coal  and  petroleum 
are  formed  from  organic  matter,  but  of  different  kinds  and  under 
slightly  different  conditions — that  coal  is  formed  from  terrestrial  vas- 
cular plants,  in  the  presence  of  fresh  water,  while  bitumen  and  petro- 
leum are  formed  from  more  perishable  cellular  plants  and  animals,  in 
the  presence  of  salt-water.  We  have  already  noticed  the  frequent  asso- 
ciation of  petroleum  and  salt.f 

According  to  this  view,  taking  the  composition  of  petroleum  as 
CnH2ll-|-2,  the  reaction  by  which  it  is  formed  from  vegetable  matter  is 
expressed  in  the  following : 

*  Some  tolerably  good  oil  has  been  found  in  California  in  metamorphic  strata. 

f  Recently  the  chemist  Mendeljeff  has  revived  the  theory  of  the  mineral  origin  of 
petroleum.  According  to  him,  it  is  probably  made  by  reaction  at  high  temperatures  of 
vapor  of  water  (HaO)  on  carbide  of  iron  (F2C).  It  is  hardly  probable  that  geologists 
will  accept  this  view. 


390  PALEOZOIC   SYSTEM  OF  ROCKS. 


Cellulose  .................................  C98H6o080 


Subtract 


And  there  remains  .........................  Ci3H28  =  petroleum. 

Origin  of  Varieties.  —  However  formed,  there  can  be  no  doubt  that 
the  different  varieties  of  this  series  are  formed  from  one  another  by  a 
subsequent  process.  It  is  certain  that  from  all  varieties  CH4  is  con- 
stantly passing  off,  and  that  the  result  of  this  is  a  slow  consolidation. 
By  this  process  light  oil  is  changed  into  heavy  oil,  heavy  oil  into  bitu- 
men, and  bitumen  into  asphalt.  Some  of  the  grandest  fissure-reservoirs 
of  oil  have  thus  been  changed  into  solid  asphalt.  In  the  upper  barren 
Coal-measures  of  West  Virginia  there  is  a  vein  of  asphalt  four  feet 
thick,  over  3,000  feet  long,  and  of  unknown  depth.  It  fills  a  great 
fissure  which  breaks  through  the  rocks  nearly  perpendicularly,  and  out- 
crops on  the  surface. 

There  are,  therefore,  two  series  of  substances  formed  from  organic 
matter,  viz.,  the  coal  series  and  the  oil  series.  In  each  series  the  pro- 
portion of  carbon  increases  by  subsequent  change  until,  perhaps,  pure 
carbon  may  be  reached.  In  the  coal  series  we  have  fat  coal,  bitumi- 
nous coal,  semi-anthracite,  anthracite,  and,  finally,  graphite.  In  the  oil 
series  we  have  light  oil,  heavy  oil,  bitumen,  asphalt,  probably  jet,  and 
possibly,  finally,  diamond:  for  Liebig  has  suggested  that  diamond  is 
most  probably  formed  by  crystallization  of  carbon  from  a  liquid  hydro- 
carbon, in  which  the  proportion  of  carbon  is  constantly  increasing  by 
loss  of  CH4.* 

Future  of  this  Industry.  —  The  oil  in  the  United  States  is  practically 
inexhaustible.  The  finding  of  great  reservoirs,  producing  spouting- 
wells,  has  always  been,  and  always  will  be,  very  uncertain,  and  the 
duration  of  their  productiveness  limited  ;  but  a  moderate  return  for 
industry  and  capital  is  certain  for  an  almost  unlimited  time.  A  large 
portion  of  the  Palaeozoic  basin,  including  an  area  of  about  200,000 
square  miles,  is  underlaid  by  rocks  which  are  more  or  less  oil-bearing. 
The  eastern  portion  of  the  United  States  is  the  great  oil-bearing,  as  it 
is  the  great  coal-bearing,  country  of  the  world.  The  gas  supply  will 
probably  be  much  more  quickly  exhausted. 

Fauna  of  the  Carboniferous  Age. 

As  heretofore,  we  will  disregard  the  subdivisions,  and  treat  of  the 
fauna  of  the  whole  age,  or  at  least  the  two  periods  sub-Carboniferous 
and  Carboniferous,  together.  It  must  be  borne  in  mind,  however,  that 
most  of  the  lower  marine  animals  mentioned  are  from  the  sub-  Carbon- 

/• 

*  This  view  seems  to  be  confirmed  by  recent  observations  in  South  Africa  and  South 
America.  Lewis,  Science,  vol.  viii,  p.  345  ;  Derby,  Science,  vol.  ix,  p.  57. 


FAUNA   OF  THE   CARBONIFEROUS  AGE. 


391 


iferous,  while  most  of  the  fresh- water  and  la  ad  animals  are  from  the 
Coal-measures.     We  can  notice  only  what  important  families  are  going 


FIG.  520.  FIG.  522. 

FIGS.  520-522.— CARBONIFEROUS  CORALS:  520.  Lithostrotion  Cal if orniense  (after  Meek).  521.  Cli- 
giophyllum  Gabbi  (after  Meek).  522.  a,  Archimedes  Wortheni  (after  Hall);  b,  portion  of  same, 
enlarged  to  show  structure. 

out,  what  important  families  are  coming  in,  and  a  few  which  are  very 
characteristic.  We  shall  dwell  only  on  what  bears  on  the  progress  of 
life. 

Among  corals  the  same  general  characteristic  Palaeozoic  type  (Quad- 
ripartita)  continues  to  prevail,  though  in  greatly-diminished  variety 
of  families ;  for  the  Favositidae  and  Halysitidas  have  passed  away,  and 
only  the  Cyathophylloids,  or  cup-corals,  remain.  The  most  beautiful 
and  characteristic  are  the  Columnar  Lithostrotion  (Fig.  520),  a  polyp- 
coral,  and  the  curious  corkscrew-like  Archimedes  (Fig.  522),  a  Bryozoan. 

Among  Crinoids,  the  Cystids  no  longer  exist,  for  they  passed  out 
with  the  Silurian,  but  the  Blastoids  and  Crinids  (Figs.  523-530)  in- 
crease in  number  and  beauty.  Also  among  free  Echinoderms  the  As- 
teroids (Fig.  533)  are  more  abundant,  and  Echinoids  (Figs.  531  and 
532)  are  introduced  for  the  first  time.  Fig.  534  represents  the  distri- 
bution of  these  orders  in  time. 


392 


PALAEOZOIC  SYSTEM  OF  ROCKS. 


Among  Brachiopods,  the  straight-hinged  or  square-shouldered  kinds 
continue,  but  pass  out  almost  wholly  with  this  age. 


Fm.  527. 


FIG.  529. 


FIG.  528. 


FIGS.  523-529.— ECHINODERMS  or  THE  CARBONIFEROUS  AGU—Blastoids  ;  523.  Pentremites  Bnrling- 
toniensis  (after  Meek).  524.  Pentremites  gracilis  (after  Meek).  525.  Pentremites  cervinus  (after 
Hall).  526.  Pentremites  pyriformis  (after  Hall).  526a.  Pentremite  restored  (after  Lutken). 
Crinids:  527.  Batocrinus  Chrystii  (after  Meek).  528.  Scaphiocrinus  scalaris  (after  Meek).  529. 
Forbesiocrinus  Wortheni  (after  Meek). 

Land  and  fresh-water  shells,  as  might  have  been  expected,  are  be- 
ginning to  be  found  in  great  abundance  in  the  Coal-measures.  The 
genus  Pupa,  a  land  air-breathing  gasteropod,  and  the  genus  Cyclas,  a 
fresh-water  bivalve,  and  the  genus  Cypris,  a  little  crustacean  bivalve, 
all  of  which  are  still  represented  by  living  species,  are  found.  . 

Of  course,  marine  species,  both  Lamellibranchs  and  Gasteropods, 
are  abundant.  Some  figures  of  these  are  given  below. 

Among  Cephalopods,  Orthoceratites  still  continue,  but  in  diminished 
number,  variety,  and  size.  Goniatites,  introduced  in  the  Devonian, 


FAUNA  OF  THE  CARBONIFEROUS  AGE. 


393 


FIG.  532  b. 


^Sfer* 
!4H&£T*> 

•--/^'v, 

^1^.  *rr* 

^  FIG.  533. 

FIG.  532  a. 

FIGS.  530-533.— ECHINODERMB  or  THE  CARBONWEROUS  AGE—  Crinid:  530.  Zeacrinns  elegans  (after 
Hall).  Echinoids  and  Asteroids  ;  531.  Oligoporus  nobilis,  x  A  (after  Meek).  532.  a,  Archaeoci- 
daris  Wortheni  (after  Hall);  b,  Spine  of  same,  natural  size.  533.  Ony chaster  flexihs (after  Meek). 

also  continue,  but  both  may  be  said  to  pass  out  with  this  age,  although 
a  few  seem  to  pass  into  the  Lower  Triassic. 


___—  PALAEOZOIC  - 

^~37z  urian         Devon  '-l       Carlo 


NEOZOIC 


STEM  M  ED 


FIG.  534.— Diagram  showing  General  Distribution  of  Echinoderms  in  Time:    Shaded  portion, 

stemmed;  unshaded,  free. 

Trilolites  and  Eurypterids  also  continue  ready  to  disappear  at  the 
end,  but  an  advance  in  the  Crustacean  class  is  observed  in  the  intro- 


394 


PALJEOZOIC  SYSTEM  OF  ROCKS. 
b 


FIG.  536. 


FIG.  538. 


FIG.  537. 

FIGS.  535-538. — CARBONIFEROUS  BRACHIOPODS:  535.  Spirifer  plenus  (after  Hall);  a,  dorsal  view:  b, 
side  view.  536.  Chonetes  Dalmaniana.  537.  Prodnctus  punctatus  (after  Meek).  538.  Produc- 
tns  mesialis  (after  Hall);  a,  ventral  view;  b,  side  view. 

duction  here  of  Limuloids  (king-crabs),  Fig.  555,  and  of  Macrourans 
—long- tailed  Crustaceans  (lobsters,  crawfish,  shrimps,  etc.),  Figs.  557 
and  559.  Here,  then,  we  have  two  important  steps  in  the  progress  of 


FIG.  539. 


FIG.  542. 


FIG.  544. 


FIGS.  539-544.  —  CARBONIFEROUS  LAND  AND  FRESH-WATER  SHELLS:  539.  Pupa  vetusta  (after  Daw- 
eon—  a  Land-Shell;  a,  natural  size;  b,  enlarged.  540.  Cypris  (after  Dawson);  a,  natural  size. 
541.  Spirorbis  (after  Dawson);  a,  natural  size.  542.  Naiadites  (after  Dawson).  543.  Dawson- 
ella  Meekii  (after  Bradley).  544.  Anthracopupa  Ohioensis  (after  Whitfield). 


FAUNA  OF  THE  CARBONIFEROUS   AGE. 


395 


life.  The  gradual  process  of  change  may  be  clearly  traced  in  the  one, 
but  not  yet  in  the  other.  Although  Limuloids  are  clearly  differen- 
tiated first  in  the  Carbon- 
iferous, yet  transition  forms 
may  be  traced  even  to  the 
Upper  Silurian.  If,  with 
Packard,  we  divide  Crusta- 
ceans into  two  groups — Pa- 
Iseo-carida  and  Neo-carida 
(old  style  and  new  style 
Crustaceans)  —  then  Trilo- 
bites,  Eurypterids,  and  Lim- 


FIG.  546. 


Fro.  547. 


FIGS.  545-548.— CARBONIFEROUS   LAMELLIBRANCHS  (after  Meek):  545.  Solenomya  anodontoides. 
546.  Allorisma  ventricosa.    547.  Allorisma  pleuropistha.    548.  Astartella  Newberryi. 

uloids,  belong  to  the  Palaeo-carida.     That  these  were  all  derived  from 
the  Trilobite  is  shown  by  the  transition  forms  561  a  and  £,  which  must 


FIG.  549. 


FIG.  550. 


FIG.  552. 


FIG.  551. 


FIGS.  549-552.— CARBONIFEROUS  GASTEROPODS  (after  Meek):  549.  Macrocheilns  Newberryi.    550. 
Pleurotomaria  scitula.    551.  Euomphalus  subquadratus.    552.  Bellerophon  sublsevis  (after  Hall.) 

b 


FIG  553. 


FIG.  554. 


FIGS.  553,  554.— CARBONIFEROUS  GONIATITES:  553.  Goniatites  Lyoni  (after  Meek);  a,  side  view; 
b,  end  view.    554.  Goniatites  crenistria  (European);  a,  side  view;  b,  end  view. 


396 


PALAEOZOIC  SYSTEM  OF  ROCKS. 


FIG.  557. 


FIG.  558. 


FIG.  559. 


FIGS.  555-559. — CARBONIFEROUS  CRUSTACEANS:  555.  EnproOps  Danae  (after  Meek  and  Worthen). 
556.  Phillipsia  Lodiensis  (after  Meek).  557.  Acanthotelson  Stimpsoni  restored  (after  Packard). 
558.  Palaeocarus  typus  (after  Meek  and  Worthen).  559.  Anthrapalaemon  gracilis  (after  Meek 
and  Worthen). 

be  compared  with  figures  of  Trilobites  and  Limulus  previously  given. 
As  already  seen  (p.  335),  the  same  view  is  confirmed  by  embryology. 


FIG.  560.— a,  Palseoniscus  aculeatus  (after  Nieskowski)  :  a  Enrypterid  from  Upper  Silurian, 
olimulus  f alcatus  (after  Woodward) :  a  Limuloid  from  Upper  Silurian. 


6.Ne- 


FAUNA   OF   THE   CARBONIFEROUS  AGE. 


397 


The  genesis  of  the  Neo-carida  we  do  not  know.  They  certainly  did  not 
come  from  the  Palaeo-carida,  but  possibly  from  some  early  and  low  form 
of  Crustaceans  like  Hymenocarus  (Fig.  287,  p.  300). 

Insects  now,  for  the  first  time,  appear  in  considerable  numbers  and 
variety.     As  might  be  expected,  these  are  associated  with  the  abundant 


PIG.  566. 

PIGS.  561-566.— CARBONIFEROUS  INSECTS:  561.  a,  Eoscorpins  carbonarins  (after  Meek  and  Wor- 
then).  b,  Anthrolycosa  antlqua  (after  Beccher).  '  562.  Blatta  Helvetica,  x  f,  restored  (after 
Heer).  563.  Miamia  Danse  (after  Scudder).  564.  Euphoberia  armigera  (after  Meek  and  Worthen). 
565.  Zylobius  .sigillarise  (after  Dawson).  a,  Anterior  portion  enlarged.  666.  Corydaloides  Scud- 
deri,  x  |  (after  Brogniart). 


398 


PALAEOZOIC   SYSTEM   OF  ROCKS. 


land  vegetation  of  the  Coal.  Many  of  the  principal  orders  are  here 
represented,  viz.,  Dragon- flies  (Neuropters),  Figs.  563  and  566 ;  grass- 
hoppers and  cockroaches  (Orthopters),  Fig.  562 ;  spiders  and  scorpions 
(Arachnids),  Figs.  561  a  and  561  1} ;  and  centipeds  (Myriapods),  Figs. 
565  and  565  a.  It  is  noteworthy,  however,  that  the  three  highest  or- 
ders, viz.,  the  butterflies  (Lepidopters),  the  social  insects,  such  as  bees, 
ants,  etc.  (Hymeiiopters),  and  the  flies  (Dipters),  are  still  wanting. 
These  are  not  only  the  highest  but  also  the  flower-loving,  honey-suck- 
ing orders.  True  flowering  plants  (Angiosperms)  did  not  yet  exist. 
Beauty  and  fragrance  and  sweetness  were  not  yet  characteristic  of  the 
reproduction  of  plants. 

Eecently  immense  numbers  of  Carboniferous  insects  have  been 
found  at  Commentry  and  described  by  Brogniart.  Among  these  are  the 
largest  insects  known.  One — a  phasma  (Fig.  566) — was  about  a  foot 
long  and  twenty-six  or  twenty-eight  inches  across  the  extended  wings. 
As  already  said  (p.  334),  all  the  Palaeozoic  hexapod  insects  belong  to 
one  order — the  Palceo-dictyoptera  of  Scudder — a  generalized  type,  con- 
necting the  three  lower  orders — Neuropters,  Orthopters,  and  Hemipters 
— of  existing  insects ;  some  approaching  one  arid  some  another  of  these 
now  widely  separated  orders.  . 

Vertebrates  (Fishes). — The  great  Ganoids  and  Placoids  continue  in 
undiminished  or  even  increased  numbers,  size,  and  variety.  They  are 


FIG.  568. 


FIG.  569. 


FIG.  570. 

FIGS.  567-570.— CAKBONIFEROUS  FISHES— Placoids :  567.  Edestes  minor  (after  Newberry).  568. 
Pleuracanthus— a  Ray  (after  Nicholson).  569.  Gyracanthus  (after  Nicholson).  570.  Ctenacan- 
thus  (after  Nicholson). 


FAUNA   OF  THE   CARBONIFEROUS   AGE. 


399 


FIG.  576. 


FIG.  575. 


FIGS.  571-576.—  CARBONIFEROUS  FISHES— Placoids :  571.  Cochliodns  contortns.  572.  Petalodas 
destructor  (after  Newberry).  573.  Cladodus  epinosus  (after  Newberry).  5T4.  Orodns  mamrai- 
lare  (after  Newberry).— Ganoids:  575.  Amblypterus  macropterus.  576.  Tooth  of  Holoptychius 
Hibberti,  natural  size. 

still  the  rulers  of  the  seas.  Of  Placoids,  one  has  been  found  with  dorsal 
spine  eighteen  inches  long,  another  with  spine  three  inches  broad  and 
nine  and  a  half  inches  long,  although  much  of  the  point  is  broken  off. 
Their  teeth,  too,  are  beginning  to  assume  more  of  the  character  of  true 
shark's- teeth.  They  are  no  longer  wholly  Cestracionts  (Fig.  571),  but 
also  now  Hybodonts,  having  teeth  somewhat  like  modern  sharks,  but 
rounded  on  the  edges  (Figs.  573  and  574).  Among  Ganoids^  the 
well-protected  but  sluggishly-moving  Placoderms  have  passed  away, 
but  the  Sauroids  continue  in  increased  numbers  and  size.  Bony,  en- 
ameled scales  of  the  Megalichthys  and  Holoptychius  are  found,  two  to 
three  inches  across;  and  jaws  of  the  Holoptychius,  a  foot  or  more 
long,  armed  with  Saurian  teeth,  two  inches  in  length  (Fig.  576).  Also, 


400 


PALAEOZOIC   SYSTEM   OF   ROCKS. 


as  we  approach  the  time  for  the  appearance  of  Reptiles,  some  of  these 
Sauroid  fishes  seem  to  become  still  more  reptilian  in  character,  while 
others  become  more  fish-like. 

Reptiles — Amphibians. — The  first  known  appearance  of  the  class  of 
Reptiles  on  the  earth  was  in  this  age  :  not  yet,  however,  in  as  great 
numbers  or  size,  or  as  high  in  the  scale  of  organization,  as  in  the  next 
age.  The  reign  of  Reptiles  had  not  yet  commenced. 

The  class  of  Reptiles  may  be  divided  into  two  sub-classes,  viz.,  True 
Reptiles  and  Amphibians.  The  Amphibians  differ  so  greatly  from 
other  Reptiles  that  they  are  now  usually  made  a  distinct  class,  inter- 
mediate between  Fishes  and  True  Reptiles.  Of  these  two  sub-classes 
only  the  Amphibians  are  certainly  known  to  have  been  represented  in 
the  Carboniferous.  Again,  Amphibians  are  subdivided  into  four  or- 
ders, viz. :  1.  Tailless  Amphibians  (Anoura),  such  as  frogs,  toads,  etc. ; 
2.  Tailed  Amphibians  ( Urodeld),  such  as  tritons,  salamanders,  sirens, 
etc. ;  3.  The  rare  snake-like  forms  ( Opliiomorplia  or  Gymnopliiona) ;  and 
4.  Labyrinthodonts.  Of  the'se,  only  the  Labyrinthodonts  were  repre- 
sented in  the  Carboniferous.  The  other  three  orders  still  exist,  but 
the  last  has  been  long  extinct.  The  Labyrinthodonts  were  very  large, 
often  gigantic  reptiles.  They  were  most  of  them  salamandriform,  with 
long  tail,  weak  limbs,  and  sluggish  movement.  Some  were  pisciform, 
and  had  paddles  instead  of  feet. 

We  can  only  briefly  describe  a  few  representatives  of  the  class,  and 
draw  some  conclusions. 

1.  Reptilian  Footprints. — In  the  sub-Carboniferous  of  Pennsylvania, 
near  Pottsville,  have  been  found  tracks  of  a  four-footed,  crawling  ani- 
mal (Sauropus  primwvus),  having  thick,  fleshy  feet  about  four  inches 
long,  and  making  a  stride  of  about  thirteen  inches.  The  impression  of 


FIG.  577.— Fossil  Rain-prints  of  the  Coal  Period. 

a  dragging  tail  is  also  visible.     The  surface  of  the  slab  on  which  the 
tracks  are  found  is  marked  with  distinct  ripple-bars  and  rain-prints. 


FAUNA   OF  THE   CARBONIFEROUS  AGE. 


401 


"  We  thus  learn,"  says  Dana,  "  that  there  existed  in  the  region  about 
Pottsville,  at  that .  time,  a  mud-flat  on  the  border  of  a  Tx>dy  of  water ; 
that  the  flat  was  swept  by  wavelets,  leaving  ripple-marks ;  that  the  rip- 
ples were  still  fresh  when  a  large  amphibian  walked  across  the  place ; 
that  a  brief  show- 
er of  rain  follow- 
ed, dotting  with 
its  drops  the  half- 
dried  mud ;  that 
the  waters  again 
flowed  over  the 
flat,  making  new 
deposits  of  detri- 
tus, and  so  buried 
the  records."  This 
is  the  earliest 
knoivn  land -ver- 
tebrate. 

Similar  tracks 
have  also  been 
found  in  the  Coal- 
measures  of  Penn- 
sylvania, on  a  slab 
affected  with  sun- 
cracks  (Fig.  578). 
The  reptile  had 
evidently  walked 
on  the  cracked 
and  half  -  dried 
mud  at  low  tide. 
Tracks  have  also 
been  found  in  the 
Coal-measures  of 
Illinois,  Indiana, 

Kansas,  and  Nova  Scotia,  and  in  the  latter  region  beautiful  specimens 
of  rain-prints  (Fig.  577). 

There  can  be  little  doubt  that  the  reptiles  making  the  tracks  men- 
tioned above  were  Labyrinthodonts. 

2.  Dendrerpeton, — In  the  Coal-measures  of  Nova  Scotia  have  been 
found  quite  a  number  of  small  reptiles,  belonging  to  several  genera. 
Among  these  one  is  especially  interesting,  on  account  of  the  conditions 
under  which  it  seems  to  have  been  preserved.  It  is  called  the  Den- 
drerpeton— tree-reptile  (Fig.  579),  because  it  was  found  by  Dawson  and 
Lyell  in  sand-stone,  filling  the  hollow  stump  of  a  Sigillaria  (Fig.  580), 
26 


FIG.  578.— Slab  of  Sandstone  with  Reptilian  Footprints,  from  Coal-meas- 
ures of  Pennsylvania;  x  \. 


4:02 


PALAEOZOIC   SYSTEM   OF  ROCKS. 


along  with  another  small  species  of  reptile,  a  number  of  land-shells — 
pupa,  etc.  (Fig.  539,  p.  394),  and  a  myriapod  (Fig.  565,  p.  397).  The 
Sigillaria  possessed  a  thick,  strong  bark,  which  was  more  resistant  of  de- 
composition than  the  cellular  interior.  Stumps  of  these  trees  are  often 
found,  consisting  only  of  coaly  bark  filled  with  sandstone,  evidently  de- 


PIG.  579.— Jaw  of  Dendrerpeton  Acadeanum,  and  Section  of 
Tooth,  enlarged  (after  Dawson). 


FIG.  580.— Section  of  Hollow  Sigil- 
laria Stump,  filled  with  Sand- 
stone (after  Dawson). 


posited  within  the  hollow.  These  sands  are  rich  repositories  of  organic 
remains.  We  can  easily  imagine  the  circumstances  under  which  the 
Dendrerpeton  was  preserved.  A  dead  Sigillaria  tree,  rotted  to  the  base 
and  only  its  hollow  stump  remaining,  stood  on  the  margin  of  a  coal 
-swamp  ;  river-floods  filled  the  stump  with  sand ;  in  the  stump  lived  and 
perished  a  Dendrerpeton  ;  or  else,  more  probably,  the  dead  body  of  the 
reptile,  together  with  shells  and  other  organic  remains,  was  floated  into 
the  hollow  stump  and  buried  there.  This  reptile  was  probably  a  Labyrin- 
thodont,  but  with  strong  alliances  with  true  reptiles,  especially  Lacertians. 
3.  Archegosaums  (Primordial  Saurian). — In  the  Bavarian  Coal- 
measures  has  been  found  the  almost  perfect  skeleton  of  a  reptile,  about 
three  and  a  half  feet  long,  which  combines  in  a  remarkable  degree  the 
characters  of  Amphibians  with  those  of  Ganoid  Fishes.  It  seems  to 
have  been  a  Labyrinthodont  Amphibian,  with  general  form  and  struct- 
ure adapted  for  a  purely  aquatic  life.  It  had,  certainly  in  the  early 
stages  of  its  life,  probably  throughout  life,  both  gills  and  lungs,  and 
therefore,  like  all  the  Amphibians  of  the  present  day  at  this  stage,  or 
like  Perennibranchiate  Amphibians  throughout  life,  breathed  both  air 
and  water.  The  locomotive  organs  were  paddles,  adapted  for  swim- 
ming, not  for  walking.  The  body  was  covered  with  imbricated  ganoid 
scales  (Fig.  581,  A),  and  the  head  with  ganoid  plates.  The  structure 


FIG.  581.— Archegosaurus. 

of  the  teeth  (B]  was  also  ganoid.  The  bodies  of  the  vertebrae  were 
not  ossified  nor  even  cartilaginous,  but  retained  the  early  embryonic, 
fibrous  condition  of  a  notochord,  It  was  apparently  a  connecting  link 


FAUNA   OF   THE    CARBONIFEROUS   AGE. 


403 


between  the  lowest  Perennibranchiate  Amphibians  and  the  Sauroid 
Fishes  (Owen),  with,  perhaps,  some  alliances  with  the  marine  Saurians 
which  afterward  appeared.  It  was  so  distinct  from  other  Labyrintho- 
donts  that  Prof.  Owen  puts  it  in  a  distinct  order  which  he  calls  Gano- 
cephala.  The  skeleton  of  this  animal  is  given  above  (Fig.  581)  with 
the  limbs  (C  and  D)  and  jaw  (E)  of  a  Proteus — a  perennibranchiate 
amphibian — for  comparison. 

4.  Eosaurus. — In  the  Coal-measures  of  Nova  Scotia,  in  1861,  Prof. 
Marsh  found  the  vertebrae  of  what  he  thinks,  with  some  reason,  was  a 
marine  Saurian ;  an 
order  which  is  large- 
ly developed  in  the 
Mesozoic.  But  as 
only  the  bodies  of  a 
few  vertebrae  have 
been  found,  and  as 
the  bi-concavity  of 
these  is  the  chief 
evidence  of  marine 
Saurian  affinity  and 
as  bi-concavity  also 
exists  among  Laby- 
rinthodonts,  Huxley 
believes  this  was  also 
a  Labyrintho'dont.  There  is,  therefore,  still  some  doubt  as  to  the  true 
affinity  of  this  animal.  The  size  of  some  of  the  vertebrae  was  two  and 

a  half  inches  in 
diameter,  indi- 
cating a  reptile 
of  gigantic  di- 
mensions. 

Many  other 
genera  have  been 
described  by  au- 
thors both  in 
Europe  and 
America.  Among 
these,  Baphetes, 
Raniceps,  Hyler- 
peton,  Hylono- 
mus,  and  Am- 

phibamus  from  America,  and  Anthracosaurus,  Ophiderpeton,  and  Apa- 
teon  from  Europe,  are  best  known.  The  Baphetes  and  the  Anthra- 
cosaurus attained  gigantic  size. 


FIG.  582.— Two  Vertebrae  of  Eosanrus  Acadianus  (after  Marsh). 


FIG.  583.— Ptyonius  (after  Cope). 


404: 


PALAEOZOIC  SYSTEM   OF  ROCKS. 


Very  recently  a  large  number  (thirty-four  species  referable  to  seven- 
teen genera)  of  small  Amphibians  have  been  brought  to  light  by  the 
Ohio  Survey,  and  described  by  Cope.  These  are  all,  or  nearly  all,  Laby- 
rinthodonts  (Stegocephali,  Cope).  Some  of  them  have  the  usual  broad 
heads  of  Amphibians,  but  a  large  number  are  remarkable  for  their 
long,  limbless,  snake-like  forms  and  pointed  heads.  These  are  evidently 
among  the  lowest  form  of  Amphibians,  and  have  strong  affinities  also 
with  Ganoid  fishes.  Figs.  583  and  584  represent  two  of  the  Ohio  Am- 
phibians. 

Some  General  Observations  on  the  Earliest  Reptiles. — With  the  pos- 
sible exception  of  the  Eosaurus,  all  the  reptiles  of  the  Carboniferous 
were  Labyrinthodonts.  They  are  so  called  on  account  of  the  extraordi- 
nary labyrinthine  structure  of  their  teeth,  produced  by  the  intricate 
infolding  of  the  surface  and  of  the  cavity.  The  same  structure  is  ob- 
served in  Ganoid  teeth,  but  in  a  far  less  degree.  The  simple  infold- 
ings  of  Ganoids  (Fig.  449,  p. 
342)  become  intricate  in  Laby- 
rinthodonts (Fig.  585). 

The  Labyrinthodonts  were 


FIG.  584.— Tuditanus  radiatus,  x  |  (after  Cope).       FIG.  585.—  Section  of  Tooth  of  a  Labyrinthodont 

probably  the  most  complete  example  of  a  connecting  type  which  has 
yet  been  discovered.  First,  they  were  true  Amphibians  in  the  strictest 
sense,  having  all  of  them  in  the  early  stages  of  their  life — some  through- 
out life — both  lungs  and  gills,  and  thus  connecting  water-breathers 
with  air-breathers.  Again,  they  were  very  different  from  the  slimy- 
skinned  Amphibians  of  the  present  day,  in  being  covered,  at  least 
partly,  with  bony  plates  or  scales  over  the  body,  and  with  closely-fitting 
bony  plates  over  the  head.  Again,  they  differed  wholly  from  the  pres- 
ent Amphibians  in  having  jaws  thoroughly  armed  with  very  large  and 
powerful  teeth,  the  structure  of  which  is  labyrinthine.  All  of  these 
characters  connected  them  with  Sauroid  fishes  wrhich  preceded  them, 
and  the  great  Saurian  reptiles  which  succeeded  them.  Finally,  they 
seemed  to  possess  also  characters  connecting  them  with  several  orders 
of  subsequently-existing  reptiles.  In  the  Labyrinthodonts  and  Sauroid 


SOME  GENERAL  OBSERVATIONS  ON  THE  WHOLE  PALEOZOIC.    405 

fishes  we  can  almost'  find  the  point  of  separation  of  the  two  great 
branches,  Reptile  and  Fish,  of  the  vertebrate  stem;  and  in  the  former 
the  commencing  differentiation  of  the  several  orders  of  Reptiles.  All 
the  earliest  amphibians  had  persistent  notochord  (Cope). 

Some  General  Observations  on  the  Wliole  Palceozoic. 

"We  have  defined  geology  as  the  history  of  the  evolution  of  the 
earth.  Evolution*  therefore,  is  the  central  idea  of  geology.  It  is  this 
idea  alone  which  makes  geology  a  distinct  science.  This  is  the  cohe- 
sive principle  which  unites  and  gives  significance  to  all  the  scattered 
facts  of  geology ;  which  cements  what  would  otherwise  be  a  mere  inco- 
herent pile  of  rubbish  into  a  solid  and  symmetrical  edifice.  It  seems 
appropriate,  therefore,  that  at  the  end  of  the  long  and  eventful  Palaeo- 
zoic era  we  should  glance  backward  and  briefly  recapitulate  the  evi- 
dences of  progressive  change  (evolution),  physical,  chemical,  and  vital. 

Physical  Changes. — The  Palaeozoic  era  opened  on  this  continent 
with  a  V-shaped  mass  of  land — the  Laurentian  area — to  the  north ;  also, 
a  land-mass  of  Laurentian  rocks,  of  unknown  shape  and  extent,  on  the 
eastern  border,  and  probably  some  islands  and  masses  of  larger  extent 
in  the  Basin  and  Rocky  Mountain  regions.  This  condition  of  things  is 
represented  on  the  map  on  page  292.  Throughout  the  Palaeozoic  era 
there  was  an  accretion  of  land  to  this  nucleus  by  upheaval  of  con- 
tiguous sea-bottoms ;  a  development  of  the  continent  southward  (and 
perhaps  northward)  from  the  northern  area,  and  both  eastward  and 
westward  from  the  eastern  border  area,  until  at  the  end  of  the  Palaeo- 
zoic the  eastern  half  of  the  continent  included  certainly  all  the  Lau- 
rentian, Silurian,  Devonian,  and  Carboniferous  areas  shown  on  the  map 
on  page  291,  and  probably  also  some  on  the  eastern  border  of  the  eastern 
Archaean  area,  which  was  subsequently  covered  by  the  sea,  and  is  there- 
fore now  concealed  by  more  recent  deposits.  The  loss  of  Palaeozoic 
land  on  the  eastern  border  probably  took  place  during  the  Appalachian 
revolution.  In  the  Rocky  Mountain  region  the  development  was  prob- 
ably less  steady.  Unconformity  of  Carboniferous  on  Silurian  strata 
shows  extensive  land-areas  there  during  Devonian  times.  Thus  it  is 
seen  that  the  continent  was  already  sketched  in  the  beginning  of  the 
Palaeozoic,  and  the  process  of  development  went  on  during  that  era,  so 
that  at  the  end  the  outlines  of  the  continent  were  already  unmistak- 
able. We  shall  trace  the  further  development  hereafter. 

Chemical  Changes. — Progressive  changes  in  chemical  conditions  are 
no  less  evident.  At  first — i.  e.,  before  the  Archaean  era — before  the  ex- 
istence of  life  on  the  earth — the  atmosphere,  as  shown  by  Hunt  (Essays, 
p.  40  et  seq.),  was  loaded  with  carbonic  acid,  representing  all  the  car- 
bon and  carbonates  in  the  world ;  with  sulphuric  acid  representing  all 
the  sulphur  and  sulphates  ;  with  hydrochloric  acid  representing  all  the 


406 


PALEOZOIC  SYSTEM   OF  ROCKS. 


chlorides  j  and  with  aqueous  vapor  representing  all  the  ivater  on  the 
earth.  Of  course,  such  a  condition  rendered  life  impossible.  From 
this  primeval  atmosphere,  by  cooling,  the  strong  acids  were  first  pre- 
cipitated with  the  water ;  and  afterward  more  slowly  the  carbonic  acid, 
by  the  action  of  this  acid  upon  the  primeval  silicates,  with  the  forma- 
tion of  carbonates,  especially  limestone.  All  limestones,  therefore,  rep- 
resent so  much  carbonic  acid  withdrawn  from  the  air.  This  with- 
drawal proceeded  through  the  whole  Archaean,  Silurian,  and  Devonian. 
During  the  Carboniferous,  the  purification  of  the  air  was  accelerated 
by  the  growth  of  vegetation  and  its  preservation  as  coal,  as  already  ex- 
plained, pages  356  and  382.  In  this  method  of  withdrawal  the  oxygen 
of  the  carbonic  acid  is  returned,  and  the  air  becomes  more  oxygenated. 
Progressive  Change  in  Organisms.  —  Corresponding  with  these 
changes,  physical  and  chemical,  it  is  natural  to  expect  changes  in  spe- 
cies, genera,  families,  etc.,  of  organisms :  and  such  we  find.  The  law 
of  continuance  or  geological  range  of  species,  genera,  families,  orders,  is 


I.  Paradoxides. 


2.  Bathyurus,  Agnos- 1 
tus,  etc ( 


3. '  Asaphns,      Remo- 
pleurides, 
nucleus, 


Remo- ) 
es,     Tri-  V  — 
s,  etc ) 


4.  Calymene,  Acidas- ) 

pis,  etc ) 

5.  Homalonotus,    Li-  | 

chas,  etc ) 


6.  Phillipsia,  Griffith- 
ides. ... 


7.  Distribution  of 
species  of  Caly 
mene,  etc 


FIG.  586.— Diagram  illustrating  Distribution  of  Families,  etc.,  in  Time. 

very  similar  to  that  of  extent  or  geographical  range  of  the  same  groups ; 
i.  e.,  the  laws  of  distribution  in  time  are  similar  to  those  of  distribution 
in  space.  The  period  of  continuance  (range  in  time)  of  species  is,  of 
course,  less  than  that  of  genera  (because  the  genus  is  continued  in  other 
species  of  same  the  genus),  and  that  of  genera  less  than  that  of  fami- 


GENERAL   PICTURE   OF   PALEOZOIC   TIMES.  407 

lies,  etc.  According  to  Prof.  Hall,  there  have  been  in  the  Silurian  and 
Devonian  ages  alone  at  least  thirty  almost  complete  changes  of  species. 
The  changes  of  genera  are,  of  course,  much  less  numerous,  and  those 
of  families  still  less  than  those  of  genera.  These  general  laws  may  be 
illustrated  by  any  Palaeozoic  order ;  but  I  select  the  order  of  Trilobites, 
because  they  are  very  numerous,  very  diversified,  and  well  studied,  and 
because  they  came  in  with  the  Palaeozoic,  continued  throughout  the 
whole  era,  and  then  passed  away  forever. 

The  diagram  (Fig.  586)  illustrates  these  laws  in  the  order  of  Trilo- 
bites. It  is  seen  that  this  order  continues  through  the  whole  era, 
commencing  in  small  numbers,  reaching  its  highest  development  in 
the  Lower  Silurian,  and  declining  to  the  end.  But  the  families  are 
changed  several  times.  Six  groups  are  given,  to  show  how  they  come 
and  go  successively.  If  we  should  attempt  the  distribution  of  genera, 
the  changes  would  be  much  more  numerous,  and  of  species  still  more  so. 
In  the  lower  portion  of  the  diagram  we  have  attempted  to  show  in  a 
very  general  way  how  the  distribution  of  species  of  Calymene  and 
Acidaspis  might  be  represented. 

General  Comparison  of  the  Fauna  of  Palaeozoic  with  that  of  Neozoic 
Times. — The  changes  above  explained  were  gradual ;  but  at  the  end  of 
the  Palaeozoic  there  occurred  a  more  rapid  and  revolutionary  change, 
and  the  greatest  which  has  ever  occurred  in  the  history  of  the  organic 
kingdom.  As  human  history  is  primarily  divided  into  Ancient  and 
Modern,  so  the  whole  history  of  the  earth  may  be  properly  divided  into 
Paleozoic  and  Neozoic  times.  We  wish  to  contrast  broadly  the  faunae 
of  these  two  great  divisions  of  time.  In  the  diagram  on  next  page, 
the  vertical  line  represents  the  dividing  line  between  the  old  and  the 
new  time-world.  In  this  country  it  is  appropriately  called  the  Appa- 
lachian revolution.  On  the  left  is  the  Palaeozoic,  on  the  right  the 
Neozoic.  When  families  or  orders  of  animals  are  placed  on  one  or  the 
other  side  without  mark,  it  means  that  they  are  the  only  kind  of  the 
contrasted  families  found  on  that  side,  or  nearly  so.  If  the  orders  or 
families  so  placed  are  marked  with  the  sign  -|-,  it  means  that  they  are 
the  predominant  kinds.  For  example,  among  Cephalopods,  the  Tetra- 
branchs,  or  shelled  family,  are  the  only  kinds  found  in  the  Palaeozoic ; 
in  the  Neozoic,  both  families  exist,  but  the  Dibranchs  or  naked  ones 
vastly  predominate. 

General  Picture  of  Paleozoic  Times. 

Perhaps  it  is  not  inappropriate  to  group  some  of  the  more  impor- 
tant facts  in  a  very  brief  outline-picture  of  Palaeozoic  times.  We  must 
imagine,  then,  wide  seas  and  low  continents  of  small  extent ;  a  hot, 
moist,  still  air,  loaded  with  carbonic  acid,  stifling  and  unsuited  for  the 
life  of  warm-blooded  animals.  If  an  observer  had  walked  along  those 


408  PALAEOZOIC  SYSTEM  OF  ROCKS. 


Palaeozoic  times. 


.Neozoic  times. 


I 
RADIATA. 

Corah. 

Quadripartita |  . .  Sexpartita. 

EcMnoderms, 

4-   4-  Stemmed,  or  Crinoids [  .  .Free,  or  Echinoids  and  Asteroids  4-  4- 

Crinoids. 
4-  Armless,  or  simple  arms j  .  .Plumose  arms. 


MOLLUSKS. 

Bivalves. 

4-  Brachiopods |  . .  Lamellibranchs  4-   4- , 

Brachiopods. 

4-  Square-shouldered |  .  .Sloping-shouldered. 

Lamellibranchs. 

4-  Unsiphonated |  .  .Siphonated  4- . 

Gasteropoda, 

Marine |  .  .Land,  fresh-water,  and  marine. 

Marine. 

Unbeaked — Herbivorous |  . .  Beaked — Carnivorous  4- , 

Ccphalopods, 

Shelled,  or  Tetrabranchs f  .  .Naked,  or  Dibranchs  4-  4-, 

Shelled. 

+  Straight I  ..Coiled, 

Orthoceratites. 

N a u t i 1 o i d s. 

Goniatites, 

Ceratites. 

Ammonites. 


ARTICULATA. 


Crustacea. 


Palaeocarida 


.Neocarida  4-. 


Trilobites. 

Eurypterids, 

Limuloids. 

I          Macrourans, 

Brachyourans. 


VERTEBRATA. 

FisJies. 

Heterocercals I  .  .Homocercals  4- . 

Ganoids  and  Placoids f Tcleosts  + . 

Placoids. 
Cestracionts. 

Hybodonts 

Squalodonts. 
Reptiles. 
Amphibians j  .  .True  Reptiles, 


early  beaches  he  would  have  found  cast  up,  in  great  numbers,  the  shells 
of  Brachiopods ;  clinging  to  the  rocks  and  hiding  away  among  their 


TRANSITION  FROM   THE  PALEOZOIC   TO   THE   MESOZOIC.          409 

hollows,  instead  of  sea-urchins  and  star-fishes  and  crabs,  he  would  have 
found  crinoids  and  trilobites.  In  the  open  sea  he  would  have  found  as 
rulers,  instead  of  whales  and  sharks  and  teleosts  and  cuttle-fish,  huge 
cuirassed  Sauroids  and  the  straight-chambered  Orthoceras.  Turning 
to  the  land,  he  would  have  seen  at  first  only  desolation ;  for  there  were 
almost  no  land-plants  until  the  Devonian,  and  almost  no  land-animals 
until  the  Coal.  During  the  Coal  there  were  extensive  marshes,  over- 
grown with  great  trees  of  Sigillaria,  Lepidodendron,  and  Calamites, 
with  dense  underbrush  of  Ferns,  inhabited  by  insects  and  amphibians ; 
no  umbrageous  trees,  no  fragrant  flowers  or  luscious  fruits,  no  birds,  no 
mammals.  These  "  dim,  watery  woodlands  "  are  flowerless,  fruitless, 
songless,  voiceless,  except  the  occasional  chirp  of  the  grasshopper.  If 
the  observer  were  a  naturalist,  he  would  notice,  also,  the  complete  absence 
of  modern  types  of  plants  and  animals — it  would  be  like  another  world. 
This  long  dynasty  was  overthrown,  this  reign  of  Fishes  and  Amphib- 
ians ended,  the  physical  conditions  described  above  were  changed,  and 
the  whole  fauna  and  flora  destroyed  or  transmuted  by  the  Appalachian 
revolution.  At  the  end  of  the  Palaeozoic,  the  sediments  which  had  been 
so  long  accumulating  in  the  Appalachian  region  at  last  yielded  to  the 
slowly-increasing  horizontal  pressure,  and  were  mashed  and  folded  and 
thickened  up  into  the  Appalachian  chain,  and  the  rocks  metamorphosed. 
In  America,  this  chain  is  the  monument  of  the  greatest  revolution 
which  has  taken  place  in  the  earth's  history.  At  the  same  time  great 
changes  took  place  in  the  West  also.  The  Utah  basin  region  was  up- 
heaved to  form  land,  the  Nevada  basin  region  sank  and  became  sea- 
bottom,  and  the  Pacific  shore-line  was  transferred  eastward  to  the  117th 
meridian  about  Battle  Mountain.  In  other  words,  the  Basin  region 
Palaeozoic  continent  was  transferred  eastward  its  own  breadth  to  form 
the  Basin  region  Mesozoic  continent  (King).  Similar  and  very  exten- 
sive changes  in  physical  geography  must  have  taken  place  in  other  por- 
tions of  the  globe,  otherwise  we  can  not  account  for  the  enormous 
changes  in  physical  conditions  and  fauna  and  flora.  Many  of  these  have 
been  traced,  but  we  can  not  yet  trace  them  as  clearly  as  in  America. 

Transition  from  the  Palceozoic  to  the  Mesozoic — Permian  Period. 

The  Permian  a  Transition  Period. — The  Palseozoic  era  was  closed 
and  the  Mesozoic  inaugurated  by  the  Appalachian  revolution.  All  the 
great  revolutions  in  the  earth's  history  are  periods  of  oscillations.  Such 
oscillations  produce  unconformity.  They  also  produce  changes  of  cli- 
mate, and  therefore  of  fauna  and  flora.  We  find,  therefore,  that  the 
Mesozoic  rocks  are  universally,  or  nearly  universally,*  unconformable 

*  In  the  Rocky  Mountain  region  there  seems  to  be  complete  conformity  in  some 
places.  (King,  Fortieth  Parallel  Survey,  vol.  i,  p.  266.) 


410  PALAEOZOIC  SYSTEM  OF  ROCKS. 

on  the  Carboniferous ;  and,  corresponding  with  this  unconformity, 
there  is  a  wonderful  change  in  fauna  and  flora — a  change  the  greatness 
of  which  we  have  attempted  to  show  in  the  contrast  on  the  preceding 
page.  Now,  the  older  geologists  regarded  this  change  as  one  of  instan- 
taneous destruction  and  recreation,  because  they  took  no  account  of  a 
lost  interval.  But  we  have  already  shown  (pp.  181,  295)  that  in  all 
cases  of  unconformity  there  is  such  a  lost  interval,  which  in  some  cases 
is  very  large.  In  order  to  account  for  the  very  great  change  in  the 
organic  world,  it  is  only  necessary  to  suppose  that  periods  represented 
by  general  unconformity  are  critical  periods  in  the  earth's  history — 
periods  of  rapid  change  in  physical  geography,  climate,  and  therefore 
of  rapid  change  in  fauna  and  flora,  by  the  passing  out  of  old  types  and 
the  differentiation  of  new  types.  Unfortunately,  in  the  earth's  history 
as  in  human  history,  it  is  exactly  these  critical  periods — these  periods  of 
change  and  revolution — the  record  of  which  is  apt  to  be  lost.  In  both 
histories,  too,  this  is  truer  the  farther  back  we  go.  Of  the  long  inter- 
val between  the  Archaean  and  Palaeozoic,  not  a  leaf  of  record  has  yet 
been  recovered  with  any  certainty ;  but  of  the  interval  now  under  dis- 
cussion many  leaves  of  record  have  been  recovered.  These  have  been 
bound  together  in  a  separate  volume  or  chapter  and  called  the  Permian. 
I  shall  regard  the  Permian,  therefore,  as  essentially  a  transition  period  ; 
its  rocks  were  deposited  during  the  period  of  commotion ;  its  fossil 
types  are  in  a  state  of  change,  though  more  nearly  allied  to  the  Palae- 
ozoic. 

From  what  has  just  been  said,  it  will  be  anticipated  that  the  uncon- 
formity of  the  Mesozoic  on  the  Palaeozoic  sometimes  takes  place  be- 
tween the  lowest  Mesozoic  and  the  Permian,  and  sometimes  between 
the  Permian  and  the  Coal.  The  Permian,  therefore,  is  sometimes  con- 
formable with  the  Coal,  as,  e.  g.,  in  this  country,  sometimes  conform- 
able with  the  Triassic,  as  in  England.  It  thus  allies  itself  stratigraphi- 
cally  sometimes  with  the  Palaeozoic,  sometimes  with  the  Mesozoic. 
Paleontologically  it  is  always  more  allied  to  the  Palaeozoic.  The  Eng- 
lish section,  and  the  history  of  opinion  concerning  it,  admirably  illus- 
trate this  point.  Fig.  587  is  an  ideal  section  through  the  Devonian, 

the  Coal  and  Tri- 
assic (Lower  Meso- 
zoic) of  England. 
Lying  unconforma- 
bly  on  the  eroded 

Fie.587.-(AfterLyell.)  J 

surface  ot  the  Coal, 

5,  there  is  seen  a  continuous  and  perfectly  conformable  series  of  strata, 
a.  This  series,  moreover,  is  lithologically  characterized  throughout, 
especially  the  lower  part,  by  frequent  alternations  of  Red  sandstones, 
and  therefore  has  been  called  New  Red  sandstone,  to  distinguish  it  from 


TRANSITION  FKOM   THE   PALAEOZOIC   TO   TUB   MESOZOIC. 

the  Devonian,  which  is  often  called  Old  Red  sandstone.  It  is  further 
distinguished  throughout,  especially  the  upper  part,  by  variegated  shales, 
and  therefore  called  altogether  Poikilitic  group.  It  is  also  distin- 
guished throughout  by  the  presence  of  salt,  and  therefore  called  the 
Saliferous  group.  Here,  then,  there  were  the  strongest  reasons  for  re- 
garding the  whole  as  one  group,  distinctly  separated  by  unconformity 
from  the  underlying  Coal.  The  upper  part  of  this  continuous  series 
contained  undoubted  Mesozoic  fossils.  The  line  of  unconformity  was, 
therefore,  naturally  believed  to  be  the  line  between  Palaeozoic  and  Meso- 
zoic. Unfortunately,  the  lower  portion  is  very  barren  of  fossils,  and 
this  means  of  correcting  the  stratigraphic  conclusion  was  at  first  nearly 
wanting.  When  fossils  were  discovered  in  sufficient  numbers,  how- 
ever, they  showed  a  greater  alliance  with  the  unconformable  Coal  below 
than  with  the  conformable  strata  above.  Thus,  if  we  make  the  division 
between  Palaeozoic  and  Mesozoic  on  stratigraphical  grounds,  we  would 
find  it  between  the  Coal  and  the  overlying  strata ;  while,  if  we  make  it 
on  paleontological  grounds,  we  would  have  to  draw  the  line  through 
the  midst  of  the  conformable  strata,  «,  giving  one  half  to  the  Palaeozoic 
and  the  other  half  to  the  Mesozoic.  The  lower  Palaeozoic  half  is  called 
the  Permian* 

As  a  broad  general  fact,  therefore,  the  great  commotion  which  is 
called  the  Appalachian  revolution  took  place,  or  commenced  to  take 
place,  at  the  end  of  the  Coal  period.    But  the  fauna  and  flora  were  not 
immediately       extermi- 
nated, but  struggled  on, 
maintaining,  as  it  were, 
a  painful  existence  un- 
der changed  conditions, 
themselves      meanwhile 
changing,  until  complete 
and  permanent  harmony 
was  re-established  with 
the  opening  of  the  Mes- 
ozoic.    If  we  may  use  an  FIG-  588.  FIG.  591. 

il  In  strati  on    flip    Armflln      FIGS.  588-592.— AMERICAN  PERMIAN  FOSSILS  (after  Meek):  588. 

3U,  II  6  Appaia-  Enmicrotis  Hawni.    589.   Myalina  Permiana.     590.  Bake- 

Chian  revolution  Was  the  wellia  parva.    591.  Pleurophorus  subcuneatus.    592.  A  Gas- 

death-sentence  of  Palae- 
ozoic types,  but  the  sentence  was  not  instantly  executed.     This  transi- 
tion period,  between  the  sentence  and  the  execution  of  Palaeozoic  types, 
is  the  Permian. 

It  is  well  here  to  draw  attention  to  the  fact  of  this  great  change  of 

*  In  Germany  it  is  closely  allied  stratigraphically  with  the  Triassic,  and  therefore  by 
many  put  in  the  Mesozoic,  and  called  Dyass. 


412 


PALEOZOIC   SYSTEM   OF  ROCKS. 


FIG.  596. 


FIG.  697. 

FIGS.  593-597.— EUROPEAN  PERMIAN  FOSSIL?  :  Plants— 593.  Walchia  piniformis  (Permian  of  Europe). 
594.  Ginkophyllura.  Fishes— 595.  Platysomas  gibbosus  (Permian  of  Europe).  596.  Restoration 
of  Palaeoniscus.  Reptile— 597.  Limnerpeton  laticeps,  natural  size  (after  Fritsch). 

organisms,  the  greatest  in  the  whole  history  of  the  earth,  taking  place 
in  the  midst  of  conformable  strata  (Fig.  587,  a).  Evidently  the  change 
must  have  been  comparatively  rapid. 


TRANSITION  FROM   THE   PALEOZOIC  NO   THE   MESOZOIC.          413 

We  have  given  the  history  of  change  of  opinion  in  regard  to  the 
English  section  (Fig.  587),  because  it  is  a  type  of  many  discussions  and 
changes  which  have  occurred  and  will  still  occur  in  geological  opinion. 

Area  in  the  United  States. — The  Permian  has  been  found  in  the 
United  States,  in  Kansas,  bordering  on,  and  conformable  with,  the  coal 
of  that  region  (map,  p.  287) ;  also  in  New  Mexico  and  Western  Texas, 
and  probably  also  overlying  the  coal  of  Illinois  (Cope).  It  gradates  so 
completely  into  the  upper  Coal-measures  that  no  attempt  has  been 
made  to  separate  them  in  the  map.  Until  recently  nothing  of  interest 
has  been  found  in  the  American  Permian,  except  a  few  shells  (Figs. 
588-592),  but  now  a  considerable  number  of  fishes,  amphibians,  and 
reptiles  are  known. 

An  elementary  treatise  like  this  must  dwell  mainly  on  culminating 
periods,  and  their  characteristic  forms ;  and  yet  to  the  philosophic  stu- 
dent it  is  the  transitional,  forms  and  periods  which  are  the  most  inter- 
esting. The  Permian  is  pre-eminently  such  a  transitional  period,  and 
contains  many  transitional  forms.  In  it  we  have  a  passing  away  of 
Palaeozoic  types,  a  coming  in  of  Mesozoic  types,  and  a  coexistence  of 
the  two  side  by  side.  The  change  from  the  one  to  the  other,  there- 
fore, was  not  sudden  and  by  exterminations  and  recreations,  but  gradu- 
ally by  extinction  of  some  old  forms  and  modification  of  others  into 
new  forms ;  and  all  the  new  forms  were  thus  derived. 

The  main  features  of  the  Permian  life,  therefore,  were :  1.  A  lin- 
gering of  coal  types  of  plants,  such  as  the  Lepidodendrids  and  Cala- 
mites,  and  many  genera  of  Ferns,  but  extinction  of  Sigillarids  and 
increase  and  advance  of  Conifers  to  more  varied  and  modern  forms, 
such  as  Walchia,  Ginkophyllum,  etc.  (Figs.  593,  594).  2.  A  lingering 
of  Orthoceratites,  square-shouldered  Brachiopods,  such  as  Productus 
and  Spirifer,  and  perhaps  of  Goniatites,  but  complete  extinction  of 
Trilobites  and  Eurypterids.  3.  A  continuance  of  Ganoids,  but  under 
more  modern  forms  (Figs.  595,  596).  4.  Amphibians  continue  in  the 
form  of  Labyrinthodonts  (Stegocephali  of  Cope),  of  which  some  are 
very  modern  in  form  (Fig.  597),  but  true  reptiles  are  introduced  in  con- 
siderable numbers.  These  first  reptiles,  as  might  have  been  expected, 
are  wonderfully  generalized  in  structure.  They  connect,  on  the  one 
hand,  with  Amphibians,  from  which  they  were  derived,  and,  on  the  other, 
with  the  lowest  Mammals,  to  which  they  gave  origin.  On  account  of 
this  connection  with  Mammals,  Cope  has  called  them  Theromorphs 
(beast-like).  Thus,  then,  we  have,  at  this  time,  Stegocephali,  connect- 
ing Ganoid  fish  with  reptiles,  and  Theromorphs,  connecting  Amphib- 
ians with  Mammals.  This  is  shown  in  the  following  schedule : 


414  MESOZOIC  ERA— AGE   OF  REPTILES. 

CHAPTER  IV. 

MESOZOIC  ERA— AGE  OF  REPTILES. 

THE  Palseozoic  era,  we  have  seen,  was  very  long,  and  very  diversi- 
fied in  dominant  types,  of  both  animals  and  plants.  It  was  during  this 
long  era  that  originated  nearly  all  the  great  branches,  and  even  sub- 
branches,  of  the  organic  kingdom.  We  have  during  this  era,  therefore, 
three  very  distinct  ages :  an  age  of  Invertebrates,  an  age  of  Fishes,  and 
an  age  of  Acrogens  and  Amphibians.  The  Mesozoic  was  far  less  long 
and  far  less  diversified  in  dominant  types.  It  consists  of  only  one  age, 
viz.,  the  age  of  Eeptiles.  Never  in  the  history  of  the  earth,  before  or 
since,  did  this  class  reach  so  high  a  point  in  numbers,  variety  of  form, 
size,  or  elevation  in  the  scale  of  organization. 

General  Characteristics. — The  general  characteristics  of  the  Meso- 
zoic era  are  the  culmination  of  the  class  of  Reptiles  among  animals,  and 
of  Cycads  among  plants,  and  the  first  appearance  of  Teleosts  (common 
osseous  fishes),  Birds,  Mammals  among  animals,  and  of  Palms  and 
Dicotyls  among  trees. 

Subdivisions. — The  Mesozoic  era  is  divided  into  three  periods,  viz. : 
1.  Triassic,  because  of  its  threefold  development  where  first  studied  in 
Germany ;  2.  Jurassic,  because  of  the  splendid  development  of  its 
strata  in  the  Jura  Mountains ;  3.  Cretaceous,  because  the  chalk  of  Eng- 
land and  France  belongs  to  this  period. 

13.  Cretaceous  period. 
2.  Jurassic  period. 
1.  Triassic  period. 

In  this  country  the  Triassic  and  Jurassic  are  not  so  distinctly  sepa- 
rable as  they  are  in  Europe,  nor  as  they  are  from  the  Cretaceous.  They 
form,  in  fact,  one  series,  and  if  the  Mesozoic  had  been  studied  first  in 
this  country,  the  whole  would  probably  have  been  divided  into  only  two 
periods.  We  shall  therefore  speak  of  the  Mesozoic  of  this  country  as 
consisting  of  two  periods,  viz.,  the  Jura- Trias  and  the  Cretaceous.  On 
account  of  their  fuller  development  in  Europe,  it  will  be  best  to  speak, 
first,  of  the  Triassic  generally,  then  of  the  Jurassic  generally,  taking 
our  illustrations  mainly  from  European  sources,  and  then  of  the  Jura- 
Trias  in  America.  Also,  on  account  of  the  comparative  poverty  of  the 
Trias  in  remains,  we  will  dwell  much  less  on  this  period  than  on  the 
subsequent  Jurassic ;  for  in  this  latter  period  culminated  all  the  dis- 
tinctive characters  of  the  Reptilian  age. 


TRIASSIC  PERIOD. 


415 


SECTION  1. — TRIASSIC  PERIOD. 

As  already  stated,  the  Triassic  strata  are  always  unconformable 
with  the  Coal,  and  the  period  opens  with  a  fauna  and  flora  wholly  and 
strikingly  different  from  the  preceding.  In  some  places,  however, 
there  is  found  an  intermediate  series,  the  Permian,  sometimes  con- 
formable with  the  Coal  and  unconformable  with  the  Trias,  sometimes 
conformable  with  the  Trias  and  unconformable  with  the  Coal.  Its  fauna 
and  flora  are  also  to  some  extent  intermediate,  though  more  nearly  al- 
lied to  those  of  the  Coal.  The  explanation  of  this  has  already  been  given. 

Subdivisions. — The  subdivisions  of  the  Triassic  rocks  and  period  in 
several  countries  are  given  below  : 


GERMAN. 

FRENCH. 

ENGLISH. 

3.  Keuper. 

Marne  irise'e. 

Variegated  marl. 

2.  Muschelkalk. 

Muschelkalk. 

Wanting. 

1.  Bunter  Sandstein. 

Gres  bigarre. 

Upper  New  Red  sandstone. 

FIGS.  59& 


FIG.  600. 


FIGS.  598-600.— TRIASSIC  CONIFERS  AND  CYCADS  (after  Nicholson):   598.  Voltzia  heterophylla,  a 
conifer.    599.  Pterophyllum  Jsegeri,  a  cycad.    600.  Podozamites  Emmonsi,  a  cycad. 


416  .      MESOZOIC  ERA— AGE   OF  REPTILES. 

The  flora  of  the  Trias  is  very  imperfectly  known.  We  find,  how- 
ever, no  longer  the  great  coal-making  trees  of  the  Carboniferous — Sig- 
illarids,  Lepidodendrids,  and  Calamites  —  though 
Tree-ferns  still  continue  in  abundance,  but  of  differ- 
ent types  from  those  of  the  coal.  The  forest-trees 
seem  to  have  been  principally  Tree-ferns,  Cycads, 
and  Conifers,  although  the  last  two  did  not  reach 
their  highest  development  until  the  next  period. 
For  this  reason  we  will  put  off  the  fuller  discussion 
of  them  until  we  come  to  that  period. 

Animals. — Among  Echinoderms  we  find  no  longer 
any  Cystids  and  Blastoids;  but  Crinids,  beautiful 
lily  Encrinites,  with  long  plumose  arms,  are  very 
abundant  (Fig.  601). 

Among  jBrachiopods  the  familiar  square-shoul- 


FIG.  601.— Encrinus  liliformis.  FIG.  602.— Aspidura  loricata,  au  asteroid. 

dered  forms,  including  the  Spirifer  family,  the  Strophomena  family,  and 
the  Productus  family,  are  almost  if  not  wholly  gone ;  only  a  few  Spiri- 
fers  remain.'  Among  Ceplialopods,  we  find  no  longer  Orthoceratites 
or  Goniatites,  but  Ceratites  (Fig.  609)  take  their  place,  and  Ammo- 
nites begin.  In  Ceratites,  the  suture  is  more  complex  than  in  Gonia- 
tites,  but  not  so  complex  as  the  subsequent  Ammonites.  Among  Crus- 
taceans, we  find  no  longer  Trilobites  nor  huge  Eurypterids,  but  Mac- 
rourans,  which  began  in  the  Carboniferous,  are  now  more  abundant, 
and  of  more  modern  forms  (Fig.  610). 

Insects. — As  already  seen,  all  the  hexapod  insects  of  Palaeozoic  be- 
long to  one  family — the  Palseodictyoptera — but  this  was  a  generalized 
type  connecting  the  three  lower  existing  orders,  viz.,  Orthopters,  Neu- 
ropters,  and  Hemipters.  Now,  with  the  opening  of  the  Trias,  we  have 
these  three  orders  distinctly  differentiated,  and  Coleopters  (beetles) 
added  (Fig.  611).  But  still  the  sucking  insects  are  wanting. 

Fishes. — Among  fishes,  still  we  find  no  Teleosts,  only  Ganoids  and 
Placoids ;  but  while  the  Ganoids  are  some  of  them  heterocercal  or  ver- 
tebrated-tailed  like  the  Palaeozoic  Ganoids,  some  are  only  slightly  ver- 
tebrated,  and  some  wholly  non-vertebrated- tailed,  or  homoceral.  The 
Ceratodus,  a  remarkable  genus  of  fishes,  one  species  of  which  still  lives 


TRIASSIC  PERIOD. 


417 


in  Australian  rivers  (Fig.  438,  p.  338),  is  traced  back  to  this  period. 
Being  known  in  a  fossil  state  only  by  the  curious  palatal  teeth  (Fig. 


PIG.  60ft 


Fro.  607. 


FIG.  608. 


FIGS.  603-608.— LAMELLIBKANCHS  (after  Nicholson):  603.  Daonella  Lommelli.  604.  Pecten  Valoni- 
ensis.  605.  Myophoria  lineata.  606.  Cardium  Rhseticum.  607.  Avicula  contorta.  608.  Avicula 
socialis. 

612),  it  has  heretofore  been  classed  with  Placoids.     The  Placoids  are 
partly  Cestracionts  (Fig.  613),  and  partly  Hybodonts  (Fig.  614). 


FIG.  609.— Ceratites  nodosus. 


FIG.  611.— Glaphroptera  pterophylli  (after  Heer). 


Reptiles. — The  reptiles  of  the  Triassic  are  imperfectly  known.    They 
belong  mainly  to  four  orders,  viz. :  1.  Labyrinthodonts  ;  2.  RJiyncosaurs 
(beaked  Saurians) ;  3.  Anomodonts  (lawless-toothed) ;   and,  4.  Tlierio- 
donts  (beast-toothed).     The  last  two  are  sometimes  united  in  one  order 
-Theromorpha.     The  Labyrinthodonts  are  found  also  in  the  Carbon- 
iferous and  Permian ;  but  the  other  three  orders  are  characteristic  of 
the  Triassic  and  Permian,  and  therefore  of  peculiar  interest. 
27 


418 


MESOZOIC  ERA— AGE   OF  REPTILES. 


Labyrintliodonts  have  already  been  described,  in  connection  with 
the  Carboniferous  when  they  first  occur.     They  culminate,  however,  in 

size  and  in  com- 
plexity of  tooth- 
structure — if  not 
in  number  and 
variety  —  in  the 
Triassic,  and  then 
become  extinct. 
In  some  cases  they 
reached  gigantic 
proportions.  The 
head  of  the  Mas- 
todonsaurus  (Fig. 
615)  was  three 
feet  long  and  two 
feet  wide.  The 
tooth  of  the  typi- 
cal genus  Labyrinthodont  was  three  and  a  half  inches  long  and  one  and 
a  half  in  diameter  at  the  base  (Fig.  617).  The  complex  labyrinthine 
structure  is  shown  in  Fig.  618.  Attention  was  first  drawn  to  these 


FIG.  613. 


FIG.  614. 


FIGS.  61S-614.— TRIASSIC  FISHES  :  612.  <z,  Dental  Plate  of  Ceratodns  ser- 
ratus;  6,  Dental  Plate  of  Ceratodus  altus,  Keuper  (after  Agassiz). 
613.  Acrodus  minimus.  614.  Hybodus  apicalis  (after  Agassiz). 


FIG.  616. 

FIGS.  615,  616.— TRIASSIC  'REfru^n—Labyrintkodonts:  615.  Mastodonsaurns  Jsegeri.    616.  Trema- 

tosaurus  (after  Huxley). 


TRIASSIC  PERIOD. 


419 


animals  by  the  discovery  in  Triassic  strata  of  certain  tracks  made  by 
a  clumsy-footed  animal  (Fig.  619),  which  was  at  first  mistaken  for  a 
mammal  and  called  Cheirotherium  (hand-beast).  Its  true  nature  was 
made  known  by  Prof.  Owen,  who  called  it  Labyrinthodont. 

The  Anomodonts  (lawless- toothed) 
had  jaws  covered  with  horn,  like  tor- 
toises and  birds,  sometimes  toothless, 
as  in  Oudenodon  (Fig.  621),  and  some- 
times with  two  great  canines  only,  as 
in  Dicynodon  (Fig.  620).  These  rep- 
tiles were  of  great  size.  The  head  of 
the  Dicynodon  tigriceps  was  twenty 
inches  long  and  eighteen  inches  wide. 
The  Jthyncosaurs'h'ad  strongly-hooked, 
horny  beaks,  like  that  of  a  parrot  (Fig. 
623  a).  The  curious  reptile  Spheno- 
don,  or  Hatteria,  of  New  Zealand  (Fig. 
623  #),  is  the  nearest  living  ally. 


FIG.  617. 


PIG.  618. 


FIGS.  617,  618.— TRIASSIC  REPTILES— Labyrlnthodonts :  617.  Tooth  of  Labyrinthodon,  natural  size. 
618.  Section  of  same  enlarged,  showing  structure. 

The  Theriodonts  (beast-toothed)  are  so  called  on  account  of  the 
resemblance  of  their  teeth  to  those  of  the  lowest  and  earliest  mammals. 
The  following  are  the  main  points  of  resemblance :  1.  The  teeth  are 
in  three  sets,  viz.,  incisors,  canines,  and  molars.  2.  The  canines  are 
much  larger  than  the  others,  and  separated  from  them  by  a  wide  space 
(diastema).  3.  The  molars  (jaw-teeth)  are  in  many  cases  not  conical, 
like  reptilian  teeth,  but  have  commenced  to  develop  cusps  (Fig.  624) 
like  those  of  mammals,  especially  the  earliest  Mesozoic  mammals. 
(Compare  this  figure  with  Fig.  711,  p.  449.)  The  canines  of  some  of 
these  Theriodonts  have  been  found  five  and  six  inches  long.  A  large 


420  MESOZOIC  ERA— AGE   OF  REPTILES. 


FIG.  624. 

PIGS.  619-624.— TRIASSIC  REPTILES  (after  Owen).  619.  Tracts  of  a  Cheirotherinm-a  Labyrinthodont 
620.  Dicynodon  lacerticeps.  621.  Oudenodon  Bainii.  622.  a  b,  Lycosaurus.  b23.  Rhyncosaure 
—a  Hyperodapedon,  Trias;  6,  sphenodon,  living  (after  Huxley).  624.  Galesaurus  planiceps, 
a,  head;  b,  molar  tooth  magnified  (after  Owen). 


ORIGIN  OF  ROCK-SALT.  4-21 

number  of  these  animals — as  also  of  the  previous  order — have  been 
found  in  the  Karoo  beds  of  South  Africa,  and  described  by  Prof.  Owen. 

Birds. — No  birds  have  yet  been  found  in  the  strata  of  the  Triassic 
age,  unless  we  except  the  so-called  bird-tracks  of  the  sandstone  of 
the  Connecticut  Valley  and  elsewhere,  which  we  will  discuss  further 
on. 

Mammals. — Eemains  of  two  or  three  small  insectivorous  Marsupials 
have  been  found  in  the  uppermost  Triassic,  both  of  Europe  and  of  the 
United  States.  Figures  of  a  tooth  of  one  of  these,  Microlestes  anti- 
quus,  are  given  (Fig  625).  The  remains  of  the  mammals  of  the 
Triassic  are  so  few  and  fragment- 
ary that  it  is  difficult  to  make  out 
their  affinities,  but  it  is  probable 
that  they  were  a  generalized  type 
connecting  marsupials  with  the 
still  lower  monotremes  and  both  *,«.  o^.-Tooth  of  the  i 
with  Theriodont  Reptiles.  But  as  these  are  found  in  very  small  num- 
ber sand  only  in  the  uppermost  Triassic  beds,  and  as  similar  animals  are 
found  in  much  greater  numbers  in  the  Jurassic,  it  seems  best  to  regard 
these  as  anticipations,  and  to  put  off  the  further  discussion  of  the  affini- 
ties of  the  earliest  mammals  until  we  take  up  that  period. 

Mammals  probably  preceded  Birds.  This  is  not  a  little  remarkable. 
But  it  must  be  remembered  that  Birds  are  very  closely  allied  to  Rep- 
tiles, and  may  be  regarded  as  a  secondary  offshoot  of  the  reptilian 
branch. 

Origin  of  Rock-Salt. 

Neither  rock-salt  nor  coal  is  confined  to  the  rocks  of  any  particular 
age.  Both  have  been  formed  in  every  age ;  both  are  forming  now. 
But  as  the  subject  of  the  origin  of  coal-deposits  was  discussed  in  con- 
nection with  that  age  during  which  it  was  accumulated  in  the  greatest 
abundance — the  Carboniferous — so  the  origin  of  rock-salt  is  best  dis- 
cussed in  connection  with  the  so-called  Saliferous  or  Triassic. 

Age  of  Rock-Salt. — As  already  stated,  rock-salt  is  found  in  strata 
of  all  ages,  and  is  forming  now.  Moreover,  there  is  no  period  which 
deserves  the  name  Saliferous  to  the  same  extent  that  the  Carboniferous 
deserves  its  name.  The  salt  of  Syracuse,  New  York,  is  found  in  the 
Upper  Silurian;  that  of  Canada,  which  exists  in  immense  beds  100 
feet  thick,  is  found  in  the  Upper  Silurian  or  Lower  Devonian  ;  that  of 
Pennsylvania  is  Upper  Devonian ;  of  Southwest  Virginia  is  sub-Car- 
boniferous ;  that  recently  discovered  in  Kansas  is  in  the  Trias ;  *  that 
of  Petite  Anse,  Louisiana,  is  uppermost  Cretaceous  or  lowest  Tertiary 
(Hilgard).  In  Europe,  the  English  salt-beds  are  Triassic,  the  German 

*  Hay,  American  Geologist,  vol.  v,  p.  65,  1890. 


422  MESOZOIC   ERA— AGE   OF  REPTILES. 

beds  Triassic  and  Jurassic ;  the  celebrated  Polish  beds  at  Cracow  are 
Tertiary. 

Mode  of  Occurrence. — Salt  occurs  in  immense  beds  of  pure  rock-salt, 
or  else  impregnating  strata.  It  is  obtained  by  direct  mining,  or  else  by 
boiling  down  the  saline  waters  either  of  natural  springs  or  of  artesian 
wells  sunk  into  the  salt-bearing  strata.  The  further  explanation  of  its 
mode  of  occurrence  is  best  and  most  concisely  given  by  comparing  it 
with  coal. 

1.  Like  coal,  it  occurs  in  isolated  basins,  but  these  are  far  more 
limited  than  the  great  coal-fields.  2.  Like  coal,  it  is  interstratified 
with  sands  and  clays,  the  whole  series  repeated  often  many  times.  In 
Galicia,  for  example,  there  are  found  seven  salt-beds  in  the  same  sec- 
tion. In  the  Kansas  Trias  there  are  seven  beds.  Like  coal,  also,  each 
bed  is  usually  underlaid  with  clay.  3.  But  it  differs  from  coal  in  the 
great  thickness  of  the  beds.  In  Canada  the  salt-bed  is  100  feet  thick 
(Gibson).*  In  Cheshire,  England,  there  are  two  beds,  one  100  feet,  the 
other  90  feet  thick,  separated  by  30  feet  of  shale.  At  Stassfurt,  a  salt- 
bed  has  been  penetrated  1,000  feet,  and  the  bottom  not  yet  reached,  f 
The  Berlin  salt- well  is  4,172  feet  deep,  and,  except  the  upper  292  feet, 
penetrates  solid  salt.  J  4.  Recollecting  the  somewhat  limited  extent  of 
basins,  it  is  evident  that  salt-beds  thin  out  far  more  rapidly  than  coal. 
The  English  salt-beds  thin  out  fifteen  feet  per  mile.  Coal,  therefore, 
lies  in  extensive  sheets,  salt  in  lenticular  masses.  5.  Coal  has  its  char- 
acteristic valuable  accompaniment  in  iron-beds,  salt  in  beds  of  gypsum. 
Thus,  as  coal-measures  consist  of  repetitions  of  sands,  clays,  occasional 
limestones,  with  valuable  beds  of  coal  and  iron-ore  many  times  repeated, 
so  salt-measures  consist  of  sands,  clays,  and  occasional  limestones,  with 
valuable  beds  of  salt  and  gypsum  many  times  repeated.  Gypsum-beds 
are  often  entirely  separate  from  salt-beds,  but  each  salt-bed  is  apt  to  be 
underlaid  by  gypsum.  6*  While  coal-measures  are  remarkable  for  the 
abundance  of  organic  remains,  both  vegetable  and  animal,  salt-meas- 
ures are  equally  remarkable  for  extreme  poverty  in  this  respect.  The 
presence  of  these  remains  in  the  one  case,  and  their  absence  in  the 
other,  are  the  cause  of  the  difference  in  the  color  of  the  sandstones. 
Coal-measure  sandstones  are  white  or  gray,  being  leached  of  their 
oxide  of  iron  by  organic  matter.  Salt- measure  sandstones  are  usually 
red,  the  iron  being  diffused  as  coloring-matter. 

Theory  of  Accumulation. — We  have  already  seen  (p.  80)  that  salt- 
lakes  are  evaporated  residues  of  river-water  or  sea-water  in  dry  cli- 
mates, and  are  now,  most  of  them,  depositing  salt ;  also,  that  sea- 

*  American  Journal  of  Science,  vol.  v,  p.  362,  1873. 
f  Bischof,  Chemical  Geology,  vol.  i,  p.  383. 
\  Nature,  vol.  xv,  p.  240,  1877. 


ORIGIN  OF  ROCK-SALT.  423 

water  evaporated  deposits  first  gypsum,  then  salt :  also,  that  these  de- 
posits of  salts  and  gypsum  alternate  annually  with  sediments  of  sand 
and  clay — the  salt  or  gypsum  deposit  representing  the  dry  season,  and 
the  mechanical  deposits  representing  the  season  of  floods.  It  is,  there- 
fore, natural  to  look  in  this  direction  for  an  explanation  of  salt  and 
gypsum  deposits — to  think  that  salt-basins  are  dried-up  salt-lakes. 
But  the  immense  thickness  of  the  beds  plainly  shows  that  there  must 
have  been  important  modifications  of  this  process.  It  is  plain  that 
the  alternations  of  salt  and  sedimentary  deposit  were  not  annual  but 
secular. 

The  conditions  under  which  salt-measures  were  formed  are  not  cer- 
tainly known,  but  most  probably  they  are  a  dry  climate,  a  low  coast, 
with  bordering  salt  lagoons  or  bays,  partly  cut  off  from  the  sea  by 
bars,  subject  to  intense  evaporation,  and  resupplied  with  salt-water  by 
tides  or  by  winds,  or  perhaps  at  longer  intervals  by  crust-movements. 
It  is  easy  to  imagine  how  salt-measures  with  their  alternation  of  gyp- 
sum, salt,  and  sediments,  may  thus  have  been  formed.  We  have  ex- 
amples of  the  process  now  going  on,  on  the  east  shore  of  the  Caspian 
Sea,  where  salt  has  been  depositing  for  ages,*  even  though  the  water 
ol  the  Caspian  is  much  fresher  than  that  of  the  ocean.  On  the  other 
hand,  it  seems  to  us  that  the  recent  observations  of  Gilbert  and  Rus- 
sell on  the  deposits  of  the  great  dried-up  lakes  Lahontan  and  Bonne- 
ville  of  the  Basin  region  (p.  565)  throw  much  light  on  this  subject,  and 
that  in  the  phenomena  of  these  deposits  we  probably  have  at  least  an 
additional  method  in  which  salt-measures  may  be  formed.  There  is 
abundant  evidence  that  these  lakes  have  filled  and  dried  up  and  left 
beds  of  salt,  more  than  once,  and  that  at  each  refilling  the  lake  com- 
menced as  a  fresh  lake.  The  process  was  briefly  as  follows  :  The  great 
lake,  at  first  fresh,  gradually  became  saline  and  finally  dried  away, 
leaving  a  thick  bed  of  salt.  This  salt-bed  was  then  covered  by  the 
washing  in  of  fine,  impervious  clay,  and  thus  protected  from  re-solution 
when  the  lake  reformed.  This  process  was  repeated  in  the  case  of  Lake 
Lahontan  three  times — that  is,  there  are  now,  beneath  the  salt-lakes  of 
this  region,  two  beds  of  salt  separated  by  clay,  and  the  third  deposit  is 
now  forming.  Salt-beds  are  now  reached  and  worked  in  many  places 
of  this  region  by  penetrating  the  fine  clay  which  marks  the  places  of 
the  old  lakes,  f 

In  the  deposits  of  salt-lakes  or  saturated  lagoons  we  would  not  ex- 
pect to  find  many  animal  remains,  but  the  tracks  of  animals  along  their 

*  Ochsenius,  Proceedings  of  the  Academy  of  Natural  Sciences,  Philadelphia,  1888, 
p.  181. 

f  Gilbert,  Lake  Bonneville,  Wheeler's  Survey,  vol.  iii ;  American  Journal  of  Science, 
vol.  xxxi,  p.  354, 1886  ;  Russell,  Lake  Lahontan,  Monograph  of  United  States  Geological 
Survey,  vol.  xi. 


424: 


MESOZOIC  ERA— AGE  OF  REPTILES. 


muddy  shores,  as  also  sun-cracks  and  rain-prints,  would  be  found  as  on 
other  shores.  Now,  although  in  the  strata  associated  with  salt  organic 
remains  are  rare,  shore-marks  of  all  kinds  are  common.  Thus  de- 
posits of  gypsum  and  salt  may  be  taken  as  evidence  of  dry  climate. 


SECTIOK  2. — JURASSIC  PERIOD. 

This  is  the  culminating  period  of  the  Mesozoic  era  and  Eeptilian 
age.  In  it  all  the  characteristics  of  this  age  reach  their  highest  de- 
velopment. We  must  discuss  this  somewhat  more  fully  than  the  last. 

The  strata  belonging  to  this  period  are  magnificently  developed  in 
the  Jura  Mountains,  and  hence  the  name  Jurassic.  These  mountains 
are  an  admirable  illustration  of  the  manner  in  which  ridges  and  valleys 

are  formed  by  the  f old- 


626) ;  they  also  abound 
in  fossils  of  this  pe- 
riod. 

English  geologists 
call  the  period  Oolite 
(egg-stone)  on  account 
of  the  abundant  oc- 
currence in  that  coun- 
try of  a  peculiar  limestone  composed  often  wholly  of  small,  rounded 
grains  like  the  roe  of  a  fish.  They  divide  the  whole  period  into  three 
epochs,  viz. :  1.  Lias;  2.  Oolite  proper  ;  3.  Wealden.*  They  also  sub- 
divide the  Oolite  proper  into  Loiver,  Middle,  and  Upper  Oolite,  sepa- 


FIG.  626.— Section  of  the  Jura  Mountains. 


Lower 
OSlite. 


Middle 
OSlite. 


Upper 
OOlite. 


London 
Chalk.     Clay. 


Lias. 


Oxford  Clay. 
FIG.  627. 


Kimmeridge     Gaulu 
Clay. 


rated  by  intervening  Oxford  and  Kimmeridge  clays.  All  these  divis- 
ions and  subdivisions  are  well  shown  in  the  following  section  passing 
from  London  westward.  This  section  is  interesting  not  only  as  exhib- 
iting all  the  divisions  and  subdivisions  of  the  Oolitic  period,  but  also 
as  showing  their  conformity  among  themselves  and  with  the  overlying 
chalk,  and  the  unconformity  of  these  with  the  overlying  Tertiary.  It 
also  shows  how  parallel  ridges  and  intervening  hollows  are  formed  by 
the  outcroppings  of  a  series  of  strata  alternately  hard  and  soft. 

Origin  of  Oolitic  Limestones. — These  are  composed  of  rounded  grains 
with  concentric  structure.     We  have  already  seen,  page  156,  that  on 


*  The  Wealden  is  now  often  put  in  the  Cretaceous. 


JURASSIC  PERIOD.  425 

coral  shores  a  kind  of  sand  is  formed  by  the  action  of  waves  on  frag- 
ments of  coral  and  shells.  These  fragments  are  rounded  by  attrition ; 
then  often  enlarged  by  deposit  of  concentric  layers  of  lime  from  the 
saturated  sea- water ;  and,  finally,  cemented  by  the  same  into  hard  rock. 
In  some  such  way  oolitic  limestones  have  been  formed  in  all  geological 
periods.  We  conclude,  therefore,  that  in  Jurassic  times  great  coral 
reefs  existed  where  England  now  stands.  In  the  Jura  Mountains  it  is 
believed  that  the  remains  of  fossil  circular  reefs  or  atolls  of  this  period 
are  still  detectable  (Heer). 

Jurassic  Coal-Measures. — In  the  Jurassic  times  we  have  reproduced 
on  a  large  scale  the  conditions  favorable  to  luxuriant  growth  of  plants, 
and  for  their  accumulation  and  preservation  in  the  form  of  coal. 
Hence  in  many  countries  we  have  Jurassic  coal-fields.  To  this  period 
belong  the  Yorkshire  coal  of  England  and  the  Brora  coal  of  Scotland. 
To  this  or  the  previous  period  belong  the  coal-fields  of  North  Carolina 
and  Eastern  Virginia,  and  some  of  the  coal-fields  of  India*  and  China. 
The  fine  coal-measures  of  New  South  Wales,  Australia,  covering  an 
area  of  20,000  square  miles,  are  partly,  though  not  mainly,  Jurassic  or 
Triassic,  as  are  also  those  of  South  Africa.  Jurassic  coal-measures  have 
a  general  structure  similar  to  those  of  the  Carboniferous.  Like  the 
latter,  they  consist  of  alternations  of  sands  and  clays,  and  occasional 
limestones,  containing  seams  of  coal  and  beds  of  iron-ore.  The  iron- 
ore  too  is  of  the  same  kind,  viz.,  clay  iron-stone.  We  find  here  also 
under-clays,  with  stumps  and  roots,  and  roof-shales  filled  with  leaf- 
impressions.  It  is  fair  to  conclude,  therefore,  that  the  mode  of  accu- 
mulation was  similar  to  that  already  described,  viz.,  in  marshes  subject 
to  occasional  floods,  Jurassic  coal,  though  perhaps  inferior  as  a  general 
rule  to  Carboniferous,  is  often  of  good  quality,  occurring  in  thick  and 
profitable  seams. 

Dirt-Beds — Fossil  Forest-Grounds. —  Coal-seams  with  their  under- 
lying clays  are  fossil  swamp-grounds  ;  dirt-beds  are  fossil  soils  or  forest- 
grounds.  The  one  graduates  insensibly  into  the  other,  and  both  are 
occasionally  found  in  all  strata,  from  the  Devonian  upward.  In  the 
Upper  Oolite  of  England,  at  the  Isle  of  Portland  and  elsewhere,  there 
occurs  an  interesting  example  of  such  a  fossil  forest-ground  with  the 
erect  stumps  and  ramifying  roots  still  in  situ,  though  silicified,  and 
the  logs,  also  silicified,  still  lying  on  the  fossil  soil  (Figs.  628,  629).  It 
is  evident  that  the  sequence  of  events  at  this  place  in  Jurassic  times 
was  as  follows :  1.  The  place  was  sea-bottom,  and  received  sediment 
which  consolidated  into  Portland-stone.  2.  After  being  flooded  and 
covered  with  river-deposit,  it  was  raised  to  land  and  became  forest- 

*  The  plant-beds  of  India  (Gondwana  series  of  Indian  geologists)  are  Permian  to  Ju- 
rassic inclusive. — (Manual  of  Indian  Geology  p.  102  et  seq.) 


426 


MESOZOIC  ERA— AGE   OF  REPTILES. 


ground,  covered  with  trees  and  other  vegetation  peculiar  to  that  time, 
the  decaying  leaves  of  which  accumulated  as  a  rich  and  thick  vegetable 


FIG.  628.— Section  in  Cliff  east  of  Lul- 
worth  Cove:  a,  Dirt-bed. 


FIG.  629.— Section  in  the  Isle  of  Portland: 
a,  Dirt-bed. 


Fia.  630.— Zamia  spiralis,  a  Living  Cycad  of  Australia. 


mold.     3.  It  became  flooded  with  fresh  water,  and  the  trees  therefore 
died  and  rotted  to  stumps.     4.  The  whole  ground,  with  its  stumps  and 
logs,  became  covered  with  mud,  which  hardened  into  slates.     5.  Fi- 
nally,    the    whole    was 
raised   into    high  land, 
and   in   the   first  figure 
(Fig.    628)   tilted    at    a 
considerable  angle. 

Thus,  we  have  here 
not  only  an  old  forest- 
ground  with  its  vegeta- 
ble mold,  but  also  the 
stumps  and  logs  of  the 
trees  which  grew  there, 
still  in  place ;  and  closer 
examination  easily  detects  the  kinds  of  trees  which  grew  in  the  forest. 
They  are  Cycads  and  Conifers  (Figs.  630,  631  and  635-638).  Still  fur- 
ther, there  is  good  reason  to  believe  that  the  remains  of  some  of  the 
animals  which  roamed  these  forests  have  also  been  found.  Of  these 
we  will  speak  in  their  proper  place. 

Plants. 

Although  the  conditions  under  which  coal  was  accumulated  were 
probably  similar  in  all  geological  periods,  yet  the  kinds  of  plants  out  of 
which  the  coal  was  made  varied.  As  already  seen,  the  principal  coal- 
plants  of  the  Carboniferous  period  were  vascular  Cryptogams.  On  the 
contrary,  the  principal  coal-plants  of  the  Jurassic  period  were  Ferns, 
Cycads,  and  Conifers.  The  Jurassic  may  be  called  the  age  of  Gym- 
nosperms,  as  the  Carboniferous  was  the  age  of  Acrogens.  The  Gym- 
nosperms,  especially  the  family  of  Cycads,  reached  here  their  highest 
development.  This  is  shown  in  diagram  on  page  283.  The  leaves 
(Fig.  631)  and  short  stems  of  Cycas  and  Zamia  (Fig.  638)  are  found 


JURASSIC  PLANTS. 


427 


FIG.  631. 


Fio.  633. 


FIG.  634. 


FIG.  635. 


FIG.  636. 


Fios.  631-688.— JURASSIC  PLANTS- Cycads  and  Ferns:  631.  Pterophyllnm  comptum  (a  Cycad).  632. 
Hemitelites  Brownu  (a  Fern).  633.  Coniopteris  Murrayana.  634.  Pachypteris  lanceolata.  Con- 
ifers :  635.  Cone  of  a  Pine.  636.  Cone  of  an  Araucaria. 

very  abundantly  in  connection  with  the  coal-bearing  strata.  It  is  prob- 
able, therefore,  that  the  coal  is  composed  largely  of  these  plants.  Some 
remains  of  Jurassic  plants  are  given  (Figs.  631-636),  and  also  of  living 
Cycads  (Figs.  630,  637),  for  comparison. 


428 


MESOZOIC   ERA— AGE   OF  REPTILES. 


Animals. 

The  animals  of  the  Jurassic,  marine,  fresh-water,  and  land,  were 
very  abundant,  and  have  been  well  preserved.  It  is  impossible,  there- 
fore, in  the  lower  departments, 
to  do  more  than  touch  lightly 
the  most  salient  points.  In 
the  higher  departments  we  will 
dwell  a  little  longer. 

Corals  have  assumed  now 
the  modern  type  and  style  of 
partitions  (Fig.  639).  Among 


FIG.  637. — Cycas  circinalis,  x  T|r,  a  Living  Cycad  of  the      FIG.  638. — Stem  of  Cycadeoidea  megalo- 
Moluccas  (after  Decaisne).  phylla,  x  £. 

EcMnoderms,  the  Crinids,  or  plumose-armed  Crinoids,  are  very  abun- 
dant and  very  beautiful ;  in  fact,  they  seem  to  have  reached  their  high- 
est point  in  abundance,  diversity,  and  gracefulness  of  form  (Figs.  640, 
641).  But  the  free  forms,  Echinoids  and  Asteroids,  are  now  equally 
abundant  (Figs.  642-644). 

BracMopods  are  still  abundant,  though  far  less  so  than  formerly ;  but 
they  now  belong  almost  wholly  to  the  modern  or  sloping-shouldered 
types,  such  as  Terebratula  and  Khynchonella.  Only  a  very  few  small 
specimens  of  the  Palaeozoic  type  linger  until  the  Lias. 

Lamellibranchs,  or  common  bivalves,  are  extremely  abundant. 
Among  the  common  and  characteristic  forms  are  Trigonia,  Cfryphasa, 
and  Exogyra,  belonging  to  the  oyster  family ;  and  the  strangely-shaped 
Diceras  (Fig.  645).  It  is  interesting,  also,  to  observe  here  the  first 
appearance  of  the  genus  Ostrea  (oyster). 

Cephalopods. — One  of  the  most  striking  characteristics  of  the  Juras- 
sic period  is  the  culmination  of  the  class  of  Cephalopods  in  number , 
diversity  of  forms,  and,  if  we  except  some  of  the  Silurian  Orthocera- 
tites,  in  size.  They  were  represented  by  the  Ammonites  and  the  Be- 
lemnites,  the  one  belonging  to  the  order  of  Tetrabranchs,  or  shelled, 
the  other  to  the  Dibranchs,  or  naked  Cephalopods.  It  is  important  to 


JURASSIC  ANIMALS. 


FIG.  640. 


FIG.  642. 


FIG.  644. 


FIGS.  639-644.— JURASSIC  CORALS  AND  ECHINODE RMS:  639.  Prionastrea oblongata.  640.  Apiocrinus 
Roissianus.  (541.  Saccocoma  pectinata(a  free  Crinoid).  642.  Asteria  lombricalis.  643.  Clypeus 
Plotii.  644.  a  b,  Hemicidaris  crenularis. 

observe  that  the  highest  order  of  Cephalopods,  the  Dibranchs,  by  far 
the  most  abundantly  represented  at  the  present  time,  were  introduced 
here  for  the  first  time. 


FIG.  646. 


FIG.  647. 


FIG.  645. 


FIGS.  645-647.— JURASSIC  LAMELLIBRANCHS  AND  BRAcmopong 
OF  ENGLAND:  645.  Diceras  Arietina,  Middle  OCHte  (after 
Nicholson).  646.  Aetarte  excavata.  647.  Trigonia  cla- 
vellata. 


430 


MESOZOIC  ERA— AGE   OF  REPTILES. 


FIG.  652. 


FIG.  653. 


Flo.  650. 


FIG.  651. 


FIGS.  648-653. — JURASSIC  LAMELLIBRANCHS  AND  BRACHIOPODS  OF  ENGLAND:  648.  Ostrea  Sowerbyi. 
649.  Pecten  fibrosus.  650.  Ostrea  Marshii.  651.  Rhynckonella  varians.  652.  Terebratula  sphse- 
roidalis.  653.  Terebratula  digona  (after  Nicholson). 

Ammonites. — The  Ammonite  family,  which  is  distinguished,  as 
already  explained  (p.  '3'l'S,),  by  the  dorsal  position  of  the  siphuncle 
and  the  complexity  of  the  suture,  is  represented  in  extreme  abun- 
dance by  the  type- 
genus  Ammonites.  * 
About  500  species 
of  this  genus  are 
known,  ranging  in 
time  from  the  Trias- 
sic  through  the  Cre- 
taceous. They  are 
therefore  character- 
istic of  the  Meso- 
zoic.  They  varied 
extremely  in  shape, 
and  in  size  from  half 
an  inch  to  a  yard  or 
more  in  diameter.  The  accompanying  figures  represent  some  of  the 
most  common  species. 

In  the  genus  Ammonites  the  distinguishing  character  of  the  family, 
viz.,  the  complexity  of  the  suture,  reached  its  highest  point.  In  this 
genus,  the  edge  of  the  septa,  which  was  only  zigzag  in  Groniatite,  and 
lobed  in  the  Ceratite,  becomes  most  elaborately  frilled.  We  give  in 
Fig.  659  the  form  of  suture  in  the  type-genera  of  the  different  orders 
of  shelled  Cephalopods,  in  the  order  of  their  first  appearance.  In  each 


FIG.  654.— Ammonites  Humphreysianus. 


*  This  genus  is  now  broken  up  into  many,  but  it  is  still  convenient  to  retain  the  name 
for  a  very  distinct  group  of  Cephalopods. 


JURASSIC   ANIMALS. 


431 


case  the  suture  is  supposed  to  be  divided  on  the  ventral  surface  and 
spread  out,  so  that  the  central  part  in  the  figure  represents  the  dorsal 


FIG.  657.  Fio.  658. 

Fies.  655-658. — JURASSIC  CEPHALOPODS — Ammonites:  655.  Ammonites  bifronp.  656.  Ammonites 
margaritanue.  657.  Ammonites  Jason:  a,  side  view;  b,  showing  suture.  658.  Ammonites  cor- 
datus:  a,  side  view;  b,  showing  suture. 

portion,  and  the  two  extremities  the  ventral.     The  evolution  of  form 
»and  structure  was  in  the  following  order :  First  the  straight  Ortlioceras, 

Ammonite. 


W   \ 


Ceralite. 


0 


NautUoids, 


Orthoceratite. 


Fis.  659.— Diagram  showing  Form  of  the  Suture,  Position  of  Siphuncle,  and  Order  of  First  Appear- 
ance of  Families  in  Cephalopods. 


432 


MESOZOIC  ERA— AGE  OF  KEPTILES. 


then  the  curved  Gyroceras,  then  the  coiled  Nautiloids,  then  the  simple 
suture  became  angled  in  Goniatite,  then  scalloped  in  Ceratite,  and 
finally  complexly  frilled  in  Ammonite.  It  is  remarkable,  however,  that 
one  of  the  simpler  forms,  viz.,  the  nautiloids,  although  also  one  of  the 
earliest,  has  outlived  them  all.  The  corresponding  figures  on  the  left 
are  sections  showing. the  position  of  the  siphuncle. 

The  order  in  which  these  several  genera  appeared,  and  their  contin- 
uance, are  shown  in  the  diagram  (Fig.  669)  on  page  434. 

Belemnites. — The  Belemnite  (/2e'Ae/xvov,  a  dart)  was  nearly  allied  to 
the  squid  and  cuttle-fish  of  the  present  day.     Like  the  squid,  it  had  an 

internal  bone  (the  pen  of  the 
squid),  except  that  the  bone  is 
much  larger  and  heavier  in  the 
Belemnite.  It  is  this  bone,  or 
the  lower  portion  of  it,  which  is 
usually  fossilized  (Figs.  664-667). 
When  perfect  it  is  expanded  and 
hollow  at  the  upper  end,  and  in 
the  hollow  is  a  small,  conical, 


FIG.  660.  FIG.  661.  FIG.  662. 

FIGS.  600-662.— 660.  Internal  Shell  of  Belemnite  (restored  by  D'Orbigny).   661.  The  Animal  (restored 
by  Owen).    662.  A  living  Sepia  for  comparison. 

chambered,  siphuncled  shell,  the  Phragmocone.  Fig.  660,  a  and  #, 
shows  the  perfect  bone,  and  Fig.  664  the  upper  part  broken  and  the 
phragmocone  in  place.  Like  the  squid,  too,  it  had  an  ink-bag,  from 
which  it  doubtless  squirted  the  inky  fluid  to  darken  the  water  and 


JURASSIC  ANIMALS. 


433 


escape  its  enemy.  These  ink-bags  are  often  well  preserved  (Fig.  663), 
and  the  fossil  ink  has  been  found  to  make  good  pigment  (sepia),  and 
drawings  of  these  extinct  animals  have  actually  been 
made  with  the  fossil  ink  of  their  own  ink-bags 
(Buckland).  Belemnites  were  some  of  them  of 
great  size,  and  evidently  formidable  animals.  The 
bone  of  the  Belemnites  giganteus  has  been  found 
two  feet  long  and  three  to  four  inches  in  diameter 
at  the  larger  or  hollow  end.  A  very  perfect  speci- 
men of  an  allied  genus,  from  the  Oolite  of  England, 
is  shown  in  Fig.  668. 


FIG.  663. 


FIG.  664. 


FIG.  667. 


FIGS.  663-668.— 663.  Fossil  Ink-Bags  of  Belemnites.  664.  Belemnites  Owenii.  665.  Belemnites  has- 
tatus.  666.  Belemnites  unicanaliculatus.  667.  Belemnites  clavatus.  668.  Acanthoteuthis  anti- 
quus  (after  Mantell). 

The  following  diagram  shows  the  order  of  succession  of  families  of 
the  class  Cephalopoda : 
28 


MESOZOIC  ERA— AGE   OF  REPTILES. 


PALAEOZOIC. 

NEOZOIC. 

MESOZOIO. 

CKNOZOIO. 

Sil'n. 

Dev'n. 

Carb. 

Trias. 

Juras. 

Cret. 

Tert. 

Pres. 

Cepha 

lopods. 

Shelled 

or  Tetral 

)ranchs. 

Nake 

d     or 

[)  i  b  r  a  i 

i  c  h  s  . 

Shi 

lied. 

0  r  t  h  < 

>ceratites. 

N 

a 

u 

t 

i 

1           0 

i 

d     s  . 

G 

oniatites. 

Ceratites. 

A  m 

m  o  n  i  1 

,  e  s  . 

Na 

Iced. 

B  e  1  e  m 

n  i  t  e  s  . 

S   e   p 

i   a. 

FIG.  669.— Diagram  showing  Distribution  of  Cephalopods  in  Time. 


Crustacea, — Crustacea  were  rep- 
resented in  the  Palaeozoic  first  by 
the  Trilobites ;  then  Eurypterids ; 
then  Limuloids  ;  then,  in  the  last 
period,  by  a  few  Macrourans.  In 
the  Triassic  the  Macrourans  be- 
came more  abundant  and  of  more 
modern  type.  In  the  Jurassic  the 
Macrourans  continue,  with  also 
many  Limuloids,  but  the  former 


FIG.  670. 


FIG.  671. 

FIGS.  670,  671.— JURASSIC  CRUSTACEANS:  670. 
Eryon  arctiformis,  Solenhofen.  671. 
Eryon  Barrovensis,  England. 


JURASSIC   ANIMALS. 


435 


make  here  a  decided  approach  to  the  Brachyourans  or  true  crabs,  by 

the  shortening  of  the  tail  in  some  (Fig.  670) ;  and  the  earliest  true 

crab,    Palaeinachus 

— a  spider-crab — 

lias  been  found  in 

the      Jurassic     of 

England.  The 

same  change — i.  e., 

shortening  of    the 

tail — may  be  seen 

in   the    embryonic 

development   of    a 

crab  (Fig.  672). 

Insects.  -  -  As 
might  be  expected 
from  the  abundant 

forest       Vegetation,  FIG.  672.— Development  of  Carcinus  mtenas:  A.  zooea  stage;  B,  mega- 
insects     have    been  lopa  stage;  C,  final  state  (after  Couch). 

found  in  considerable  numbers  and  variety  (Figs.  673-678).     Accord- 
ing to  Heer,  143  species  of  insects  are  known  from  the  Lias  alone. 


FIG.  678. 


FIG.  676. 


FIGS.  673-678.- JURASSIC  INSECTS  :  673.  Blattina  formosa  (after  Heer).    674.  Glaphyroptera  gracilis 
ffide?T a'nteu  eximia  (Hager)     676.  Libellula.    677.  Buprestidium.    678.  Hemero- 


436 


MESOZOIC  ERA— AGE   OF  REPTILES. 


Of  these,  about  three  fourths  are  beetles.  The  earliest  of  the  higher 
group  of  insects  seem  to  have  been  introduced  here,  although  they  do 
not  become  abundant  until  the  Tertiary. 

Fishes. — It  will  be  remembered  that  the  Placoids  of  the  Palasozoic 
were  nearly  all  Cestracionts,  or  crushing-toothed  sharks.     The  Hybo- 


FIG.  682. 

FIGS.  679-682.— JURASSIC  PISHES — Placoids:  679.  Tooth  of  Acrodus  nobilis.  680.  Hybodus  reticu- 
latus.  Spine  and  Tooth.  681.  Squatina  acanthoderma.  682.  Ganoid :  Tetragonolepis,  restored, 
and  Scales  of  the  same. 

donts,  or  sharks  with  teeth  pointed,  but  rounded  on  the  edges,  com- 
menced in  the  Carboniferous  and  increased  in  the  Triassic.  Now,  in 
the  Jurassic  the  Cestracionts  continue  (Fig.  679),  but  in  diminished 
numbers.  The  Hybodonts  culminate  (Fig.  680),  and  the  Squalodonts, 
or  modern  sharks,  with  lancet-shaped  teeth,  commence  in  small  num- 
bers. Ra'ys  (Fig.  681),  which  may  be  regarded  as  among  the  highest  of 
Placoids,  are  found  in  considerable  numbers  in  the  Jurassic. 

Ganoids  continue,  but  take  on  far  more  modern  forms,  and  have 
now  in  most  cases  lost  the  vertebrated  structure  of  the  tail-fin,  thus 
foreshadowing  the  Teleosts,  which  appear  in  the  next  period.  Among 
the  most  characteristic  Ganoids  of  this  period,  and,  in  fact,  of  this  age, 
are  the  Pycnodonts,  a  family  characterized  by  a  broad,  flat  body,  rhom- 


JURASSIC  ANIMALS. 


437 


boidal  enameled  scales,  pavement  palatal  teeth,  and  persistent  noto- 
chord  (Fig.  682). 

Reptiles. — The  huge  reptiles  which  form  the  distinguishing  feat- 
ure of  this  age  culminate  in  the  Jurassic  period.  Their  number  and 
variety  are  so  great  that  we  can  only  select  a  few  from  each  order  for 


Fio.  685. 


FIG.  686. 


FIGS.  683-686.— JURASSIC  REPTILES— Ichthyosaurus  and  Plenosaurus :  683.— Ichthyosaurus  coramu- 
nis,  x  Tfoj.  684.  Plesiosaurus  dolichodeirus,  restored,  x  Jg.  685.  Vertebrae  of  Ichthyosaurus  and 
Section  of  same,  showing  structure.  686.  Tooth  of  Ichthyosaurus,  natural  size. 

description.  They  were  emphatically  rulers  in  every  department  of 
Mature — rulers  of  the  sea,  of  the  land,  and  of  the  air.  We  shall  treat 
of  them  under  the  three  heads  thus  indicated,  viz. :  1.  Enaliosaurs 
(sea-saurians),  or  rulers  of  the  sea ;  2.  Dinosaurs  (huge  saurians),  or 
rulers  of  the  land ;  and,  3.  Pterosaurs  (winged  saurians),  or  rulers  of 
the  air.  The  first  were  wholly  swimming,  the  second  walking,  the 
third  flying,  saurians.  Intermediate  between  the  first  and  second  was  a 
fourth  order,  the  Crocodilians,  which  both  swam  and  crawled. 

1.  Enaliosaurs. — From  the  immense  variety  of  these  we  select  only 
two  for  description  as  representative  genera,  viz.,  Ichthyosaurus  and 
Plesiosaurus  (Figs.  683  and  684). 

The  Ichthyosaurus  (fish-lizard)  was  a  huge  animal,  in  some  cases 
thirty  to  forty  feet  in  length,  with  a  stout  body,  short  neck,  and  enor- 
mous head,  sometimes  five  feet  long,  and  jaws  set  with  large  conical, 
striated  teeth,  sometimes  200  in  number.  The  enormous  eyes,  some- 
times fifteen  inches  in  diameter,  were  provided  with  radiating,  bony 
plates  (sclerotic  bones),  as  are  the  eyes  of  birds  and  some  living  and 


438 


MESOZOIC  ERA— AGE  OF  REPTILES. 


many  extinct  reptiles,  apparently  for  adjusting  the  eye  to  different  dis- 
tances. The  tail  was  long,  and  probably  provided  terminally  with  a 
vertical,  fin-like  expansion,  unsupported  by  rays  (Owen).  In  addition 
to  the  powerful  fin-tipped  tail,  the  locomotive  organs  were  four  short 
stout  paddles,  composed  of  numerous  closely-united  bones,  but  without 
distinct  toes.  These  paddles  were  surrounded  by  an  expanded,  ray- 
supported  web  (Fig.  687),  which  greatly  increased  their  surface,  and 
therefore  their  efficiency  as  swimming-organs  (Lyell).  The  bodies  of  the 
vertebrae  were  not  united  by  ball-and-socket  joint,  as  in  most  living  rep- 
tiles, but  were  bi-concave  (amphiccelous),  like  those  of  fishes  (Fig.  685). 

That  the  habits  of 
the  creature  were  preda- 
tory and  voracious  is 
sufficiently  attested  by 
the  teeth.  It  is  further 
proved  by  the  contents 
of  the  stomach,  which 
are  sometimes  partly 
preserved.  These  con- 
sist largely  offish-scales. 
From  the  descrip- 


FIG.  687,-Paddle-Web  of  an  Ichthyosaurus. 


gyen 


g 


plain  that  the  Ichthyosaurus  combined  in  a  remarkable  degree  the 
characters  of  saurian  reptiles  with  those  of  fishes.     The  vertically-ex- 
panded tail-tip,  the  paddles,  with  surrounding  ray-supported  web,  and 
the  bi-concave  vertebral  bodies,  are  all  decided  fish 
characters.     In  most  other  respects  it  was  reptilian. 
This  combination  is  expressed  in  the  name. 

The  Plesiosaurus  (allied  to  a  lizard)  was  a  less 
heavy  and  powerful  animal  than  the  last.     It  was  re- 


Fio.  688.— a,  Head  of  a  Pliosanrus,  greatly  reduced;  ft,  Tooth  of  the  same,  natural  size. 

markable  for  its  short,  stout,  almost  turtle-shaped  body;  its  long, 
snake-like  neck,  consisting  of  twenty  to  forty  vertebra? ;  its  small  head ; 
its  short  tail,  unadapted  for  powerful  propulsion ;  its  long  and  powerful 
paddles,  which  were  its  sole  swimming-organs ;  and  its  bi-concave  ver- 


JURASSIC  ANIMALS. 


439 


tebral  bodies.  Recent  discoveries  in  Kansas  show  that  sclerotic  bones 
were  present  in  this  order  also.*  Sixteen  species  have  been  found  in 
the  Jurassic  and  Cretaceous  rocks  of  Great  Britain  alone,  and  one,  P. 
dolichodeirus,  was  twenty-five  to  thirty  feet  long  (Fig.  684),  with  pad- 
dles six  to  seven  feet  long. 

The  Pliosaurus  (more  lizard-like)  had  the  large  head  and  short 
neck  of  the  Ichthyosaurus  (Fig.  G88),  with  the  powerful  paddles  of  the 


FIG.  689.— Paddle  of  a  Pliosaurus,  x  &. 

Plesiosaurus.  A  perfect  paddle  of  this  animal  has  been  found  seven 
feet  long  (Fig.  689) ;  the  animal  was  probably  at  least  forty  feet  long. 

Intermedi- 
ate between  this 
group  and  the 
next — inhabit- 
ers  both  of 
land  and  water 
—  Crocodilians 
existed  in  great 

FIG.  690.— Teleosaurus  brevidens:  a,  skull;  b,  side  view  of  snout  showing      numbers,       and 
the  teeth  (after  Phillips).  of      greafc     ^ 

Some,  like  the  Teleosaurus  (Fig.  690),  were  narrow-snouted  like  the  Ga- 
vials  of  the  Ganges,  but  had  amphiccelous  vertebrae  like  the  Enaliosaurs. 

2.  Dinosaurs. — Among  these  were  the  largest  reptiles — in  fact,  the 
largest  land-animals — that  have  ever  existed.  They  were  also  in  many 
respects  the  highest  of  all  reptiles,  since  they  possessed  many  charac- 
ters which  connected  them  closely  with  mammals,  and  especially  with 
birds. 

Connecting  Characters. — The  most  important  of  these  were:  (1.) 
Large,  hollow  limb-bones  and  firm  sacrum  composed  of  several  consoli- 
dated vertebras.  These  characters  show  that  these  animals  walked  with 
a  free  step,  the  body  well  borne  above  the  ground,  like  mammals  and 
birds,  and  did  not  crawl  in  the  manner  of  reptiles.  (2.)  In  many  cases 
the  hind-legs  were  very  large  and  long,  and  the  fore-legs  very  small  in 
comparison.  This,  together  with  the  backward  elongation  of  the 
ischium  (Fig.  691  B) — suitable  for  erecting  the  body — show  that  some 

Williston,  Science,  vol.  16,  p.  262, 


440 


MESOZOIC   ERA— AGE   OF   REPTILES. 


of  them  walked  habitually  on  their  hind-legs  alone,  in  the  manner  of 
birds.  (3.)  Like  birds  and  some  mammals,  many  Dinosaurs  tread  on 
their  toes  (digitigrade)  and  not  like  reptiles  on  the  whole  foot  (planti- 
grade). (4.)  Like  birds,  also,  many — but  not  all — had  only  three  func- 
tional toes,  and  therefore  made  tridactyle  tracks ;  and  even  the  number 
of  toe-joints  follows  the  order  of  those  of  birds— i.  e.,  there  were  three 
in  the  inner  toe,  four  in  the  middle,  and  five  in  the  outer  toe.  (5.) 
Still  more  curious  is  the  resemblance  to  birds,  in  the  structure  of  the 


FIG.  691. — J.,  Dromaeus;  B,  Dinosaur;  (7,  Crocodile:  As,  astragulus;  Ca,  calcaneum, 

ankle-joint.  In  reptiles — as  also  in  mammals— the  joint  is  between 
the  shank-bones  and  the  tarsus ;  in  birds,  the  astragalus  and  calca- 
neum are  consolidated  with  the  shank,  and  the  motion  is  below  these 
bones  of  the  tarsus.  Some  Dinosaurs  are  like  birds  in  this  regard. 
Fig.  691,  ABC,  illustrates  this  point.  (6).  Many  Dinosaurs  pos- 
sessed a  clavicle — a  bone  found  in  all  birds  and  many  mammals,  but  no 
living  reptile.  We  shall  very  briefly  describe  only  the  most  re- 
markable. 

The  Iguanodon  was  one  of  the  best  known  as  well  as  one  of  the 
largest.  It  was  a  huge  herbivorous  Dinosaur,  found  in  the  Upper 
Jurassic  and  Lower  Cretaceous  of  Europe.  It  takes  its  name  from  the 
resemblance  of  its  teeth  (Fig.  692)  to  those  of  an  Iguana — a  living 
herbivorous  reptile,  about  four  or  five  feet  long,  although  in  other 
respects  there  is  little  affinity.  Until  recently,  only  portions  of  the 
skeleton  were  found ;  but  the  enormous  size  of  these  indicated  an  ani- 
mal at  least  thirty  feet  long,  and  several  times  the  weight  of  an  ele- 


JURASSIC  ANIMALS. 


441 


Fie.  692.— Tooth  of  an  Iguanodon. 


phant.     It  was  impossible  from  these  to  form  any  idea  of  its  general 

appearance.     In  1880,  however,  several  complete  skeletons  were  found 

in  Belgium  and  restored 

by  Dollo.     From  these  it 

is  learned  that  the  animal 

certainly   walked    on    its 

hind-legs,  using  its  power- 

ful tail  also  as  a  support  ; 

also  that  the  anterior  part 

of  its  jaws  was  toothless 

and  covered  with  horn,  so 

as  to  form  a  nipping-beak 

like  a  turtle's.    Fig.  693  is 

a  restoration  by  De  Pauw. 
The    Megalosaur  was 

a   somewhat   smaller  but 

probably  a  more  formida- 

ble   carnivorous    reptile, 

which  lived  through  the  whole  Jurassic  period.     Its  huge  jaws  were 

armed  with  large,  curved,  flattened,  saber-like  teeth.  A  femur  has  been 
found  forty-two  inches  long  (Phillips),  and  a  tibia 
thirty-six  inches.  The  animal  was  at  least  thirty  feet 
long  (Owen).  Fig.  694  is  a  restoration  of  the  head  of 
this  animal  by  Phillips,  and  Fig.  695  is  a  restoration 

of  the  skeleton  of 
the  Scelidosaurus, 
an  animal  allied  to 
the  Megalosaur. 
The  Megalosaurs 
also  were  bipedal, 

The  Ceteosaur 
(whale-lizard)  was 
the  largest  reptile 
yet  found  in  Eu- 

m-Iguanodon  Bernessartenm,  restored  by  De  Pauw.  though 


larger  have  been  found  in  the  Jurassic  of  the  United  States.  It  has 
been  classed  among  the  Crocodilians,  but  Prof.  Phillips  has  shown  that 
its  true  position  is  among  the  Dinosaurs.  A  thigh-bone  has  been  found 
sixty-four  inches  long,  27'5  inches  in  circumference  at  the  shaft,  forty- 
six  inches  and  44-25  inches  in  circumference  at  the  two  ends  respect- 
ively (Fig.  696).  According  to  Phillips,  the  animal  was  at  least  fifty 
feet  long,  ten  feet  high  when  standing,  and  of  bulk  proportionate.  It 
was  probably  like  the  Iguanodon  a  vegetable  feeder. 

The  Hylceosaur  was  another  huge  reptile  of  the  same  period,  and 


442 


MESOZOIC  ERA— AGE   OF  REPTILES. 


the  Compsognatlius  a  reptile  of  smaller  size,  but  of  most  extraordinary 
bird-like  character,  viz.,  small  head,  long,  flexible  neck,  large  and  long 


FIG.  694.— Head  of  Megalosaurus.  x  T\j  (restored  by  Phillips). 

hind-leg,  and  small  and  short  fore-leg.     From  its  structure,  it  must 
have  walked  habitually  on  its  hind-legs  alone  (Fig.  697). 

3.  Pterosaurs. — These  flying  reptiles  were  certainly  among  the  most 

extraordinary  animals  that 
have  ever  existed.  The  or- 
der includes  several  genera, 
but  we  will  describe  only 
the  best  known,  viz.,  the 
Pterodactyl  (wing-finger), 
and  the  Khamphorhynchus 
(beak -snout). 

The  Pterodactyl  (Fig. 
698)  combined  the  short, 
compact  body ; 
the  strong  shoul- 
der-girdle, firmly 
united  with  the 
keeled  sternum  ; 


FIG.  695.— Restoration  of  Scelidosaur. 

the  short,  aborted  tail ;  the  long,  flexible  neck,  and  hollow,  air-filled 
limb-bones,  characteristic  of  birds — with  the  head,  and  jaws,  and  teeth, 
of  a  reptile,  and  the  membranous  wings  of  a  bat.  In  the  bat,  however, 
the  membrane  is  supported  by  four  fingers,  enormously  elongated  for 
the  purpose,  and  only  one  finger  is  free  and  clawed  ;  while  in  the  Ptero- 


JURASSIC  ANIMALS. 


443 


dactyl  there  is  only  one  finger,  which  is  enormously  elongated  and 
strengthened  for  the  support  of  the  web,  and  the  others  are  free  and 
clawed. 

The  Rhamphorhynchus  differed  from  the  Pterodactyl  in  having  a 

long  tail ;  and  in  one  species,  R.  phyll- 
urus  (Fig.  700)  (leaf-tail),  this  was  ver- 
tically expanded  at  the  tip  so  as  to  act 
as  a  rudder  in  flying.  In  a  specimen 
from  the  celebrated  Solenhofen  lime- 
stone of  Bavaria,  and  now  in  possession 


FIG.  696.— Femur  of  Ceteosaurus, 
x  &  (after  Phillips). 


Fro.  697.— Compsognathns  (restoration  by  Hux- 
ley). 


of  Prof.  Marsh,  even  the  membranes  of  the  wings  were  perfectly  pre- 
served (Fig.  699).     Fig.  700  is  a  restoration  of  this  species  in  flight. 


FIG.  698.— Pterodactylus  craseiroetris. 


444 


MESOZOIC  ERA— AGE   OF  REPTILES. 


FIG.  699.— Rhamphorhynchus  phyllurus  (after  Marsh). 

The  Pterosaurs  were  of  many  kinds,  which  varied  in  size  from  two 
or  three  feet  to  eighteen  or  twenty  feet  in  alar  extent. 


FIG.  700.— Restoration  of  Rhamphorhynchus  phyllurus  (after  Marsh).    One  seventh  natural  size. 

Birds. — The  class  of  Birds  is  now  so  distinctly  separated  from  all 
others  and  the  connecting  links  obliterated,  that  the  earliest  birds  are 
of  especial  interest  as  throwing  light  on  the  evolution  of  this  class. 
Until  1862  birds  had  been  found  only  in  the  Tertiary,  and  these  were 
already  distinctly  differentiated  as  typical  birds ;  but  in  that  year  there 
was  found  in  the  Solenhofen  limestone,  so  celebrated  for  its  marvelous 
preservations  of  organisms,  a  flying  feathered  Mped,  and  therefore  pre- 
sumably a  bird.  But  how  different  from  our  usual  conceptions  of  this 
class  !  Along  with  its  distinctive  bird  characters  of  feet,  limb-bones, 
beak,  and  especially  of  feathered  wings,  it  had  the  long  tail  (Fig. 
701)  and  toothed  jaws  (Fig.  704)  of  a  reptile.  The  structure  of  the  tail 
is  especially  significant.  In  ordinary  birds  the  tail  proper  is  shortened 
up  to  a  rudiment,  and  ends  in  a  large  bone,  from  which  radiate  the 
feathers  of  the  tail-fan.  In  this  earliest  bird,  on  the  contrary,  the  tail 


JURASSIC  ANIMALS. 


445 


proper  is  as  long  as  all  the  rest  of  the  vertebral  column  put  together, 
consisting,  as  seen  in  the  figure  (Fig.  702),  of  twenty-one  joints,  from 


FIG.  701.— Archaeopteryx  macroura,  restored  (after  Owen). 

which  the  fan-feathers  come  off  in  pairs  on  each  side.  The  tail-fan 
of  this  bird  differs  from  that  of  typical  birds  precisely  as  the  tail-Jin  of 
earliest  fishes  differs  from  that  of  typical  fishes.  The  tail-fan  of  this 
earliest  bird,  like  the  tail-fin  of  earliest  fishes,  was  vertebrated.  This 
wonderful  reptilian  bird  was  called  Archceopteryx  (primordial  winged 
creature),  and  the  species  Macroura  (long- tailed). 

In  1873  another  specimen  of  Archaeopteryx  was  found  in  the  same 
locality,  and  is  now  in  the  Berlin  Museum.  This  Berlin  specimen  has 
been  carefully  examined  by  Vogt,  Marsh,  and  Dames  (Figs.  703  and 
704).  From  examination  of  these  two  specimens  the  following  singu- 


FIG.  702.— A,  Tail  of  Archaeopteryx  macroura;  B,  Vertebrae  enlarged;  C,  a  Feather;  D,  Tail  of  a 
Vulture;  E,  side  view  of  the  same. 


446 


MESOZOIC  ERA— AGE   OF  REPTILES. 


lar  combination  of  bird  and  reptilian  characters  have  been  made  out. 
Among  bird  characters  are  (1.)  The  strong  shoulder-girdle  and  keeled 


FIG.  703.— Archseopteryx  macroura,  Berlin  specimen  (after  Seeley). 

sternum  necessary  for  flying  (but  Pterosaurs  also  have  these).  (2.)  A 
horny  beak  (but  turtles  and  Ehynchosaurs  and  some  Dinosaurs  have 
this).  (3.)  Tridactyl  feet  (some  Dinosaurs  have  these).  (4.)  Feath- 
ered wings  and  tail.  But,  along  with  these,  besides  the  toothed  jaws 
and  long  tail  of  reptiles,  already  mentioned,  there  were  also  the 
following  characters :  1.  The  metatarsals  (three  in  number)  were 
separate,  as  in  reptiles  and  embryo  of  birds.  2.  The  pelvic  bones 
were  unconsolidated,  as  in  reptiles  and  embryo  of  birds.  3.  The  three 
ringers  were  all  free  and  armed  with  claws.  So  complete  is  the  mix- 
ture of  the  two  kinds  of  characters  that  some  zoologists  (Vogt)  be- 
lieve that  the  reptilian  characters  predominate,  and  that  it  should  be 


JURASSIC   ANIMALS. 


447 


called  a  bird-like  reptile.     Most  agree,  however,  that  it  is  a  reptilian 
bird. 

It  is  interesting  to  note  the  different  ways  in  which  the  same  func- 
tion— that  of  flying — is  effected  in  different  animals,  without  violating 


FIG.  704.— Head  of  Archaeopteryx  macroura  (after  Dames). 

the  law  of  limb-structure.  In  the  Bat  the  resisting  plane  is  produced 
by  stretching  a  membrane  between  the  enormously  elongated  palm  and 
finger-bones ;  in  the  Pterodactyl  only  one  finger  is  enormously  en- 
larged and  elongated  for  this  purpose ;  in  the  Bird  the  same  bones  are 


FIG.  705.— 4,  Fore-limb  of  Bat;  B,  Bird;  C,  Archseopteryx;  D,  Pterodactyl. 

shortened  and  consolidated,  and  the  resisting  plane  is  got  by  the  use 
of  feathers.     This  was  the  method  also  in  the  Archaeopteryx,  but  the 


448 


MESOZOIC  ERA— AGE   OF  REPTILES. 


consolidation  was  not  yet  complete.  Fig.  705  represents  wings  of  these 
four  kinds — the  dotted  lines  run  through  corresponding  parts,  and 
show  the  identity  of  structure. 

Origin  of  Birds. — There  can  be  no  doubt,  then,  that  Birds  came 
from  Reptiles.  Further,  it  is  most  probable  that  they  came  from 
Dinosaurs.  It  is  true  that  Dinosaurs  are  the  largest  of  reptiles,  while 
birds,  with  some  exceptions,  are  comparatively  small  animals ;  but  Marsh 
has  shown  that  some  American  Dinosaurs  were  very  small.  The  time 
of  their  origin,  or  separation  from  the  reptilian  stem,  is  still  doubtful, 
but  the  wonderfully  reptilian  character  of  Archseopteryx  shows  that  it 
can  not  be  far  from  the  point  of  origin.  It  was  probably  in  the  Loiver 
Jurassic  or  Upper  Triassic. 

Mammals. — We  have  already  seen  (p.  421)  that  the  first  appearance 
of  this  class  was  in  uppermost  Trias ;  but  as  these  were  few  in  num- 
ber, and  very  near  the  confines  of  Jurassic,  we  regarded  them  as  an- 
ticipations, and  put  off  their  discussion.  In  the  Jurassic  this  anticipa- 
tion was  fully  realized.  In  the  same  formation  (Upper  Jurassic)  in 
which  we  found  the  old  forest-ground  (p.  425)  have  been  found  also 
fourteen  genera  of  small  mammals.  To  this  may  be  added  five  genera 


FIG.  708.  FIG.  709. 

FIGS.  706-710.— JTTKASSIC  MAMMALS:   706.  Amphitherium  Prevostii.     707.  Phascolotherium.     708, 
Amphitherium.    709.  Triconodon.    710.  Plagiaulax. 

from  a  lower  horizon  (Stonefield  states).  If  we  add  to  these  again  four- 
teen genera  (twenty-five  species),  recently  described  by  Marsh,  from  the 
American  Jurassic,  we  have  at  least  thirty- three  Jurassic  genera  known. 
Besides  these,  at  least  five  genera  are  found  in  the  Upper  Trias  of  all 
countries,  and  sixteen  genera  (twenty-four  species),  recently  (1889) 
described  by  Marsh,  from  Upper  Cretaceous  (Laramie).  We  may  say, 
therefore,  that  there  are  now  known  at  least  fifty-four  genera  of  Meso- 
zoic  mammals.  The  number  of  species  is,  of  course,  much  greater. 

Affinities  of  Jurassic  Mammals,— The  Jurassic,  and  indeed  the  Meso- 
zoic  mammals,  as  contrasted  with  mammals  of  later  times,  may  be 
characterized  in  a  general  way  as  small  insectivorous  marsupials,  or, 
perhaps  better,  as  a  type  connecting  insectivores  and  marsupials,  and 
therefore  lower  and  more  generalized  than  either.  They  were,  espe- 


JURASSIC  ANIMALS.  449 

cially  the  earliest  or  Triassic,  decidedly  reptilian  in  some  of  their  char- 
acters.    Of  these  we  mention  only  two. 

1.  Teeth. — A  glance  at  Fig.  711  a,  in  comparison  with  figure  of  The- 
riodont  (Fig.  624  #),  on  page  420,  shows  that  the  teeth  of  some  of  the 


f 

FIG.  711.— A  SERIES  OF  MOLARS  OF  TRIASSIC  AND  JUBASSIC  MAMMALS:  a,  Dromatherium;  b,  Micro- 
nodon;  c,  Amphilestee;  d,  Phascolotherium;  e,  Tnconodon;  /,  Splalacotheriuin  (after  Osborn). 

earliest  mammals  differed  little  from  those  of  Theriodont  reptiles ;  in 
which,  as  already  explained,  the  tuberculation  of  the  molars  character- 
istic of  mammals  had  already  commenced.  In  the  subsequent  course 
of  evolution  the  subordinate  cusps  of  Fig.  711,  «,  #,  c,  d,  e,  were 
shifted  outward  in  the  upper  jaw  and  inward  in  the  lower  jaw,  so  that 
the  cusps  interlocked.  This  forms  the  tritubercular  molar  of  Cope 
(Fig.  711/),  so  common  in  Mesozoic  animals.  From  this  simple  gener- 
alized type  were  afterward  developed  the  more  complex  molars  of  the 
specialized  animals  of  the  Tertiary  and  present  time. 

2.  Reproduction. — There  seems  to  be  no  doubt  that  many  of  these 
animals  were  marsupials,  although  more  generalized  than  any  existing 
marsupials.  Now,  marsupials  in  their  reproduction  approach  reptiles. 
In  typical  mammals  the  embryo  is  attached  to  the  mother  by  a  pla- 
centa, so  that  the  whole  embryonic  development  is  within  the  uterus ; 
in  marsupials,  on  the  contrary,  there  is  no  placental  attachment,  and 
therefore  the  intra-uterine  development  is  very  short  and  imperfect, 
and  is,  in  fact,  completed  outside  the  uterus  in  the  pouch  (mar- 
supium).  In  true  mammals  the  whole  embryonic  development  is 
within  (gestation),  and  the  young  are  born  in  perfect  condition.  They 
are  young-bearers  (viviparous).  In  birds  and  reptiles — egg-bearers 
(oviparous)—  the  whole  of  the  development  takes  place  without  (incu- 
bation). In  marsupials  the  development  is  partly  within  but  mostly 
without.  These,  therefore,  may  be  called  semi-oviparous ',  or  reptilian 
mammals. 

Thus  the  class  of  mammals  has  been  divided  into  two  sub-classes — 
placentals  or  true  mammals,  and  non-placentals  or  reptilian  mam- 
mals. The  latter  includes  the  marsupials,  semi-oviparous,  and  the 
monotr ernes  (Ornithorhynchus,  Echidna,  etc.),  which  are  true  egg-lay- 
ers (oviparous),  like  birds  and  reptiles.  The  non-placentals,  with  the 
exception  of  a  few  opossums  in  America,  are  wholly  confined  now  to 
the  Australian  region.  In  Jurassic  times  they  roamed  in  great  num- 
bers all  over  Europe  and  America. 

Origin  of  Mammals. — In  Theriodonts  and  Theromorphs  we  see 

29 


450  MESOZOIC  ERA— AGE  OF  REPTILES. 

reptiles  reaching  upward  and  forward  toward  mammals.  In  Jurassic 
and  especially  Triassic  mammals  we  see  this  class  reaching  downward 
and  backward  toward  reptiles.  But  the  point  of  union  has  not  yet 
been  found.  The  lowest  and  most  reptilian  of  mammals,  the  egg-lay- 
ing monotremes,  have  not  yet  with  certainty  been  found  fossil;  but 
the  calcined  teeth  recently  found  in  the  embryo  of  the  Ornithorhynchus 
so  strongly  resemble  the  teeth  of  one  family  of  Mesozoic  mammals — 
viz.,  the  Multituberculata  (Fig.  840,  p.  500) — that  it  is  now  believed 
that  these  were,  indeed,  monotremes.  It  is  probable,  therefore,  that 
the  point  of  union  between  the  classes  reptiles  and  mammals  will  be 
found,  not,  indeed,  in  monotremes  proper  (for  these  are  already  special- 
ized), but  in  a  generalized  type  connecting  monotremes  and  marsupials. 
The  time  of  origin  was  probably  the  Lower  Trias  or  Upper  Permian. 
The  earliest  mammals,  such  as  the  Microlestes  and  the  Dromatherium 
from  the  American  Trias,  were  not  far  removed  from  such  a  generalized 
type.  The  order  of  evolution  has  been  expressed  by  Huxley  thus :  1. 
Hypotheria  (below  mammals) ;  2.  Prototheria  (first  or  lowest  mam- 
mals) ;  3.  Metatheria  (transition  mammals) ;  and,  4.  Eutheria  (perfect 
or  true  mammals).  The  first  is  represented  by  the  Theromorphs  of 
Permian  and  Trias,  the  second  by  a  hypothetical  generalized  type  con- 
necting monotremes  and  marsupials  of  the  Triassic,  the  third  by  insec- 
tivorous marsupials  of  the  Jurassic,  and  the  fourth  by  the  true  placen- 
tals  of  the  Tertiary.  Further,  it  is  probable,  as  suggested  by  Osborn,* 
that  "  the  Prototheria  of  Triassic  separated  very  early  into  two  branches 
of  Metatheria — one  more  like  the  marsupial,  the  other  like  insectivora. 
From  the  latter  came  the  Eutheria,  which  again  differentiated  into 
many  specialized  orders. 

Mammals,  then,  existed  in  considerable  numbers  in  the  Jurassic. 
These,  however,  were  not  able  to  contend  with  the  great  Dinosaurs. 
It  was  still  the  age  of  reptiles.  This  class  not  only  predominated,  but 
impressed  their  character  on  all  higher  classes.  The  birds  and  the 
mammals  were  still  reptilian.  From  the  reptilian  stem  the  bird  and 
mammal  branches  were  not  yet  so  completely  separated  that  connect- 
ing links  were  obliterated. 

SECTION  3. — JURA-TKIAS  IN  AMERICA. 

We  have  already  explained  that  these  two  periods  are  not  well  sepa- 
rated in  America.  This  is  partly  on  account  of  the  poverty  of  fossils, 
and  partly  on  account  of  the  continuity  of  conditions  throughout.  It 
seems  best,  therefore,  in  the  present  state  of  knowledge  to  treat  them  to- 
gether as  one  period.  Doubtless  they  will  be  better  separated  hereafter. 

*  Mesozoic  Mammalia,  p.  261,  Transactions  of  the  Academy  of  Sciences,  Philadelphia, 
vol.  ix,  No.  2,  1888. 


JURA-TRIAS   IN  AMERICA.  451 

Distribution  of  Strata.— 1.  Atlantic  Border. — Lying  in  plication- 
hollows,  or  denudation-hollows,  unconformably  on  the  gneiss  (meta- 
morphic  Laurentian  or  Silurian)  of  the  eastern  slope  of  the  Appalachian 
chain,  are  found  very  remarkable  isolated  patches  of  sandstones  or 
sandstones  and  shales,  which  are  referred  to  this  period.  These  patches 
are  strung  along  nearly  parallel  to  the  chain,  and  to  the  coast,  from 
Nova  Scotia  to  the  border  of  South  Carolina.  They  are  represented  on 
the  map  (p.  287)  by  oblique  lines.  One  of  them  is  found  in  Prince 
Edward's  Island,  another  in  Nova  Scotia ;  another  is  the  celebrated 
Connecticut  Eiver  Valley  sandstone ;  a  fourth  commences  in  New  Jer- 
sey, passes  as  a  narrow  strip  through  Pennsylvania,  Maryland,  and  into 
Virginia ;  a  fifth  and  sixth  form  the  Richmond  and  Piedmont  coal- 
fields of  Virginia ;  a  seventh  and  eighth,  the  Dan  River  and  Deep  River 
coal-fields  of  North  Carolina.  As  they  are  isolated,  and  without  con- 
tact with  any  other  formation  unless  unconformably,  their  age  can  not 
be  even  conjectured  from  their  stratigraphical  relations ;  but  the  few 
fossils  which  they  contain  seem  to  refer  them  either  wholly  to  the  Tri- 
assic,  or  else,  more  probably,  partly  to  the  Triassic  and  partly  to  the 
Jurassic. 

In  connection  with  nearly  all  these  patches  are  found  columnar  trap 
or  dolerite  ridges.  These  are  interstratified  with  the  sandstones,  and 
were  partly  outpoured  on  the  sediments  while  these  were  depositing, 
and  partly  forced  subsequently  between  the  strata  (Davis).  Mounts 
Tom  and  Holyoke  are  examples  in  the  Connecticut  Valley,  the  Pali- 
sades of  the  Hudson  in  the  New  Jersey  patch ;  similar  trap-ridges  are 
also  formed  in  all  the  other  patches. 

2.  Plains  and  Rocky  Mountain  Region. — The  geology  of  this  re- 
gion is  still  little  known,  but  there  seems  no  doubt  that  Jura-Trias  is 
widely  distributed  though  largely  concealed  by  subsequent  deposits  of 
Cretaceous  and  Tertiary.     They  are  exposed,  however,  in  narrow  bands 
on  the  flanks  of  the  Black  Hills,  the  Colorado,  Uintah,  and  Wahsatch 
Mountains,  and  over  wider  areas  in  Northwest  Texas,  New  Mexico, 
Arizona,  and  Utah,  where  they  are  called  "  Red  beds."    Their  outcrop 
form  one  of  the  most  conspicuous  erosion-cliffs  (p.  271)  of  the  region 
north  of  Grand  Cafion.     As  may  be  inferred  from  their  almost  univer- 
sal red  color,  they  are  very  barren  of  fossils.     The  same  might  be  in- 
ferred from  the  presence  of  great  beds  of  gypsum  in  the  Plateau  region 
and  beds  of  salt  in  Kansas. 

3.  Basin  Region  and  Pacific  Border. — They  occur  also  over  all  the 
western  part  of  the  Basin  region.     Covered  in  the  valleys  by  recent 
deposits,  but  exposed  on  the  flanks  of  all  the  mountains.     On  both 
sides  of  the  Sierra  and  Cascade  Ranges  they  occur  as  the  auriferous 
slates  of  California  and  northward. 


452 


MESOZOIC  ERA— AGE   OF  REPTILES. 


Life-System. 

The  characterization  of  the  life-system  of  the  Jura-Trias  period 
in  America  is  best  brought  out  in  connection  with  a  description  of 
some  of  the  more  interesting  localities  and  of  their  remarkable  records. 

Connecticut  River  Valley  Sandstone.— The  Strata. — This  locality  has 
been  made  classic  ground  for  the  geologist  by  the  indefatigable  labors 
of  the  late  President  Hitchcock,  of  Amherst.  The  strata  border  the 


Fia.  712.— General  Section  across  Connecticut  River  Sandstone  (after  Davis):  The  black,  trap. 

Connecticut  River,  on  both  sides,  through  the  whole  of  Massachusetts 
and  Connecticut,  as  far  as  Middletown,  where  the  river  trends  to  the 
east  while  the  sandstone  area  passes  straight  on  to  the  sound  at  New 
Haven.  The  whole  forms  an  irregular  area  about  110  miles  long  and 
20  miles  wide.  They  consist  of  red  sandstones  and  shales,  dipping  some- 
what regularly  to  the  east,  at  an  angle  of  about  20°  to  30°,  indicating  a 
thickness  of  at  least  5,000  feet  (Dana)  to  10,000  feet  (Hitchcock).  The 
general  relations  of  the  strata  with  the  intrusive  trap  and  the  under- 
lying gneiss  are  shown  in  the  accompanying  figures  (712  and  713). 
The  trap  is  seen  to  be  conformable  with  the  strata,  but  the  whole  series 
has  been  subsequently  fissured  and  faulted  in  such  wise  that  the  strata 
are  repeated  and  the  thickness  is  apt  to  be  overestimated,  as  already 
explained  on  page  230.  The  trap-ridges  are  formed  by  the  outcrop  of 
the  tilted  and  faulted  sheets  of  lava.  This  regular  dipping  to  the  east 
throughout  the  whole  series  can  be  most  easily  explained  by  supposing 
that  at  the  end  of  the  Jurassic  the  whole  area  of  previously-horizontal 
strata  (Fig.  712,  A)  was  lifted  into  an  incline  of  20°  or  more,  and  after- 
ward cut  away  by  denudation,  as  shown  in  the  diagram  (Fig.  713,  B), 
In  the  elevation  the  strata  were  fissured  and  faulted,  as  shown  in 
Fig.  712. 

- A  a 


FIG.  713. 


The  whole  series  of  sandstone  is  very  distinctly  stratified,  and  in 
many  parts  beautifully  fissile.  When  these  parts  are  broken  open 
along  their  lines  of  lamination,  all  kinds  of  shore-marks  are  found  in 


JURA-TRIAS   IN  AMERICA.  453 

the  greatest  perfection,  viz.,  ripple-marks,  rain-prints,  sun-cracks,  leaf- 
impressions,  and  tracks  of  animals.  It  is  evident,  therefore,  that  this 
was,  throughout,  a  littoral  or  slioal-water  deposit.  But  it  is  at  least 
5,000  feet  thick.  Therefore,  there  must  have  been  subsidence  to  that 
extent.  Here,  then,  we  have  evidence  of  rapid  deposit  (for  the  mate- 
rials are  coarse),  invasion  of  interior  heat  with  aqueo-igneous  fusion, 
subsidence,  formation  oi  fissures,  and  ejection  of  lava. 

These  sandstones  are  poor  in  fossils,  but  the  few  that  are  known  in- 
dicate the  horizon  of  the  Keuper  or  Upper  Triassic  of  Europe.  As 
these  are  found  near  the  middle  of  the  series,  it  is  probable  that  the 
series  represents  the  whole  of  the  Trias  and  part  of  the  Juras  of  Europe. 

The  Record. — The  general  redness  of  the  sandstone  is  sufficient  evi- 
dence that  organic  remains  are  very  scarce ;  and  so,  indeed,  we  find  it. 


FIG.  714.— a,  Frond;  b,  Cone  (after  Hitchcock). 

Two  or  three  fishes,  a  few  leaves,  the  most  perfect  of  which  is  a  species 
of  fern — Clathopteris — and  a  fir-cone  (Fig.  714),  and  a  few  small  frag- 
ments of  thin,  hollow  bones,  which  may  have  belonged  to  either  birds 
or  reptiles,  are  all  that  have  been  yet  found. 

But  by  far  the  most  interesting  portion  of  the  record  in  this  locality 
consists  of  tracks.     These  are  partly  tracks  of  Insects  and  Crustaceans, 


FIG.  716.— Larva  of  an 
Ephemera  (after  II  itch- 
cock). 


FIG.  715.— a,  b,  c,  Tracks  of  Insects,  Crustacea,  or  Worms  (after 
Hitchcock). 


and  partly  of  Reptiles  and,  possibly,  of  Birds.     Some  of  those  which 
have  been  referred  to  Crustaceans  and  Insects  are  shown  in  Fig.  715, 


454  MESOZOIC   ERA— AGE   OF   REPTILES. 

«,  #,  c.  There  has  been  found,  also,  the  whole  form  of  one  insect  appar- 
ently the  larva  of  an  Ephemera  (Fig.  716).  It  is  quite  probable  that 
many  of  the  tracks  were  formed  by  similar  larvee  inhabiting  the  water. 

Reptilian  Tracks. — By  far  the  larger  number  of  tracks  are  those  of 
Reptiles.  More  than  fifty  species  have  been  described  by  Hitchcock.* 
These  vary  extremely,  both  in  size  and  in  character.  In  size,  they  vary 
from  the  track  of  a  living  Triton,  a  half -inch  long,  to  that  of  the  Oto- 
zoum  (Fig.  717),  twenty  inches  long,  and  with  a  stride  of  three  feet. 
Some  had  five  toes,  some  four,  and  some  only  three  functional  toes  on 
the  hind-feet.  Again,  some  had  hind  and  fore  feet  of  nearly  equal  size, 
and  evidently  walked  or  crawled  in  true  quadrupedal  style.  Others  had 
hind-feet  much  larger  than  fore-feet,  and  were  essentially  bipedal  in 
locomotion,  only  putting  down  their  small  fore-feet  occasionally ;  but 
walking  bird-like,  not  hopping  kangaroo-like,  on  their  hind-legs.  In 
connection  with  the  bipedal  tracks  there  have  been  found  what  seemed 
to  be  the  impression  of  a  dragging  tail  (Fig.  718) ;  but  these  are  so 
rare  and  doubtful  that  it  is  generally  believed  the  animals  were  mostly 
long-legged  and  short-tailed. 

The  general  conclusion  from  an  attentive  study  of  these  tracks,  in 
connection  with  the  findings  elsewhere  of  bones  and  teeth,  is  that  they 
are  the  tracks  partly  of  Amphibians  of  the  order  of  LdbyrintJiodonts, 
but  mostly  of  Dinosaurs.  The  hugest  among  them,  the  Otozoum  Moodii 
(Fig.  717),  was  probably  a  long-legged  biped  amphibian,  which  stood 
twelve  feet  high.  The  Anomcepus  (Fig.  719),  a  common  form,  was 
probably  a  Dinosaur,  which  walked  often  on  two  legs  only,  and  in  so 
doing  brought  the  whole  tarsus  and  heel  on  the  ground,  in  the  manner 
of  a  kangaroo  when  resting. 

Supposed  Bird-Tracks.— Those  which  have  been  referred  to  birds 
are  :  1.  Wholly  bipedal,  i.  e.,  there  is  no  evidence  of  fore-feet  at  all.  2. 
They  are  tridactyl.  3.  They  have  a  regular  progression  in  the  number 
of  joints  in  the  tracks,  the  inner  toe  having  two,  the  middle  toe  three, 
and  the  outer  toe  four  joints.  Now,  in  birds,  the  inner  toe  has  three, 
the  middle  toe  four,  and  the  outer  toe  five  joints,  but  the  last  two  joints 
in  each  case  make  but  one  division  of  the  track,  so  that  the  track  is  ex- 
actly what  is  given  above.  The  discovery,  however,  that  Dinosaurs 
have  but  three  functional  toes  on  the  hind-foot,  and  that  they  also  have 
the  same  number  of  joints  as  birds,  has  greatly  shaken  confidence  in  the 
ornithic  character  of  these  tracks.  Only  the  absence  of  fore-feet  tracks, 
therefore,  remains.  But  as  many  of  these  early  reptiles  walked  occa- 
sionally on  two  legs,  it  is  not  impossible  that  some  of  them  always 
walked  thus.  It  is  quite  possible  or  even  probable,  therefore,  that  all 
these  tracks  are  those  of  Reptiles.  Assuming  them  to  be  those  of 

*  About  seventy  species  are  now  known  (E.  H.  Hitchcock). 


JURA-TRIAS  IX  AMERICA. 


455 


Birds,  they  vary  in  size  from  those  of  a  snipe  to  those  of  the  great 
Brontozoum,  eighteen  inches  long,  and  with  a  stride  of  four  feet  (Fig. 

720).  This  huge  bird,  if  bird  it  was, 
must  have  been  at  least  fourteen  feet 
high  (Dana).  Such  a  huge  animal  must 
have  been  wingless,  like  the  ostrich,  etc., 


FIG.  717. 


FIG.  718. 


FIG.  719. 


FIGS.  717-719.— KEPTILE-T RACKS  (after  Hitchcock):  717.  Otozoum  Moodii:  a,  hind-foot,  x 
fore-foot,  x  ^j.  718.  Gigautitherium  caudatum,  x  ^j.  719.  Anomoepue  minor,  x  J:  a, 
foot;  b,  fore-foot. 


for  its  size  is  far  beyond  the  limit  with- 
in which  flight  is  possible. 

We  have  expressed  a  doubt  as  to 
whether  these  tracks  be  those  of  birds 
or  reptiles.  This  is  not  so  strange  as 
it  may  at  first  appear.  These  two  class- 
es are,  indeed,  now  very  widely  sepa- 
rated, but  then  they  were  very  closely 
allied.  There  were  probably  animals 
then  living  which,  even  if  we  saw  them, 
might  puzzle  us  to  decide  whether  to 
call  them  reptilian  birds  or  bird-like 
reptiles.  These  two  classes  were  not  yet 
fairly  disentangled  and  separated  from 
each  other. 

We  may  easily  imagine  the  circum- 
stances under  which  these  tracks  were 
formed.  During  the  Jura-Trias  period 


FIG.  720.— Track  of  Brontozonm  gigan- 
teum,  x  £  (after  Hitchcock). 


456 


MESOZOIC  ERA— AGE   OF  REPTILES. 


there  was  in  the  region  of  the  Connecticut  Valley  a  shallow  inland  sea, 
connected  by  a  narrow  outlet  with  the  ocean.  Into  this  the  tides 

flowed  and  again 
ebbed,  leaving  exten- 
sive flats  of  mud  or 
sand  ribbed  with  rip- 
ple-marks. A  pass- 
ing shower  pitted  the 
soft  mud,  and  the 
sun,  coming  out 
again  from  the 
breaking  clouds, 
dried  and  cracked 
it.  Huge  bird-like 
reptiles,  and  possibly 
reptilian  birds,  saun- 
tered near  the  shore- 
margin  in  search  of 
The  tide  came 
again  with  its 

freight  of  fine  sediments,  gently  covered  the  tracks,  and  preserved  them 
forever.  This  occurred  constantly  for  many  ages  about  the  end  of  the 
Triassic  or  the  beginning  of  the  Jurassic  period,  for  the  tracks  are 
found  near  the  middle  of  the  series  of  strata. 

Richmond  and  North  Carolina  Coal-Fields. — The  patches  occurring 
in  Virginia  and  North  Carolina  are  coal-bearing.  They  constitute  the 
Eichmond  and  Piedmont  coal-fields  of  Virginia,  and  the  Deep  Eiver 
and  Dan  Eiver  coal-fields  of  North  Carolina.  Fig.  722  gives  a  general- 


FIG.  721.— Portion  of  a  Slab  with  Tracks  of  several  Species  of  Bronto- 
zoum  (after  Hitchcock). 


in 


FIG.  722.— Section  across  Richmond  Coal-field  (after  Daddow). 

ized  section  of  the  Eichmond  coal-fields  taken  from  Daddow.  The 
strata  of  this  field  are  sandstone  and  shales,  700  to  800  feet  thick,  lying 
in  irregular  erosion-hollows  of  the  gneiss.  All  the  phenomena  of  a 
coal-field  are  here  repeated,  viz.,  interstratified  seams  of  coal  and  bfcds 
of  iron-ore,  under-day  s  with  roots,  and  roof -shales  with  leaf -impressions. 
There  are  several  seams  of  coal,  the  lowest  of  which  is  almost  in  con- 
tact with  the  gneiss.  Some  of  the  seams  are  of  great  thickness — 
thirty  to  forty  feet — and  the  coal  is  very  pure.  It  is  probable  that  this 
'  coal,  like  that  of  the  Carboniferous  times,  was  formed  in  a  marsh, 
which  was  sometimes  converted  into  a  lake.  The  plants  found  are 
very  decidedly  Upper  Triassic  and  Lower  Jurassic,  viz.,  Cycads,  Coni- 


JURA-TRIAS  IX   AMERICA. 


457 


fers,  Equisetae,  and  Ferns.  Fontaine  makes  them  Rhcetic,  i.  e.,  transi- 
tive between  Triassic  and  Jurassic.  The  animals  indicate  the  same 
horizon. 


FIG.  723.— Dictyopyge  macrura,  a  Ganoid  (.after  Emmons). 

The  Deep  River  and  Dan  River  coal-fields  of  North  Carolina  are 
very  similar  to  those  in  Eastern  Virginia,  except  that  in  the  Deep  River 
coal-fields  the  coal-bearing  portion,  which  seems  to  correspond  with 
the  whole  of  the  Richmond  strata,  is  underlaid  by  3,000  feet  of  barren 
sandstone.  If  we  call  the  coal-measures  Upper  Trias  or  Lower  Juras, 
these  barren  sandstones  are  certainly  Triassic.  In  their  upper  portion, 
and  therefore  probably  in  the  Upper  Triassic,  Emmons  found  jaws  of 
a  Marsupial,  which  he  names  Dromatherium  sylvestre  (Fig.  729).  As 
this  is  one  of  the  earliest,  so  is  it  also  one  of  the  most  reptilian  of  mam- 
mals. According  to  Osborn,  it  had  many  reptilian  characters  of  teeth, 
e.  g.,  conical  premolars  and  imperfectly  divided  fangs,  and  imperfect 
cusps  in  the  molars  (Fig.  711,  a)  as  in  the  Theromorph  reptiles.  Until 
the  recent  discoveries  of  Marsh,  this,  and  perhaps  another  genus  from 
the  same  place,  was  the  only  mammal  known  from  the  Jura-Trias  of 
America.  We  give  in  Figs.  723-729  some  of  the  plants  and  animals  of 


FIG.  724. 


FIG.  725. 


FIGS.  724,  725.— FOSSILS  OF  NORTH  CAROLINA  AND  RICHMOND  COAL-BASINS  (after  Emmons):  724. 
Walchia  diffusus.    725.  Podozamites  Emmonsi. 


458 


MESOZOIC  ERA— AGE  OF  REPTILES. 


FIG.  728. 


FIG.  729. 


FIGS.  726-729.— FOSSILS  OF  NORTH  CAROLINA  AND  RICHMOND  COAL-BASINS  (after  Emmons):  726. 
Neuropteris  linsefolia— Richmond  Coal.  727.  Pecopteris  falcatus.  728.  Neuropteris.  729.  Jaw 
of  Dromatherium  sylvestre. 

these  two  basins.  Tridactyl  tracks  like  those  in  Connecticut  have  also 
been  found  in  New  Jersey  and  in  Pennsylvania. 

Other  Patches. — In  other  patches,  especially  in  New  Jersey,  Penn- 
sylvania, and  Nova  Scotia,  reptilian  bones  and  teeth  have  been  found, 
representing  Dinosaurs  and  Crocodilians  or  Lacertians. 

Interior  Plains  and  Pacific  Slope. — The  Jura-Trias  of  the  interior 
plains  are  singularly  deficient  in  fossils.  The  gypsum  in  many  of  them 
furnishes  the  explanation.  They  were  probably  formed  in  interior  and 


Fia.  730. 


FIG.  731. 


FIGS.  730,  731.— JURASSIC  FOSSILS  OF  UTAH  (after  Meek):  730.  Belemnites  densus.    731.  Gryphaea 

calceola. 

very  salt  seas,  which  are  usually  deficient  in  life.  The  two  periods  are, 
however,  in  some  places  at  least,  better  separated  than  on  the  Atlantic 
slope,  probably  because  of  more  variable  conditions. 


JURA-TRIAS   IN  AMERICA. 


459 


On  the  slopes  of  the  Black  Hills  and  on  the  South  Platte  undoubted 
Jurassic  fossils  occur,  indicating  an  open  sea.  In  New  Mexico  New- 
berry  found  impressions  of  plants,  indicating  the  same  horizon  as  in 


FIG.  735.  FIG.  736.  FIG.  737.  FIG.  739. 

FIGS.  732-739.— PLANTS  OF  THE  JURA-TRIAS  (after  Newberry):  732.  Branch  of  Conifer  (Brachyphyl- 
Jum).  733.  Branch  of  Conifer.  734.  Conifer,  Branch  and  Fruit.  735.  Zamites  occidentalis. 
736.  Otozamites  Macombii.  737.  Podozamites  crassifolia.  738.  Taeniopteris  elegans.  739. 
Alethopteris  Whitneyi. 


460 


MESOZOIC  ERA— AGE   OF   REPTILES. 


North  Carolina  and  Virginia — i.  e.,  Upper  Triassic.     Some  of  these 

are  given  (Figs.  732-739). 

On  the  Pacific  coast  marine  life  no  doubt  abounded,  as  this  was 

the   margin  of   an   open   sea;   but  the   rocks  here   are  very  highly 

metamorphic,  and 
the  fossils,  there- 
fore, mostly  de- 
stroyed. Wherever 
this  is  not  the  case, 
the  rocks  abound 
in  fossils.  InHum- 
boldt  County,  Ne- 
vada, for  example, 
the  strata  in  some 
places  seem  almost 


FIG.  740. 


FIG.  741. 


FIG.  742. 


FIGS.  740-742.—  CALIFORNIA  JURA-TRTAS  SHELLS:  740.  Gryphasa  spe-    wholly  made  up  of 
ciosa  (after  Gabb).     741.  Tris;onia  pandicosta  (after  Gabb).     742. 


Ceratites  Whitney!  (after  Gabb). 

(Fig.  742).     In  the 

same  locality  the  remains  of  an  Enaliosaur  (sea-saurian)  have  been 
found.  On  account  of  the  marine  conditions  prevalent,  the  two  peri- 
ods are  easily  separable  on  the  Pacific  coast. 

Recent  Discoveries.  —  Very  recently  in  Colorado  and  Wyoming,  in 
beds  which  are  referred  to  the  Uppermost  Jurassic,  a  large  number  of 
most  extraordinary  reptiles  have  been  found  and  described  by  Marsh 
and  Cope.  Also,  in  the  Wyoming  beds,  Marsh  has  discovered  some 
twenty-five  species  of  Marsupial  mammals  and  a  reptilian  bird  (Lao- 
pteryx).  The  beds  from  which  all  these  have  been  taken  are  called, 
from  their  most  abundant  and  characteristic  form,  the 
Atlantosaur  beds.  These  discoveries  are  treated  sepa- 
rately, not  only  on  account  of  their  great  importance, 
but  also  and  especially  because  they  belong  to  an  en- 
tirely different  horizon,  viz.,  the  uppermost  Jurassic, 
passing  into  the  Cretaceous.* 

Dinosaurs.  —  The  most  abundant  and  the  largest 
reptiles  found  here  are  Dinosaurs.  Some  ten  or  twelve 
species  of  this  order  have  been  described  by  Cope,  and 
fifteen  or  twenty  species  by  Marsh.  Some  of  these  are 
from  the  east  slope  of  the  Colorado  Mountains,  but 
the  most  important  have  been  found  on  the  west  slope. 


FIG.  743.— Dorsal  ver- 
tebra of  Coelurus 
fragilis,  trans- 
.  verse  section  (af- 
ter Marsh). 


*  The  Atlantosaur  beds  are  classed  with  the  Jurassic,  because  of  the  great  gap  between 
it  and  the  Dakota  Cretaceous.  But  since  this  gap  has  been  filled  (see  p.  478),  the  ques- 
tion again  returns  whether  they  should  be  called  Uppermost  Jurassic  or  Lowermost  Cre- 
taceous. They  apparently  corresponds  to  the  Wealden,  which  many  geologists  class  with 
the  Cretaceous.  Marsh,  however,  regards  them  as  decidedly  Jurassic. 


JURA-TRIAS  IX   AMERICA. 


461 


In  the  museum  of  Yale  College  there  are  now  the  remains  of  several 
hundred  individuals.     These  American  Jurassic  Dinosaurs  were  prob- 


FIG.  744.— 1.  Bones  of  left  fore-leg  of  Morosaurus  grandis  (after  Marsh).  One  twentieth  natural 
size,  s,  scapula;  c,  coracoid;  h,  humerus;  r,  radius:  u,  ulna;  uc,  ulnar  carpal;  1,  first  meta- 
carpal;  Vmc,  fifth  metacarpal.  3.  Bones  of  left  hind-leg  of  Morosaurus  grandis.  One  twentieth 
natural  size.  il.  ilium;  is,  ischium;  p,  pnbis;  /,  femur;  t,  tibia;  f.  fibula:  a,  astragalus;  c,  cal- 
caneum;  Vmt,  fifth  metatarsal. 

ably  the  largest  land  animals  that  have  ever  lived.  Cope  describes 
one  (Camarasaurus)  with  a  thigh-bone  six  feet  long.  Marsh  describes 
one  (Atlantosaurus  immanis)  with  thigh-bone  about  eight  feet  long. 


462 


MESOZOIC  ERA— AGE  OF  REPTILES. 


Along  with   these  huge  animals  lived  also  the  smallest  Dinosaurs  yet 
known — one  of  them,  Nanosaurus  agilis,  being  about  the  size  of  a  cat. 


FIG.  745.— Pelvic  arch  of  Morosaurus  grandis  (after  Marsh),  seen  from  in  front.  One  sixteenth 
natural  size:  a,  first  sacral  vertebra;  b,  transverse  process  of  first  sacral  vertebra;  c,  trans- 
verse process  of  second  vertebra;  p,  fourth  or  last  sacrai  vertebra;  nc,  neural  canal;  il,  ilium; 
is,  ischium;  pb,  pubis. 

The  characteristics  of  these  ancient  reptiles  have  been  worked  out 
with  great  skill  by  Marsh,  according  to  whom  the  vertebrae  of  many  of 
them  were  full  of  large  cavities,  so  as  to  make  these  enormous  bones 
as  light  as  possible.  This  character  reached  its  highest  expression  in 
Cceluria  of  Marsh  (Fig.  743). 

The  American  Dinosaurs  were  not  only  remarkable  for  size  and 
number  but  also  for  their  great  variety  of  forms.  According  to  Marsh, 
some  of  them  were  reptile-footed  (Sauropodd),  some  beast-footed 


FIG.  746.— Brontosaurus  excelsis,  x  ^  (restored  by  Marsh). 

(TJieropodd],  some  bird-footed  (Ornitliopoda),  and  some  belonged  to  a 
most  remarkable  family,  Stegosauria  (plate-covered  Saurians),  not  pre- 
viously recognized. 


JURA-TRIAS   IN   AMERICA. 


463 


The  Sauropoda  were  the  hugest  of  all.     They  were  five-toed,  planti- 
grade, and  quadrupedal.     Their  large,  hollow  limb-bones  (Fig.  744) 


FIG.  747.— 1.  Tooth  of  Laosaurus  altus  (after  Marsh),  front  view.  2.  The  same,  side  view.  Both 
twice  natural  size.  3.  Bones  of  the  left  hind-leg  of  Laosaurus  altus  (after  Marsh).  One  eighth 
natural  size:  il,  ilium;  «,  ischium;  p,  pubis;  p',  post-pubic  bone;  f,  femur;  t,  tibia;/',  fibula; 
a,  astragalus;  c,  calcaneum;  /,  first  metatarsal;  iVmt,  fourth  metatarsal. 

and  massive  pelvis  (Fig.  745)  show  that  they  walked  with  the  body  well 
lifted  from  the  ground  (Fig.  746).  They  were  probably  herbivorous. 
Good  examples  of  these  are  seen  in  the  Atlantosaurus  (a  thigh  of  which 
was  found  more  than  eight  feet  long  and  twenty-five  inches  thick,  the 
animal  itself  being  probably  at  least  one  hundred  feet  long) ;  the 
Brontosaurus,  sixty  feet  long  (Fig.  746) ;  and  the  Morosaurus  (Fig. 
744,  745). 


464 


MESOZOIC   ERA— AGE   OF  REPTILES. 


The  TUeropoda  included,  among  foreign  representatives,  the  Me- 
galosaur  and  Scelidosaur,  already  figured  (p.  442),  and  also  several 

2 


PIG.  748.— 


.  748.— 1.  Bones  of  left  fore-leg  of  Camptosanms  dfcpar  (after  Marsh):  g,  scapula;  e.  coracoid;  A, 
humerus;  r,  radius;  u.  ulna;  /,  first  digit;  V.  fifth  digit.    2.  Bones  of  left  hind-leg  of  Campto- 
notns  dispar:   U,  ilium;  ig,  iechium;  p,  pnbis;  p',  post-pubis; /,  femur: ;  /,  tibia;  /,  fibula;  a, 
tragalus;  c,  calcaneum;  /,  first  metatarsal;  IVmt,  fourth  metatarsal.    Both  figures  one-twelfth 


natural  size. 


American  genera.  They  were  four-  to  five-toed,  digit  igrade,  and.  bipe- 
dal This  is  shown  by  the  disparity  in  size  of  hind  and  fore  limbs. 
They  were  carnivorous. 

The  Ornithopoda  included,  among  foreign  representatives,  the  Igu- 
anodon  and  Compsognathus,  already  figured  (pp.  441  and  443),  together 


JURA-TRIAS  IN  AMERICA. 


465 


with  many  American  genera,  such  as  Laosaurus  (Fig.  747)  and  Camp- 
tosaurus  (Fig.  748).  They  were  three-toed,  digitigrade,  bipedal  herbi- 
vores. 

The  Stegosaurs  were  perhaps  the  most  remarkable  of  all.      They 

2 


c 


FIG.  749. 

PIG.  749.— 1.  Bones  of  left  fore- leg  of  Stegosaurus  ungulatus  (after  Marsh):  «,  scapnla;  c,  coracoid; 
h,  humerus;  r,  radius;  y,  ulna;  7,  first  digit;  F,  fifth  digit.  2.  Bones  of  left  hind-leg  of  Stego- 
saurns ungulatus:  il,  ilium;  is,  ischium;  p,  pubif;  »',  poet-pubie;  f,  femur;  t,  tibia;/',  fibula; 
a,  astragalus;  c,  calcaneum;  /,  first  digit;  V,  fifth  digit.  One  sixteenth  natural  size. 

FIG.  750. — Outlines  representing  transverse  sections  through  brain  of  Stegosaurus  ungulatus,  and 
sacral  cavity  :  6,  brain;  «,  sacral  cavity.  One  fourth  natural  size  (after  Marsh). 

30 


466 


MESOZOIC  ERA— AGE   OF  REPTILES. 


were  well  protected  with  broad  plates,  some  of  which  have  been  found 
three  feet  in  diameter,  and  armed  with  sharp  spines  two  feet  long. 
These  latter  were  placed  on  each  side  of  the  powerful  tail,  near  the 


jf 
pf 


Fig.  751.— Stegosaurus  sterrops,  x  i  (after  March). 

end,  and  must  have  been  very  formidable  weapons  of  offense.  The  dis- 
parity in  size  of  hind  and  fore  limbs  (Fig.  749),  greater  than  in  any 
known  Dinosaur,  shows  that  they  walked  habitually  on  the  hind-legs, 
like  the  Ornitliopoda.  Like  them,  also,  they  probably  had  three  to 

four   toes    on   the 

*  A<^fev  hind  -  feet.       The 

brains  of  all  Juras- 
sic Dinosaurs  were 
very  small  in  com- 
parison with  living 
reptiles,  but  this 
was  especially  true 
of  Stegosaurs.  To 
make  up  for  this 
;7'7fibuiar>;fir8t  digit;  F,  fifth  digit,  deficiency  they  had 

an  enormous  enlargement  of  the  spinal  cord  in  the  sacral  region.  This 
sacral  brain— if  we  may  so  call  it — was  ten  times  bigger  than  the  cran- 
ial brain  (Fig.  750).  It  was  necessary  in  order  to  work  the  powerful 
hind-legs  and  tail. 

Ichthyosaurs.— Besides  the  Dinosaurs,  Marsh  describes  from  the 
same  formation  (Jurassic),  but  from  a  lower  horizon,  an  Ichthyosau- 
rian,  but  differing  entirely  from  the  Ichthyosaurus  of  the  European 
Jurassic  in  being  toothless.  On  this  account  he  calls  the  genus  Bap- 
tanodon.  This  reptile  had  six  digits  in  both  fore  and  hind  feet— a 
new  and  most  remarkable  feature  (Fig.  752). 

Birds.— In  1881  Marsh  discovered  in  the  same  beds,  the  Atlanto- 
saur  beds  of  Wyoming,  a  Jurassic  bird  (Laopteryx),  the  only  one  yet 
known  in  America.  It  was  undoubtedly  a  reptilian  bird,  probably  with 


FIG.  752.— Left  hind  paddle  of  Baptanodon  discus  (after  Marsh),  seen 
from  below.    One  eighth  natural  size:  f  femur;  t,  tibia;  i,  interme- 


JURA-TRIAS  IN  AMERICA. 


467 


teeth  and  U-concave  vertebra, ;  but  the  remains  are  too  imperfect  to 
permit  distinct  characterization. 

Mammals. — Lastly,  in  the  same  beds,  Marsh  has  discovered  some 
.twenty-five  species  of  small  marsupial  mammals.  According  to  him, 
these  early  mammals  were  not  typical  Marsupials,  but  a  generalized 
type  connecting  that  order  with  Insectivora.  He  makes  of  them  two 
sub-orders,  Pantotheria  and  Allotheria.  Figs.  753  and  754  are  repre- 
sentatives of  these  two  types. 

Physical  Geography  of  the  American  Continent  during  the  Jura- 
Trias  Period. — During  Palaeozoic  times  the  Atlantic  shore-line  was 
certainly  farther  east  than  it  was  subsequently,  probably  farther  east 
than  it  is  now  (p.  288).  At  the  end  of  the  Palaeozoic  occurred  the  Ap- 
palachian revolution.  Coincidently  with  the  up-pushing  of  the  Appa- 
lachian chain,  the  sea-border  probably  went  downward,  and  the  shore- 


FIG.  753.— Right  lower  jaw  of  Diplocynodon  victor  (after  Marsh),  outside  view.    Twice  natural  size: 
a,  canine;  b,  condyJe;  c,  coronoid  process;  d,  angle. 

line  advanced  westward  on  the  land.  During  the  Jura-Trias  the 
shore-line  to  the  north  was  still  beyond  what  it  is  now,  for  no  Atlantic 
border  deposit  is  visible ;  and  along  the  Middle  and  Southern  States 


FIG.  754.— Left  lower  jaw  of  Ctenacodon  eerratus  (after  Marsh),  inner  view.  Four  times  natural  size. 

it  was  certainly  beyond  the  bounding-line  of  Tertiary  and  Cretaceous 
(see  map,  p.  291),  for  all  the  Atlantic  deposits  of  this  age  have  been 
covered  by  subsequent  strata ;  and  yet  probably  not  much  beyond,  for 
some  of  these  Jura-Trias  patches  seem  to  have  been  in  tidal  connection 
with  the  Atlantic  Ocean.  It  is  probable,  therefore,  that  the  shore-line 
was  a  little  beyond  the  present  New  England  shore-line,  and  a  little 


468  MESOZOIC  ERA— AGE   OF  REPTILES. 

beyond  the  old  Tertiary  shore-line  of  the  Middle  and  Southern  Atlan- 
tic States. 

A  little  back  from  this  shore-line,  and  at  the  foot  of  the  then  Ap- 
palachian chain,  there  was  a  series  of  old  erosion  or  plication  hollows 
stretching  parallel  to  the  chain.  The  northern  ones  had  been  brought 
down  to  the  sea-level,  and  the  tides  regularly  ebbed  and  flowed  there 
then  as  in  the  bay  of  San  Francisco,  or  Puget  Sound,  at  the  present 
time.  In  the  waters  of  these  bays  lived  swimming  Reptiles,  Croco- 
dilian and  Lacertian,  and  on  their  flat,  muddy  shores  walked  great 
bird-like  Reptiles,  and  possibly  reptilian  Birds.  The  more  southern 
hollows  seemed  to  have  been  above  the  sea-level,  and  were  alternately 
coal-marsh  and  fresh-water  lake,  emptying  by  streams  into  the  At- 
lantic. Since  that  time  the  coast  has  risen  200  or  300  feet,  and  these 
patches  are  therefore  elevated  so  much  above  the  sea- level. 

Meanwhile,  somewhat  similar  changes  were  going  on  in  the  western 
portion  of  the  continent.  During  Palaeozoic  times,  the  Pacific  shore- 
line was  just  east  of  the  Sierra  Range,  and  the  place  of  this  range  was 
a  marginal  sea-bottom.  At  the  end  of  the  Palaeozoic,  coincidently  with 
Appalachian  revolution  already  explained  (p.  409),  the  Utah  Basin 
region  was  elevated  and  became  land,  while  the  Nevada  Basin  region 
subsided,  and  the  Pacific  shore-line  advanced  eastward  to  Battle  Mount- 
ain. But  the  whole  area  between  this  Basin  region  continent  and  the 
Palaeozoic  area  of  eastern  North  America,  including  the  Plateau  region 
and  the  Plains  region,  was  covered  by  one  or  more  shallow  inland  seas, 
with  imperfect  connection,  or  none  at  all,  with  the  ocean,  and  in  which, 
therefore,  gypsum  and  salt  deposited  by  evaporation.  At  least  once  dur- 
ing Jurassic  times  this  inland  sea  became  broadly  connected  with  the 
ocean,  so  that  oceanic  conditions  prevailed.  The  place  now  occupied 
by  the  Wahsatch  Mountains  was  then  a  marginal  sea-bottom,  bordering 
the  Basin  region  continent.  On  the  west  the  Pacific  shore-line  was 
some  distance  east  of  the  Sierra,  and  the  place  of  that  range  was  still  a 
sea-bottom,  though  not  so  closely  marginal  as  in  Palaeozoic  times. 

Disturbances  which  closed  the  Period. — This  long  Jura-Trias  period 
was  closed,  and  the  Cretaceous  period  inaugurated,  by  the  Sierra  revo- 
lution, by  which  the  sediments  accumulated  along  the  then  Pacific 
shore-bottom,  yielding  to  the  lateral  pressure,  were  mashed  together 
and  swollen  up  into  the  Sierra  and  Cascade  Ranges,  and  the  coast-line 
transferred  westward  to  the  other  side  of  these  ranges.  Coincidently 
with  this  change  probably  occurred  on  the  Atlantic  slope  the  elevation 
of  the  Jura-Trias  sounds  and  the  outbursts  of  igneous  matter,  forming 
the  trap-ridges  already  spoken  of  (pp.  451  and  452).  Extensive  changes 
also  occur  at  the  same  time  over  the  whole  region  of  the  inland  seas,  by 
subsidence  and  the  inauguration  of  oceanic  conditions,  which  continued 
to  prevail  during  the  Cretaceous.  There  is  reason  to  believe  also  that 


CKETACEOUS   PERIOD.  469 

many  of  the  Basin  ranges  were  formed  at  this  time  (King),  although 
their  present  forms  were  given  much  later  (p.  265),  It  was  essentially 
a  period  of  mountain-making  in  the  western  part  of  the  American 
Continent. 

SECTION  4. — CRETACEOUS  PERIOD. 

The  most  general  characteristic  of  this  period  is  its  transitional 
character.  In  it  Mesozoic  types  are  passing  out,  and  Cenozoic  or 
modern  types  are  coming  in,  and  the  two  types  therefore  coexist  side 
by  side.  Nearly  everywhere  in  America,  as  far  as  known,  the  Creta- 
ceous lie  unconformably  on  the  Jurassic  or  still  lower  rocks. 

Rock-System — Area  in  America. — 1.  On  the  Atlantic  border  going 
southward,  we  find  no  Cretaceous  rocks  until  we  reach  New  Jersey. 
Here  we  find  a  small  patch  peeping  out  from  under  the  edge  of  the 
overlying  Tertiary,  and  marked  on  the  map  (p.  291)  by  oblique  inter- 
rupted lines.  This  patch  passes  through  New  Jersey,  Delaware,  Mary- 
land, to  the  borders  of  Virginia.  Passing  south,  we  find  no  continuous 
area  until  we  reach  Georgia ;  yet  it  underlies  the  Tertiary  in  all  this 
region,  as  is  shown  by  the  fact  that  the  rivers  in  North  and  South 
Carolina  cut  through  the  Tertiary  and  expose  the  Cretaceous  in  many 
places.  2.  The  Gulf-border  Cretaceous  commences  in  Western  Middle 
Georgia,  covers  all  the  prairie  region  of  Middle  Alabama,  the  northeast- 
ern or  prairie  region  of  Mississippi,  then  runs  northward  as  a  narrow 
strip  through  Tennessee  nearly  to  the  mouth  of  the  Ohio.  It  then  dis- 
appears beneath  the  Tertiary,  to  reappear  as  an  area  bordering  the  Gulf 
Tertiary  on  the  west  side.  3.  On  the  interior  plains,  the  Cretaceous 
connecting  with  the  Gulf-border  area  stretches  northwestward  to  arctic 
regions,  occupying  nearly  the  whole  of  the  great,  grassy,  level  Western 
Plains  called  Prairies — though  much  of  it  is  overlaid  by  the  subsequent 
Tertiary.  4.  In  the  Rocky  Mountain  region  Cretaceous  strata  occupy 
all  the  Plateau  region*— i.  e.,  the  region  between  the  Eastern  range  and 
the  Wahsatch  range,  except  where  overlaid  by  Tertiary  or  removed  by 
erosion.  Eecent  investigations  in  Mexico  *  render  it  probable  that  this 
area  stretches  also  westward  through  Northern  Mexico  to  the  Pacific. 
.  5.  On  the  Pacific  border,  Cretaceous  strata  form  a  large  part  of  the  Coast 
Ranges,  and  also  in  places  the  lowest  western  foot-hills  of  the  Sierra 
Range.  Whitney  has  estimated  the  thickness  of  the  Cretaceous  rocks 
in  portions  of  the  Coast  Range  as  20,000  feet,  and  Dillon,  30,000  feet. 

Physical  Geography  in  America,— It  is  not  difficult  from  the  Creta- 
ceous area  just  given  to  reconstruct  approximately  the  physical  geog- 
raphy. At  that  time  the  Atlantic  shore-line  in  all  the  northern  portion 
of  the  continent  was  farther  out  or  east  than  now,  for  the  Cretaceous 

*  American  Journal  of  Science,  vol.  x,  p.  386,  1875. 


470  MESOZOIC  ERA— AGE   OF  REPTILES. 

of  this  part  is  all  now  covered  by  sea.  From  New  Jersey  southward 
the  shore-line  was  then  farther  in  or  west  than  now.  From  Maryland 
to  Georgia  the  shore-line,  though  farther  in  than  now,  was  farther  out 
than  during  the  Tertiary,  as  the  Cretaceous  is  covered  by  the  later  de- 
posits. The  Gulf  was  much  more  extended  both  northward  and  west- 
ward than  either  now  or  in  Tertiary  times,  its  shore-line  being  along 
the  extreme  limit  of  the  Cretaceous  of  this  region.  From  the  Gulf 
there  extended  northwestward  an  immensely  wide  sea,  covering  the 
Plains  region  and  the  Eocky  Mountain  region  as  far  westward  as  the 
Wahsatch  Eange,  and  dividing  the  continent  into  two  continents,  an 
eastern  or  Appalachian,  and  a  western  or  Basin  region  continent.  The 
place  of  the  Wahsatch  range  was  then  the  marginal  bottom  of  this  in- 
terior Cretaceous  sea.  The  Pacific  Ocean  at  that  time  washed  against 
the  foot-hills  of  the  Sierra  Eange,  the  place  of  the  Coast  Eange  being 
thus  its  marginal  bottom.  These  facts  are  represented  in  the  accom- 
panying map.  The  probable  connection  of  the  Gulf  with  the  Pacific 
is  also  indicated. 


FIG.  755.— Map  of  North  America  irf  Cretaceous  Times. 

Rocks. — The  rocks  of  the  Cretaceous  period  consist  of  sands,  and 
clays,  and  limestones,  as  in  other  periods,  but,  as  a  whole,  are  less  fre- 
quently metamorphic  than  in  the  older  rocks.  There  is,  however,  one 
kind  of  rock  found  in  this  age  in  Europe  which  is  so  peculiar  and  so 
interesting  that  it  must  not  be  passed  over  in  silence.  We  refer  to  the 
white  chalk  of  England  and  France,  from  which  the  formation  and  the 
period  take  their  name,  "  Cretaceous" 

Chalk. — Chalk  is  a  soft,  white,  pure  carbonate  of  lime.     Scattered 


CRETACEOUS  PERIOD. 


471 


through  the  soft  mass  are  found  very  characteristic  nodules  of  pure 
flint.  These  nodules  are  of  various  sizes  and  shapes,  sometimes 
scattered  irregularly, 
sometimes  arranged  in 
layers.  Often  some 
fossil,  especially  a 
sponge,  forms  the  nu- 
cleus around  which 
the  aggregation  of  the 
siliceous  matter  takes 
place.  On  account  of 
its  extreme  softness, 
chalk  is  often  sculpt- 
ured by  erosive  agen- 
cies into  fantastic  cliffs 
and  needles  (Fig.  756). 

Examined  with  the  microscope,  chalk  is  found  to  be  composed  largely 
of  Rhizopod  shells,  and  of  Coccoliths  and  Coccospheres  (supposed  shells 
of  unicelled  plants),  some  perfect,  more  broken,  most  of  all  completely 
disintegrated  (Fig.  757).  The  flint-nodules,  similarly  examined  by  sec- 
tion, show  spicules  of  sponge  and  siliceous  shells  of  Diatoms.  Chalk 

such  as  described  was  supposed  to  be 
found  nowhere  except  in  Europe,  but 
recently  good  chalk  composed  of  Fora- 
miniferal  shells,  and  containing  flints, 
has  been  found  in  Texas  (Hill).  Figs. 


FIG.  756.— Chalk-Cliffs  with  Fliut-Nodules. 


FIG.  757. 


Q) 


FIG.  758. 


FIG.  759. 


FIG.  760. 


FIG.  761. 


FIGS.  757-761.— FORAMINIFERA  OF  CHALK:  757.  Chalk  as  seen  under  the  Microscope  (after  Nichol- 
ppn).  758.  Cuneolina  pavonia.  759.  Flabellina  rugosa.  760.  Lituola  nautiloides.  761.  Chrysa- 
lidina  gradata  (after  D'Orbigny). 

758-761  represent  some  of  the  more  common  Rhizopods  found  in 
chalk. 


472 


MESOZOIC  ERA- AGE   OF  REPTILES. 


Origin  of  Chalk. — A  material  so  unique  must  have  been  formed 
under  peculiar  conditions.  Eecent  investigations  have  shown  that 
chalk  is  a  deep-sea  ooze.  In  all  the  deep-sea  soundings  and  dredgings 
recently  undertaken,  it  is  found  that  the  sea-bottom  between  the  depths 
of  3,000  and  20,000  feet,  where  not  too  cold,  is  a  white  ooze,  consisting 
mainly  of  Ehizopod  shells  (Globigerina,  Radiolaria,  etc.)  and  Coccoliths, 
Coccsopheres,  etc.,  through  which  are  scattered  silicious  shells  of  Dia- 
toms. These  shells  are  in  every  stage  of  change :  some  living,  or  at 
least  still  retaining  sarcode;  some  perfect,  though  dead  and  empty; 
some  broken ;  most  of  them  completely  disintegrated  into  an  impalpa- 
ble mud.  From  the  great  abundance  of  one  genus  of  Rhizopods,  this 
calcareous  mud  has  been  called  Globigerina  ooze.  In  deep-sea  bottoms, 
therefore,  chalk  is  now  forming.  Also,  strange  to  say,  many  Sponges, 
and  Starfishes,  and  Echinoids,  and  Crustaceans,  very  similar  to  those 
found  in  the  chalk  of  Cretaceous  times,  have  been  brought  up  from 
present  deep-sea  bottoms. 


FIG.  762.— Shells  of  Living  Foraminifera:  a,  Orbnlina  nniversa,  in  its  perfect  condition,  showing  the 
tubular  spines  which  radiate  from  the  surface  of  the  shell;  5,  Globigerina  bulloides,  til  its  ordi- 
nary condition,  the  thin  hollow  spines  which  are  attached  to  the  shell  when  perfect  having  been 
broken  off;  c,  Textularia  variabilis;  d,  Peneroplis  planatus;  e,  Rotalia  concamerata; /,  Cristel- 
laria  subarcuatula.  (Fig.  a  is  after  Wyville  Thomson;  the  others  are  after  Williamson.  All  the 
figures  are  greatly  enlarged.) 

There  seems  little  doubt,  therefore,  that  chalk  is  a  deep  sea-bottom 
formation.  The  flint-nodules  have  been  formed  by  a  subsequent  process 
similar  to  that  which  gives  rise  to  other  nodules  (p.  188).  The  silica, 
which  in  the  ooze  was  at  first  scattered,  is  slowly  aggregated  into  pure 


CRETACEOUS  PERIOD.  473 

flint-nodules,  and  the  matrix  is  left  in  a  condition  of  pure  carbonate 
of  lime.* 

Extent  of  Chalk  Seas  of  Cretaceous  Times  in  Europe.— Chalk  of 
nearly  homogeneous  aspect  prevails  from  the  north  of  Ireland  through 
Middle  Europe  to  the  Crimean  and  Caucasus,!  a  distance  of  1,140 
miles ;  and,  in  the  other  direction,  from  the  south  of  Sweden  to  the 
south  of  Bordeaux,  a  distance  of  840  miles  (Lyell).  It  is  evident, 
therefore,  that  at  that  time  a  deep  sea  occupied  a  large  portion  of 
Central  Europe.  The  white  chalk  of  England  and  France  is  about 
1,000  feet  thick.  When  we  remember  the  mode  in  which  it  has 
been  formed,  this  thickness  indicates  an  almost  inconceivable  lapse  of 
time. 

Cretaceous  Coal. — Coal  is  again  found  in  large  quantities  in  rocks 
of  this  period  in  the  United  States.  The  mode  of  occurrence  is  simi- 
lar to  that  found  in  rocks  of  other  periods;  but  as  most  of  this 
coal  is  found  in  the  Laramie,  and  as  this  is  a  transition  group  to 
the  Tertiary,  we  shall  put  off  the  discussion  to  the  end  of  the  Creta- 
ceous. 

Subdivisions  of  the  Cretaceous. — In  the  localities  where  the  Ameri- 
can Cretaceous  was  first  well  studied,  viz.,  in  New  Jersey  and  in  the 
western  Plains  and  Plateau  region,  the  lower  part  of  the  series  was 
wanting,  and  hence  a  great  gap  was  supposed  to  exist  here  in  the 
American  geological  record.  But  recently  the  Lower  Cretaceous  has 
been  found  in  many  widely-separated  regions  and  by  different  observ- 
ers, viz.,  in  California,  by  Whitney  (Shasta  group) ;  in  Texas,  by  Hill 
(Comanche  group) ;  J  in  Canada,  by  Dawson  (Kootani  group) ;  and  on 
the  Atlantic  border,  by  McGee  (Potomac  group).**  The  Comanche 
group  of  Hill  is  probably  the  most  complete,  and  we  therefore  adopt 
this  name.  It  is  probable  that  the  lowest  of  Hill's  Comanche  group 
viz.,  Trinity  beds,  may  be  Uppermost  Jurassic. 

The  .Cretaceous  series  may  be  conveniently  divided  into  Upper, 
Middle,  and  Lower.  The  subdivisions  of  these  are  of  course  local.  In 
Europe  the  Tertiary  is  nearly  everywhere  unconformable  on  the  Cre- 
taceous, showing  a  gap  at  this  horizon ;  in  America  this  gap  is  com- 
pletely filled  in  the  West  by  a  transition  group  called  the  Laramie. 
The  relation  between  the  main  divisions  of  the  American  Cretaceous  on 
the  interior  plains  and  Atlantic  border,  and  of  both  with  the  European 
Cretaceous,  as  shown  in  the  following  table : 

*  Wallace  thinks  that  chalk  is  a  coral  mud  formed  in  warm  seas  full  of  foraminiferal 
life  (Island  Life,  p.  84). 

f  Favre,  Archives  des  Sciences,  vol.  xxxvii,  p.  118  el  seq.  * 

\  Marcou  had  long  ago  (1853)  discovered  Neocomian  in  New  Mexico,  but  the  discovery 
was  not  recognized  by  American  geologists. 

*  This  is  probably  a  transition  to  Jurassic. 


474 


MESOZOIC   ERA— AGE   OF   REPTILES. 


LOWER  TEBTIAKY. 

AMERICAN. 

EUROPEAN. 

WESTERN  PLAINS. 

ATLANTIC  BORDER. 

Wahsatch  and  Puerco  beds. 

Eo-lignitic. 

Plastic  clay,Thanet  sands. 

Transition. 

Laramie. 

Wanting. 

Wanting. 

Cretaceous. 

TTnnPr  -S  Foxhi11  grouP- 
er  (  Colorado  group. 

Middle.  Dakota  group. 
Lower.  Comanche  group. 

N.  J.,  Penn.,  and 
Miss. 

Wanting. 
Wanting. 

j  White  chalk. 
|  Gray  chalk. 
\  Upper  Greenland 
1      Gault. 
Xeocomian. 

Transition. 

Trinity  beds. 

Potomac  formation. 

Wealden. 

Upper  Jurassic. 

Baptanodon  beds. 

Wanting. 

Purbeck. 

Life-System:  Plants. 

Leaf-impressions  are  very  abundant  in  the  American  Cretaceous, 
and  the  most  cursory  examination  reveals  at  once  a  type  of  plants  not 
seen  in  any  lower  rocks,  viz.,  Angiosperms,  both  Dicotyls  and  Palms. 
We  have  said  that  the  Sierra  revolution  at  the  end  of  the  Jura-Trias 
produced  important  changes  in  America.  A  great  break  in  the  record 
occurs  at  this  time  in  the  region  (the  Plains)  where  these  plants  were 
found.  When  the  record  commences  again  in  the  Dakota  epoch  we 
observe  a  very  great  difference  in  the  subject-matter.  The  whole  as- 
pect of  field  and  forest  must  have  been  different  and  much  more  mod- 


FIG.  765. 


763.  FIG.  764. 

FIGS    763-765.—  CRETACEOUS  PLANTS,  DAKOTA  GROUP  (after  Lesquerenx):    763.  Liquidambar  in- 
tegrifolium.    764.  Laurus  Nebrascensis.    765.  Quercus  primordialis.    All  reduced. 


CRETACEOUS  PLANTS. 


475 


FIG.  767. 


Fio.  766. 


FIG.  768. 


FIG.  770. 

FIGS.  766-770.— CRETACBOUS  PLANTS,  DAKOTA  GROUP  (after  Lesquereux):  766.  Sassafras  Mudeei. 
767.  Sassafras  araliopsis.  768.  Salix  proteaefolia.  769.  Fagus  polyclada.  770.  Prctophyllum 
quadratum.  All  reduced. 

ern.  Nearly  all  the  genera  of  our  modern  trees  are  present,  e.  g.,  Oaks, 
Maples,  Willows,  Sassafras,  Dogwood,  Hickory,  Beech,  Poplar,  Tulip- 
tree  (Liriodendron),  Walnut,  Sycamore,  Sweet-gum  (Liquidambar), 
Laurel,  Myrtle,  Fig,  etc.  Out  of  213  species  of  plants  found  in  the 
Dakota  group,  about  180  species  are  Dicotyls  (Ward)  and  at  least  half 
of  these  belong  to  living  genera  (Lesquereux).  And  if  we  include 


476 


MESOZOIC  ERA— AGE   OF  REPTILES. 


FIG.  771. 


FIG.  772. 


FIG.  774. 

FIGS.  771-775. — PLANTS  op  THE  POTOMAC  FORMATION  (after  Fontaine):  Conifers.  771.  Baieropsis 
foliosa.  772.  Sequoia  ambigna:  a,  Leafy  branch;  b,  Cone.  Dicotyledons.  773.  Araliaephyllum 
obtusilobum,  x  §.  774.  Hedercephyllnm  angulatum,  x  §.  775.  Sassafras  cretaceum,  x  §. 


CRETACEOUS  ANIMALS. 


477 


the  Laramie  in  the  Cretaceous  we  may  add  226  more  species  to  the 
list,  but  these  latter  are  quite  different  and  Tertiary  in  type.  A  few 
Palms  have  also  been  found  in  Vancouver's  Island. 

It  is  a  noteworthy  fact  that  many  of  the  most  characteristic  Creta- 
ceous genera,  and  those  most  abundant  and  varied  in  species  at  that 
time,  are  now  represented  by  only  one  or  two  species.  For  example, 
there  are  now  only  two  species  of  Sassafras ;  two  or  three  species  of 
Plane-tree ;  one  of  Liriodendron ;  and  two  of  Liquidambar.  These 
are  evidently  the  remnants  of  an  extinct  flora. 

Origin  of  Dicotyls. — The  appearance  of  these,  the  highest  order  of 
plants,  in  fully  differentiated  forms,  seems  sudden  and  without  pro- 
genitors. But  the  obvious  reason  is,  that  there  is  here  a  great  loss  of 
record.  The  gap  is  now  filled  by  the  discovery  of  the  Comanche 
group ;  and  in  the  lowest  part  of  this  group  on  the  Atlantic  border 
(Potomac  formation),  have  recently  been  found  and  described  by  Fon- 
taine 350  species  of  plants  mostly  of  Jurassic  types  (Conifers,  Cycads, 
and  Ferns),  but  among  them,  and  from  the  upper  part  of  the  forma- 
tion, 7G  species  of  Dicotyls.  These  earliest  known  Dicotyls,  though  of 
very  generalized  character  sp  far  as  genera  and  families  are  concerned, 
are  yet  well-differentiated,  unmistakable  Dicotyls.  We  must,  there- 
fore, look  still  lower  for  their  point  of  origin  and  for  connecting  links 
with  other  classes.  These  important  discoveries  leave  us  still  in  doubt 
as  to  the  class  of  previously- 
existing  plants  from  which 
they  may  have  sprung. 

But  if  the  highest  plants, 
the  Dicotyls,  are  abundant,  so 
are  also  the  lowest  Proto- 
phytes,  or  uni-celled  plants. 
Diatoms,  Desmids,  Cocco- 
spheres,  are  abundant  in  the 
chalk  of  Europe. 

Animals. 

Protozoa.  —  As  already 
stated,  chalk  is  made  up  al- 
most wholly  of  shells  of  Fo- 
raminiferae  (Rhizopods)  and 
of  certain  uni-celled  plants. 
According  to  Ehrenberg,  a 
often 


FIG.  776.  FIG.  777. 

Contains    PlGg    ^    777. -CRETACEOUS   SPONGES:  776.  Siphc 

flCUS.       '"'•"•'      ••»•-_*_:-_,.*-..   -  = ,__ 


cubic    inch 

millions    of      microscopic    Or-  flcu8'    777-  Ventriculites  simplex. 

ganisms.     More  than  120  species  of  Foraminifers  have  been  found  in 
the  English  chalk  alone.     Some  of  these  seem  to  be  species  still  living 


478 


MESOZOIC  ERA— AGE   OF  REPTILES. 


in  deep  seas.  These  are  all  extremely  minute,  but  some  of  larger  size 
are  found  in  the  Cretaceous  limestone  of  Texas.  Those  from  the  chalk 
have  already  been  given  (p.  471). 

Sponges  are  extremely  common  in  the  chalk,  as  they  are  also  in 
deep-sea  bottoms  of  the  present  day.  About  one  hundred  have  been 
found  in  the  chalk. 

Echinoderms. — The  free  Echinoderms  are  now  for  the  first  time  in 
excess  of  the  stemmed.  The  EcMnoids  are  especially  abundant  and 


FIG.  779. 


FIG.  780. 


FIGS.  778-780.— ECHINOIDS  OF  THE  CRETACEOUS  op  EUROPE:  778.  Galerites  albogalerus.    779.  Dis- 
coidea  cylindrica.    780.  Goniopygus  major. 

decidedly  modern  in  type ;  and  in  the  chalk  some  genera  are  identical 
with,  and  some  species  very  similar  to,  those  recently  got  from  deep- 
sea  ooze.  The  above  are  from  the  European  Cretaceous. 


FIG.  781. 


FIG.  782. 


FIGS.  781,  782.— LAMELLIBRANCHS:  781.  Ostrea  Idriaeneis  (after  Gabb).    782.  Inoceramus  dimidiue 

(after  Meek). 

Mollusks. — For  the  first  time  Lamellibranclis  are  fairly  in  excess  of 
Brachiopods.  Among  the  latter  the  modern  family  of  Terebratulce  are 
especially  conspicuous.  Among  the  former  the  most  noteworthy  fact 
is  the  abundance  of  the  Oyster  family — Ostrea^  Gryplicea,  Exogyra, 
etc. ;  and  the  Avicula  family,  Avicula,  Inoceramus^  etc.,  some  of  which 
are  of  great  size. 


CRETACEOUS  ANIMALS. 


479 


Fiu.  784. 


Fio.  785. 


Fio.  787. 


FIG.  783. 


FIG.  786. 


Fio.  788. 


Fros.  783-783.— COMANCHE  SHELLS  (after  White):  783.  Gryphaea  Pitcheri.  784.  Exogyra  Texana. 
785.  Aucella  Erringtonii,  Knoxville  group,  Cal.  786.  Aucella,  side  view.  787.  Requienia  pata- 
giata.  788.  Requienia  Texana. 


480 


MESOZOIC  ERA— AGE   OF   REPTILES. 


Two  very  strange  and  characteristic  groups  of  bivalve-shells  occur 
here,  and  are  very  abundant,  viz.,  the  Rudistes  or  Hippuritidw  and  the 

Chamidce.  In  the  former,  one  valve  is  small 
and  often  flat,  while  the  other  is  enormously 
elongated  like  a  cow's  horn.  In  the  latter 
one  or  both  valves  are  elongated,  and  often 
coiled  in  the  manner  of  a  rarn's  horn.  We 
give  some  figures  (789-792)  from  foreign 
localities  and  some  (787,  788)  from  our  own 
country. 

Among  Gasteropoda  (Figs.  793-795),  the 
beaked  or  siphonated  kinds  are  now  for  the 
first  time  abundant,  as  in  the  present  seas. 


FIG.  791. 


FIG.  790. 


FIG.  792. 


FIGS.  789-792.— 789.  Hippurites  Toucasiana,  a  large  individual  with  two  small  ones  attached  (after 
D'Orbigny).  790.  Section  of  a  Radiolites  cylindriasus,  showing  structure.  791.  Upper  Valve  of 
Radiolites  mammelaris.  792.  Caprina  adversa  (after  Woodward). 

Among  Ceplialopods  the  Ammonites  and  Belemnites  still  continue 
in  great  numbers  and  size,  but  they  die  out  at  the  end  of  this  period 
forever.  In  the  Cretaceous  of  the  Western  Plains  some  Ammonites 
have  been  found  over  three  feet  in  diameter  (Dana).  This  family 
seemed  to  have  reached  its  culmination  just  before  its  extinction.  But 
what  is  still  more  remarkable  is  the  introduction  of  many  new  genera 
of  very  strange  and  unexpected  forms.  These  are  sometimes  partly 
uncoiled^  as  in  ScapMtes  (boat),  Criocera's  (ram's-horn),  Toxoceras 
(bow-horn),  Ancyloceras  (hook-horn),  Hamites  (hook) ;  sometimes 
completely  uncoiled,  as  in  Baculites  (walking-stick) ;  sometimes  coiled 


CRETACEOUS  ANIMALS. 


481 


spirally,  like  a  Gasteropod,  as  in  Turrulites  and  Helioceras.     Belem- 
nites  (Fig.  796)  also  continue,  though  in  diminishing  numbers. 

These  strange  forms  have  been  likened  by  Agassiz  to  death-contor- 
tions of  the  Ammonite  family ;  and  such  they  really  seem  to  be.    From 


FIG.  793. 


FIG.  794. 

FIGS.  793-795.— CRETACEOUS  GASTEROPODS:  793.  Cyprsea  Matthewsonii  (after  Gabb).     794.  Apor- 
rhuis  falciformis  (after  Gabb).    795.  Scalaria  Sillimaui  (after  Lesquereux). 

the  point  of  view  of  evolution,  it  is  natural  to  suppose  that  under  the 
gradually-changing  conditions  which  evidently  prevailed  in  Cretaceous 
times,  this  vigorous  Mesozoic  type  would  be  compelled  to  assume  a 
great  variety  of  forms,  in  the  vain  attempt  to  adapt  itself  to  the  new 
environment,  and  thus  to  escape  its  inevitable  destiny.  The  curve  of 
its  rise,  culmination,  and  decline,  reached  its  highest  point  just  before 


FIG.  796.— Belemnites  impressus  (after  Gabb). 


it  was  destroyed.     The  wave  of  its  evolution  crested  and  broke  into 
strange  forms  at  the  moment  of  its  dissolution. 

Among  Crustaceans,  the  Brachyurans,  short-tailed  Crustaceans 
(crabs),  which  were  barely  introduced  in  the  Jurassic,  are  here  repre- 
sented by  several  genera. 

31 


482 


MESOZOIC   ERA— AGE   OF  REPTILES. 


FIG.  800. 


FIG.  801. 


FIG.  802. 


FIGS.  797-803.— CRETACEOUS  CEPHALOPODS:  797.  Ammonites  Chicoensis  (after  Gabb).  798.  Scaphi- 
tes  sequalis  (after  Pictet).  799.  Crioceras,  restored  (after  Pictet).  800.  Helioceras  Robertianua 
(after  Pictet).  801.  Ancyloceras  percostatue.  x  4  (after  Gabb),  802.  Baculites  anceps,  x  £  (after 
Woodward).  803.  Turrulites  catenatus  (after  D?Orbigny). 

Vertebrates — Fishes. — In  the  development  of  this  class  some  de- 
cided steps  in  advance  are  here  recorded.  Placoids  and  Ganoids  still 
continue,  but  Teleosts,  or  true  typical  modern  fishes,  are  here  intro- 
duced for  the  first  time,  and  in  considerable  numbers,  and  some  of 
gigantic  size,  These  earliest  Teleosts  were  related  to  salmon,  herring, 
perch,  pike,  etc.  Beryx,  a  genus  still  found  in  open  seas,  is  found  in 
the  Chalk  of  Europe  and  Upper  Cretaceous  of  America.  Among  Pla- 
coids,  too,  although  the  Cestracionts  and  Hybodonts  continue  (the  lat- 
ter, however,  passing  out  with  the  Cretaceous),  the  modern  type,  the 
true  sharks  or  Squalodonts,  having  lancet-shaped  teeth,  are  for  the 
first  time  abundant.  We  give  figures  of  Cestraciont  and  Squalodont 


CRETACEOUS  ANIMALS. 


483 


teeth,  and  also  a  tooth,  natural  size,  of  a  gigantic  pike,  eight  feet  long, 
from  American  Cretaceous,  and  a  restoration  of  the  same  by  Cope ; 
also,  two  Teleosts  from  European  Cretaceous. 


FIG.  805. 


FIG.  806. 


FIGS.  804-806— CRETACEOUS  FISHES—  Placoids /  804.  Otodus  (after  Leidy).     805,  Ptychodns  Mor- 
toni  (after  Leidy).     Teleosts :  806.  Portheus  molossus— Tooth,  natural  size  (after  Cope). 

The  Hybodonts  were  essentially  a  Mesozoic  type ;  the  Squalodonts 
are  essentially  Tertiary  and  modern.  The  two  types  coexist  in  the  Cre- 
taceous, the  former  passing  out,  the  latter  increasing,  and  finally  dis- 
placing the  former.  The  accompanying  figure  (Fig.  810)  represents  the 
succession,  rise,  culmination,  and  decline  of  the  three  families  of  sharks. 

Cope  gives  ninety-seven  species  of  North  American  Cretaceous 
fishes  known  in  1875.  Of  these,  if  we  include  the  Chimera  family,  an 
aberrant  type  of  Placoids  very  common  in  the  Cretaceous,  forty-five 
were  Placoids.  The  rest  are  mostly  Teleosts,  for  the  Ganoids  are  rap- 


484 


MESOZOIC  ERA— AGE   OF   REPTILES. 


Fio.  809. 

S07-8Q9.  ^CRETACEOUS  FISHES—  TeUosts ;  807.   Portheue,  restored,  x 
JJeryx  Lewesiensis.    809.  Osmeroides  Mantelli. 


(after  Cope).    808. 


idly  disappearing.     In  Europe,  twenty-five  genera  of  Cycloids  and  fif- 
teen of  Ctenoids  are  found  in  the  Cretaceous  (Dana). 

Palaeozoic  Meeozoic  Cenozoic 


FIG.  810.— Diagram  representing  the  Distribution  in  Time  of  Placoids. 

Reptiles. — This  class  seems  to  have  culminated  about  the  end  of 
the  Jurassic  or  the  beginning  of  the  Cretaceous  period.  If  their  re- 
mains are  more  abundant  in  the  Jurassic  in  Europe,  they  are  far  more 
abundant  in  the  uppermost  Jurassic  (Atlantosaur  beds)  and  in  the  Cre- 
taceous in  America.  In  fact,  we  had  here  in  America  during  the  Cre- 
taceous an  extraordinary  abundance  and  variety  of  reptilian  life,  in- 
cluding all  the  principal  orders  already  mentioned,  viz.,  EnaUosaurs, 


CRETACEOUS  ANIMALS. 


485 


Dinosaurs,  Pterosaurs,  and  Crocodilian*,  and  also  a  new  type,  intro- 
duced in  the  Cretaceous  for  the  first  time,  the  Mosasaurs,  wholly  ma- 
rine in  habits,  but  of  long,  slender,  snake-like  form,  and  attaining 
extraordinary  length.  Turtles  were  also  found  in  large  numbers  and 
of  great  size.  We  can  mention  only  a  very  few  of  the  most  remarkable 
of  the  Cretaceous  reptiles. 


A 


FIG.  811.-Teeth  of  Hadrosaurus  (after  Leidy):  a,  Pavement  of  Teeth;  b  and  c,  Tooth  separated. 

Among  Enaliosaurs  the  Ichthyosauridce  are  not  found  in  America, 
but  the  PlesiosauridcB  were  abundant,  and  attained  much  greater  size 
than  in  Europe.      Leidy  describes  one,  Discosaur  (Elas- 
mosaur,  of  Cope),  which  was  fifty  feet  long,  with  a  neck 
of  sixty  vertebra  and  twenty-two  feet  long.     Among 
Dinosaurs  the  Hadrosaur  from  New  Jer- 
sey was  twenty-eight  feet  long ;  and,  judg- 
ing from  the  huge  size  of  its  hind-legs  and 
massiveness  of  its  hips  and  small  size  of  its 
fore-legs,   it  seems   to  have  been   able   to 
stand  and  walk  in  the  manner  of  birds 
(Fig.  813).     This  animal  was  a  vegeta- 
ble feeder,  with  teeth  somewhat  like 
those  of  the  Iguanodon,  but  set  in  sev- 
eral rows,  so  as  to  form  a  kind  of  tes- 
sellated pavement  (Fig.  811).      From 
the  same  locality  the  Dryptosaurus 
(Lalaps),  similar  to  the  Megalo- 
saur,  and  twenty-four  feet  long, 
and  the  Ornithotarsus  (bird- 
shank),  thirty  -  five  feet  long, 
stood  twelve  to  fifteen  feet  high 
when  walking  on  their  hind-legs.     Among  Pterosaurs,  Marsh  has  found 
in  the  Western  Cretaceous  the  remains  of  at  least  seven  species,  two  of 


FIG.  812.—  Hadrosaurts  (restored  by  Hawkins). 


486 


MESOZOIC  ERA— AGE  OF  REPTILES. 


which  were  twenty  to  twenty-five  feet  in  alar  extent,  and  another  eigh- 
teen feet. 

The  American  Pterosaurs  differ  from  all  other  known  Pterosaurs 
in  the  fact,  recently  brought 
to  light  by  Marsh,  that  their 
jaws  were  entirely  toothless, 
and  probably  sheathed  with 
horn,  as  in  birds.  They  have 
therefore  been  placed  by 
Marsh  in  a  distinct  order, 
Pteranodontia,  from  the 
type  genus  Pteranodon 
(winged- toothless).  Proba- 
bly all  the  American  Ptero- 
saurs belong  to  this  order. 
One  of  them,  P.  ingens,  had 

.   toothless  jaws  four  feet  long, 

x   and  an  expanse  of  wing  of 

«   twenty-two  feet. 

5         Among  the  many  Chelo- 

£   nians  (turtles)  found  in  the 

I    Cretaceous  of  the  Western 

s    Plains,  of  the  Kocky  Mount- 

f  ain  region,  and  of  New  Jer- 

«   sey,  one,  the  Atlantochelys 

§,  gigas,  had  a  length  of  near- 

|   ly    thirteen     feet,    and     a 

|   breadth  across  the  extended 

|   nippers     of      fifteen     feet 

w    (Cope).      The  structure  of 

g   this  huge  turtle  was  singu- 

o   larly  embryonic.      The  flat- 

^  tened  ribs,  which  by  their 
coalescence  make  the  greater 
part  of  the  shell  of  a  turtle, 
were  in  this  species,  as  in 
the  embryo  of  modern  tur- 
tles, not  yet  coalesced. 

But  the  most  remarka- 
ble and  characteristic  rep- 
tiles found  in  the  Cretaceous 
are  the  Mosasaurs  (Pytho- 
nomorpha  of  Cope).  The 
first  specimen  of  the  order 


CRETACEOUS   ANIMALS. 


487 


was  found  in  Europe,  on  the  river  Meuse,  and  hence  the  name  Mosa- 
saurs ;  but  they  seem  to  have  been  far  more  abundant  in  America.  At 
least  fifty  species  (Cope)  have  been  found  in  the  Cretaceous  of  New 
Jersey,  the  Gulf  States,  and  Kansas.  Of  these,  the  Mosasaurus  prin- 


FIG.  817. 


TIGS.  815-^17.— 815.  Snout  of  aTylosaurus  micromus,  x  \  (after  Marshl.  816.  A.  Scapular  arch  and 
fore-limbs  of  Lestosaurus  simus  (after  Marsh),  seen  from  below,  one  sixteenth  natural  size, 
with  outline  of  sternum  from  Edestosaurus.  B.  Pelvic  arch  and  hind-limbs  of  Lestosaurns 
simus,  seen  from  below.  One  twelfth  natural  size.  il.  ilium;  pb,  pubis;  in,  ischinm;  /,  femur; 
t,  tibia;  f,  fibula;  mt,  metatarsal.  The  paddles  are  represented  as  horizontal,  and  the  bones  of 
the  arches  are  somewhat  displaced  to  bring  them  into  the  same  plane.  817.  Tooth  of  a  Mosa- 
saurus, x  i  (after  Leidy). 

ceps  was  sixty  to  seventy  feet  long,  and  Tylosaurus  (Liodori)  dyspelor 
probably  "attained  a  length  equal  to  the  longest  whale"  (Cope). 
These  reptiles  seem  to  have  united  the  long,  slender  form  of  a  snake, 


488  MESOZOIC   ERA— AGE   OF   REPTILES. 

and  the  short,  strong,  well-fingered  paddles  of  a  whale,  with  the  essen- 
tial characters  of  a  lizard.  Another  snake-like  character  possessed  by 
this  order  was  rows  of  teeth  on  the  palatal  bones,  in  addition  to  those 
in  the  jaws ;  and  a  peculiar  joint  in  the  lower  jaws,  by  means  of  which, 
when  aided  by  the  recurved  teeth,  the  jaws  could  act  separately  like 
arms,  in  dragging  down  their  throats  prey  which  was  too  large  to  swal- 
low directly  (Fig.  818). 


FIG.  818.— Jaw  of  an  Edestosaurus  (Clidastes),  x  £  (after  Cope). 

We  give  on  page  486  a  restoration  by  Cope  of  one  of  the  most 
slender  forms — Edestosaurus — and  also,  on  page  487,  head  and  tooth, 
and  limbs,  of  other  Mosasaurs. 

The  number  of  species  are  yearly  increasing  by  new  discoveries. 
The  remains  of  at  least  fourteen  hundred  individuals  of  Mosasauroids 
alone  are  now  gathered  in  Marsh's  collection. 

According  to  Cope,  147  species  of  reptiles  have  been  described  from 
the  Cretaceous  of  North  America,  of  which  fifty  are  Mosasaurs,  forty- 
eight  Testudinata  (turtles  and  tortoises),  eighteen  Dinosaurs,  fourteen 
Crocodilians,  thirteen  Sauropterygia  (Plesiosaur-like),  and  four  Ptero- 
saurs. At  least  three  more  Pterosaurs  have  been  found,  making  the 
whole  number  seven  (Marsh). 

In  Europe,  Iguanodons,  Teleosaurs,  Ichthyosaurs,  Plesiosaurs,  and 
Pterosaurs  still  continue  in  the  Cretaceous,  some  of  the  last  being 
twenty-five  feet  in  expanse  of  wing ;  and  also  a  few  Mosasaurs  were 
introduced. 

Birds. — The  history  of  the  discovery  of  the  earlier  fossil  birds  is 
instructive.  Until  1858,  with  the  exception  of  the  doubtful  tracks  in 
the  Connecticut  River  sandstone,  no  birds  had  been  found  lower  than 
the  Tertiary.  In  that  year  the  bones  of  a  bird,  probably  related  to  the 
gull,  were  found  in  the  upper  greensand  of  England.  In  1862  the  won- 
derful reptilian  bird  ArcJiceopteryx  macroura,  already  described  (p.  444), 
was  found  in  the  Solenhofen  limestone  of  Germany  (Upper  Jurassic). 
In  1870,  and  subsequently,  Marsh  discovered  in  the  Cretaceous  of  New 
Jersey  and  Kansas  about  twenty  species  of  birds.  Those  from  New  Jer- 
sey were  from  the  Upper  Cretaceous  (Foxhill  group),  and  are  probably 
true  birds — waders  and  swimmers — though  not  of  the  higher  orders. 
Those  from  Kansas  are  from  a  lower  horizon  (Colorado  group— see  table 
on  p.  474),  and  are  all  wonderful,  toothed  birds,  entirely  different  from 
any  existing  order.  With  the  exception  of  the  Archaeopteryx,  these 
are  the  most  extraordinary  birds  yet  discovered.  Some  of  them,  be- 


CRETACEOUS   ANIMALS. 


489 


longing  to  the  two  genera  Ichthyornis  and  Apatornis,  were  without 
the  horny  beak  so  characteristic  of  existing  birds,  but  instead  had  thin. 


FIG.  819.— Restoration  of  Ichthyornis  victor  (after  Marsh).    One  half  natural  size. 

long,  slender  jaivs,  furnished  with  many  sharp,  conical  teeth,  set  in 
sockets,  twenty  on  each  side  below,  and  somewhat  fewer  above  (Fig. 
819).  Their  vertebrae  were  amphicoslous  or  bi-concave,  as  in  fishes  and 
many  extinct  reptiles,  but  in  no  modern  bird  (Fig.  821).  Like  modern 
birds,  however,  they  had  a  keel  on  the  breast-bone  for  the  attachment 
of  the  powerful  muscles  of  flight.  The  tail  also  is  worthy  of  atten- 
tion, being  not  like  that  of  the  Jurassic  Archaeopteryx,  but  much 
shorter  and  not  so  reptilian  (Marsh).  These  birds  were  about  the  size 
of  a  pigeon,  and  were  evidently  powerful  fliers.  Fig.  819  is  a  restora- 
tion by  Marsh  of  one  of  this  type.  The  other  toothed  birds  had  similar 


490 


MESOZOIC  ERA— AGE   OF  REPTILES. 


jaws,  but  their  teeth  were  set  in  grooves  instead  of  distinct  sockets 
(Fig.  822),  and  they  differed  also  in  having  no  keel  and  in  having  ordi- 
nary bird- vertebras  (Fig.  823).  These  were  evidently  divers,  and  in- 
capable of  flight.  Two  of  them — Hesperornis  regalis  and  Lestornis 


FIG.  821. 


FIG.  823. 


FIG.  824. 


FIG.  820. 


FIG. 822. 


FIGS.  820-824 — ODONTORNITHES  (after  Marsh):  820.  Lower  Jaw  of  Ichthyornis  dispar.  x  2.  821. 
Cervical  Vertebra  of  same,  x  2.  822.  Lower  Jaw  of  Hesperornis  regalis,  x  £.  823.  Dorsal  Ver- 
tebra, x  $.  824.  Tooth  of  same,  x  2. 

crassipes — were  of  gigantic  size,  being  from  five  to  six  feet  from  snout 
to  toe.  On  next  page  (Fig.  825)  we  give  a  restoration  by  Marsh  of  this 
remarkable  bird.  In  these  birds,  therefore,  we  have  the  most  extraordi- 


CRETACEOUS  ANIMALS. 


491 


nary  combination  of  bird  characters  with  reptilian  and  fish  characters. 
So  extraordinary  and  exceptional  is  this  combination  of  characters, 


Fro.  825.— Hesperornis  regalia,  x  A  (restored  by  Marsh). 

that  Marsh  believes  he  is  justified  in  placing  them  not  only  in  new 
orders,  but  even  in  a  new  sub-class.  According  to  this  authority,  the 
class  of  Birds  may  be  divided  into  two  sub-classes,  viz.,  Ornithes,  or 
true  birds,  and  Odontornithes,  or  toothed  birds.  And  the  new  sub- 
class Odontornithes  into  three  orders,  viz. :  (1)  Saururce  (reptile-tailed), 
represented  by  the  Archaeopteryx,  (2)  Odontolcce  (teeth  in  grooves), 
represented  by  the  Hesperornis,  and  (3)  Odontotormce  (teeth  in  sock- 
ets), represented  by  the  Ichthyornis.  Yet,  exceptional  as  these  char- 
acters may  seem,  they  are  just  what  the  law  of  evolution  would  lead  us 
to  expect  in  the  earliest  birds.  As  already  stated  (p.  455),  this  branch 
had  not  yet  been  fairly  separated  from  the  reptilian  stem.  It  is  a 
noteworthy  fact  that  these  toothed  birds  lived  at  the  same  time  and 
in  the  same  localities  with  the  toothless  Pterosaurs  mentioned  on 
page  486. 

It  is  a  remarkable  fact  that  in  the  earliest  representatives  of  each 
class  the  brain  is  relatively  very  small.     This  is  true  of  reptiles,  birds, 


4:92 


MESOZOIC  ERA— AGE   OF   REPTILES. 


and  mammals.     We  give  below  figures  taken  from  Marsh,  showing  the 
relative  size  of  the  brain  in  living  and  Cretaceous  birds. 

Mammals. — It  is  a  most  remarkable  fact  that  although  Marsupial 
mammals  have  been  found  in  the  Jurassic,  and  probably  existed  in 

considerable  numbers  then,  yet,  ex- 
cept in  the  Laramie  which  may  be 
regarded  as  a  transition  to  the  Ter- 
tiary, not  one  has  been  found  in 
the  Cretaceous.  We  know  they 
existed  at  that  time,  for  they  are 
found  in  the  Laramie  of  America 
and  in  the  Tertiary  of  both  Europe 
and  America,  and  still  exist  in  Aus- 
tralia and  elsewhere;  and  it  is  a 
well-established  law  in  Paleontol- 
ogy that  if  a  type  becomes  extinct 
it  never  reappears:  Evolution  never 
goes  backward :  Nature  never  re- 
peats herself.  It  is  probable,  there- 
fore, that  during  the  Cretaceous  the 
Marsupials  which  doubtless  existed 
had  been  driven  to  some  other  por- 
tion of  the  earth,  where  we  shall  yet 
find  their  remains  when  our  knowl- 
edge of  the  geology  of  the  globe  is 
more  complete;  and  in  them  we 
shall  also  probably  find  the  transi- 

FIGS.  826,  827.— 826.   Outline  of    the  skull   and     ,.  ,.      . 

brain  -  cavity    of     Ichthyornis  victor  (after    Lions   TO,  Or  earliest  progenitors   01, 
Marsh),  seen  from  above.    Five  sixths  nat-    ,1       m          -\/r  i        <»  -i      m     L' 

urai  size.    827.  Outline  of  the  skuii  and  the  True  Mammals  of  the  Tertiary. 

brain-cavity  of  Sterna  cantiaca  (after  Gme- 

lin),  same  view.    Natural  size,  ol,  olfactory  _, 

lobes  ;  c,  cerebral   hemispheres  ;    op,    optic  Continuity   Of   tllG  Clialfc. 

lobes;  cb,  cerebellum. 

It  is  probable  that  the  deep  At- 
lantic Ocean  bottom,  where  chalk  is  now  forming,  is  continuous  with 
the  chalk  of  England  and  Central  Europe.  In  other  words,  in  Creta- 
ceous times  a  deep  sea  ran  from  the  mid- Atlantic  far  into  what  is  now 
Central  Europe,  and  in  the  whole  of  this  deep  sea  chalk  was  then 
formed.  At  the  end  of  the  Cretaceous  period  the  eastern  part  was 
raised  and  formed  a  portion  of  Europe,  while  the  rest  remained  as 
deep-sea  bottom,  and  continued  to  make  chalk  until  now.  Thus  there 
is  no  doubt  that  in  the  deep  Atlantic,  off  the  coast  of  Europe,  there  has 
been  an  unbroken  continuity  of  cJialTc-malcing  from  the  Cretaceous 
times  until  now.  But  we  have  seen  (p.  478)  that  many  of  the  living 
deep-sea  species  are  identical  with,  and  nearly  all  extremely  similar  to, 
those  found  in  the  chalk  of  Cretaceous  times.  Thus  there  has  been 


FIG.  826. 


FIG.  827. 


CONTINUITY   OF  THE  CHALK. 


493 


not  only  a  continuity  of  chalk-formation,  but  also  to  some  extent  of  the 
chalk-fauna,  to  the  present  time. 

These  facts  were  certainly  unexpected,  but,  so  far  from  shaking  the 
foundations  of  geological  science,  as  some  have  imagined,  they  are  in 
perfect  accordance  with  the  fundamental  principles  of  geological  suc- 
cession properly  understood ;  as  we  now  proceed  to  show  : 

1.  The  facts  of  identity  have  been  exaggerated.  Many  of  the 
Foraminifera  only  are  identical.  Among  Echinoderms  the  identity 
is  generic4  not  specific.  2.  In  comparing  higher  with  lower  species, 
we  find  that  the  lower  species  are  widely  distributed  both  in  space 
(geographically)  and  in  time  (geologically),  and  that  the  continuance 
or  range  in  time  becomes  less  and  less  in  proportion  as  we  rise  in  the 
scale.  Fig.  828  is  constructed  to  illustrate  this  point ;  we  see  that  liv- 


C/FET/1CEOUS 


R     T     /      A     FJ       Y 


QUATERNAR V 


EOCENE          MIOCENE       PLIOCENE    \\&L AC  \CHAM      TEP 


RECENT 


RECENT 


FIG.  828.— Diagram  illustrating  the  Helative  Duration  of  Lower  and  Higher  Species. 

ing  species  of  mammals  extend  back  only  a  little  way  into  the  Quater- 
nary, living  species  of  mollusks  back  to  the  beginning  of  the  Tertiary, 
while  living  species  of  Foraminifera,  as  we  might  expect,  extend  back 
into  the  Cretaceous.  3.  There  is  a  necessary  relation  between  fauna 
and  external  conditions.  Changes  in  the  latter  determine  correspond- 
ing changes  in  the  former.  Now,  deep-sea  conditions  are  evidently 
far  less  subject  to  change — far  more  continuous — than  shallow- water 
and  land  conditions.  For  this  reason,  we  should  expect  deep-sea  faunas 
to  change  very  slowly.  4.  But  this  can  not  affect  the  geological  chro- 
nology, because  this  chronology  rests  almost  wholly  on  the  remains  of 
shallow-water  and  land  animals.  Chalk  is  the  only  profound  sea- 
bottom  formation  certainly  known.  It  is,  therefore,  wholly  exceptional. 
5.  The  reason  it  is  exceptional  is  that,  as  a  broad  general  fact,  the  pres- 
ent continents  have  been,  through  all  geological  times,  steadily  heaved 
upward  out  of  the  ocean,  growing  larger  and  higher ;  and,  therefore, 
the  successive  additions  have  been  nearly  always  shallow  marginal 
bottoms  and  shallow  interior  seas.  That  the  exception  should  occur 
in  Europe  rather  than  in  America,  too,  is  in  keeping  with  the  general 
character  of  the  development  of  the  European  as  contrasted  with  the 
American  Continent.  Chalk  is  also  found  in  Texas ;  but  here  also  was 
a  deep  interior  sea,  an  extension  of  the  Mexican  Gulf.  6.  Conversely, 
the  fact  that  chalk  is  so  exceptional  is  proof  of  the  development  of 


494:  MESOZOIC  ERA— AGE  OF  REPTILES, 

continents  as  indicated  under  the  last  head — proof  that,  as  a  general 
fact,  the  great  inequalities  of  the  earth's  crust,  which  constitute  land- 
surfaces  and  sea-bottoms,  have  remained  substantially  unchanged  in 
position  from  the  first,  while  steadily  increasing  in  vertical  dimensions. 

General  Observations  on  the  Mesozoic. 

The  Mesozoic,  and  especially  the  Jurassic,  is  characterized  by  the  cul- 
mination of  two  great  classes  of  animals,  viz.,  Cephalopod  Molluslcs  and 
Reptiles,  and  one  of  plants,  the  Cycads.  This  is  shown  in  the  diagram 
on  page  283.  The  culmination  of  reptiles  is,  of  course,  its  most  distin- 
guishing characteristic.  That  it  was  pre-eminently  an  age  of  Reptiles, 
may  be  shown  by  a  comparison  of  its  reptilian  fauna  with  that  of  the 
present  day.  There  are  now,  on  the  whole  face  of  the  earth,  only  six 
large  reptiles  over  fifteen  feet  long — two  in  India,  one  in  Africa,  three 
in  America — and  none  over  twenty-five  feet  long.  In  the  Wealden  atfd 
Lower  Cretaceous  of  Great  Britain  alone  there  were  five  or  six  great 
Dinosaurs  twenty  to  sixty  feet  long,  ten  to  twelve  Crocodilians  and 
Enaliosaurs  ten  to  fifty  feet  long,  besides  Pterodactyls,  turtles,  etc. 
(Dana).  Again,  in  the  Cretaceous  of  the  Ujiited  States  alone  the  full- 
ness of  reptilian  life  was  even  greater ;  for  150  species  of  reptiles  have 
been  found,  most  of  them  of  gigantic  size.  Among  these  were  fifty 
species  of  Mosasaurs,  some  seventy  to  eighty  feet  long ;  many  huge 
Dinosaurs,  twenty  to  fifty  feet  long;  besides  Enaliosaurs,  Pterosaurs, 
and  gigantic  turtles  (Cope).  These  are  preserved  !  But  the  known 
fossil  fauna  of  any  period  is  but  a  fragment  of  the  actual  fauna  of  that 
period.  Not  only  did  reptiles  greatly  predominate,  but  the  age  seemed 
to  impress  its  reptilian  character  on  all  other  higher  animals  existing  at 
that  time.  The  birds  were  reptilian  birds,  the  mammals  were  reptilian 
mammals.  All  animals  as  yet  were  oviparous  (birds  and  reptiles)  or 
semi-oviparous  (marsupials). 

That  the  climate  was  then  warm  and  uniform  is  sufficiently  attested 
by  the  character  of  the  fauna  and  flora.  All  great  reptiles  and  all  Cy- 
cads and  Tree-ferns  are  found  now  only  in  tropical  or  sub-tropical  re- 
gions. This  tropical  fauna  and  flora  were  substantially  similar  in  all 
latitudes  in  which  the  strata  have  been  found — even  as  far  north  as 
Spitzbergen  (Nordenskiold).*  During  the  latter  portion  of  the  Creta- 
ceous period,  as  indicated  by  the  abundance  of  deciduous  Dicotyls,  the 
climate  of  North  America  had  become  cooler,  being  about  8°  or  10° 
warmer  than  now. 

Disturbance  which  closed  the  Mesozoic. — The  disturbance  which  in 
America  closed  the  Cretaceous  period  and  the  Mesozoic  era  was  an 
arching  of  the  earth's  crust  over  the  whole  Plains  and  Plateau  region, 

*  Geological  Magazine,  November,  1875. 


LARAMIE,   OR   TRANSITION   EPOCH.  495 

by  which  the  great  interior  Cretaceous  sea,  which  previously  divided 
America  into  two  continents,  was  abolished,  and  the  continent  became 
one.  At  the  same  time  the  Wahsatch  and  Uintah  Mountains  were 
principally  formed,  and  the  eastern  Rocky  Mountain  range  greatly 
elevated.  If  the  end  of  the  Jurassic  was  pre-eminently  a  time  of 
mountain-making  (Sierra  revolution),  the  end  of  the  Cretaceous  was 
pre-eminently  a  time  of  continent-making.  The  disturbance,  as  usual 
with  those  which  close  an  era,  was  probably  to  some  extent  oscillatory — 
i.  e.,  the  continent  was  probably  higher  and  cooler  during  the  latter 
part  of  the  Cretaceous  than  during  the  subsequent  Eocene.  The 
change  of  physical  geography  was  enormous,  and  the  change  of  climate 
was  doubtless  correspondingly  great.  We  ought  to  be  prepared,  there- 
fore, to  find,  with  the  opening  of  the  next  era,  a  very  great  change  in 
the  organisms. 

Laramie,  or  Transition  Epoch. 

In  the  schedule  on  page  474,  we  have  indicated  a  transition  epoch 
called  the  Laramie.  There  has  been  much  controversy  about  the  true 
position  of  these  strata.  SOme  have  put  them  in  the  Tertiary,  some  in 
the  Cretaceous,  and  some  have  regarded  them  as  completely  transitional 
between  the  two ;  while  still  others  would  solve  the  difficulty  by  assigning 
the  lower  part  to  the  Cretaceous  and  the  upper  part  to  the  Tertiary. 
Stratigraphically  the  Laramie  is  continuous  with  the  Cretaceous  below, 
and  in  some  places  also  with  the  Tertiary  above ;  so  that  the  Creta- 
ceous of  the  West  in  some  places  gradates  through  the  Laramie  into  the 
Tertiary  without  break.  This  is  especially  true  in  California,  where 
the  Upper  Cretaceous  gradates  completely  and  without  the  least  break 
through  the  Tejon  group  into  the  Tertiary.  The  difficulty  of  drawing 
the  line  of  separation  on  paleontological  grounds  is  equally  great. 
The  plants  are  decidedly  Tertiary  in  general  aspect,  but  the  animals, 
especially  the  land-animals,  are  as  decidedly  Cretaceous;  the  shells 
meanwhile  passing  from  the  marine  through  brackish- water  into  fresh- 
water forms.  Cretaceous  Dinosaurs  still  linger,  but  Tertiary  types  of 
Plants  have  already  taken  possession.  Many  palseobotanists  claim  it 
for  Tertiary.  Nearly  all  palaeozoologists  put  it  in  the  Cretaceous. 
There  is  little  doubt  that  it  is  really  transitional,  although  probably 
more  closely  allied  with  the  Cretaceous. 

The  explanation  of  these  facts  is  obvious :  We  have  seen  that  at  the 
end  of  the  Cretaceous  the  great  interior  Cretaceous  sea  was  abolished 
by  elevation,  and  its  place  (as  we  shall  see  hereafter)  was  partly  occu- 
pied by  great  fresh- water  lakes.  Now,  this  change  took  place  somewhat 
gradually,  the  oceanic  condition  passing  into  the  lake-condition 
through  an  intermediate  brackish- water  condition  of  isolated  seas,  the 
sedimentation  going  on  all  the  time.  While  oceanic  conditions  pre- 


496 


MESOZOIC  ERA— AGE   OF  REPTILES. 


vailed,  the  deposits  are  undoubtedly  Cretaceous.  When  lake-conditions 
are  fairly  established,  they  are  undoubtedly  Tertiary ;  the  intermediate 
brackish-water  deposits  are  the  Laramie.  But,  as  the  change  was 
gradual  and  the  sedimentation  continuous,  of  course  the  strata  were 

in   places  conformable 
throughout. 

In  regard  to  the 
Life-system  the  expla- 
nation is  similar.  The 
abolition  of  the  interi- 
or Cretaceous  sea  and 
the  unification  of  the 
continent  was  a  great 
event,  and  produced 
very  great  change  in 
physical  conditions. 
There  was,  therefore,  a 
corresponding  change 
in  the  Life-system. 
But  this  was  also  grad- 
ual. The  Cretaceous 
Dinosaurs  still  lingered, 
ready  to  disappear ;  but 
FIG.  829.  as  new  land  appeared 


FIG.  830.  FIG.  831. 

FIGS.  829-831.— 829.  Aralia  digitata.    830.  Leguminositis  arachioides.     831.  Populus  cuneata. 


LARAMIE,   OR  TRANSITION   EPOCH. 


497 


Fio.  882.  FIG.  883. 

FIGS.  832,  833.— 832.  Viburnum  Newberrianum.    833.  AJnus  Grcwiopsis. 

it  was  taken  possession  of  by  new  types  of  Plants,  probably  migrated 
from  the  north :  and  thus  Cretaceous  land-animals  and  Tertiary  land- 
plants  existed  side  by  side.  Meanwhile,  the  marine  shells  by  changing 
conditions  were  most  of  them  destroyed,  but  some  changed  through 
brackish- water  forms  into  fresh- water  forms  of  the  Tertiary.  Some 
of  the  steps  of  this  change  of  molluscan  types  have  been  traced  (White). 

Such  transition  strata  are  of  especial  interest,  and  deserve  separate 
treatment  in  order  to  emphasize  their  transitional  character. 

Area. — From  what  is  said  above  it  is  evident  that  the  Laramie  ex- 
ists over  very  wide  areas  in  the  region  of  the  interior  Cretaceous  sea, 
but  it  is  largely  covered  by  Tertiary  lake  deposits.  It  is,  however, 
exposed  along  the  eastern  base  of  the  Colorado  mountains,  from  Mexico 
northward  far  into  British  America ;  also  in  the  Laramie  plains, 
where  it  is  traversed  by  the  Union  Pacific  Railroad.  This  is  the  typical 
locality  from  which  it  takes  its  name.  On  the  Pacific  coast,  a  part  at 
least  of  the  Tejon  group,  and  also  the  principal  coal-fields  of  California, 
Washington,  and  British  Columbia,  probably  belong  to  this  horizon. 
In  the  typical  locality,  on  the  Laramie  plains,  the  strata  are  several 
thousand  feet  thick.  It  represents,  therefore,  a  long  period  of  time. 

Life-System — Plants. — The  vegetation  was  very  abundant,  and  the 
plants  had  already  assumed  a  Tertiary  aspect.  About  323  species  of 
plants  are  known,  of  which  226  species  are  Dicotyls.  We  give  a  few 
illustrations  of  these  from  Ward  (Figs.  829-833). 

32 


498 


MESOZOIC  ERA— AGE   OF  REPTILES. 


Coal. — Conditions  seem  to  have  been  especially  favorable  for  the 
accumulation  and  preservation  of  the  abundant  vegetation.  Next  to 
the  Carboniferous,  by  far  the  largest  coal-fields  of  the  United  States 
and  of  British  America  belong  to  the  Cretaceous,  and  especially  to  this 
horizon.  The  most  important  of  these  Cretaceous  coals  are  the  follow- 
ing :  1.  A  large  field  covering  the  greater  portion  of  Western  Kansas 
and  Eastern  Colorado.  2.  Another  valuable  field  in  New  Mexico,  of 
almost  equal  size.  3.  Still  another  of  greater  size  in  Dakota,  and  ex- 
tending northward  far  into  British  America.  These  are,  all  of  them, 
on  the  Plains.  4.  On  the  Plateau  a  valuable  field  covers  nearly  the 
whole  of  the  Laramie  plains  in  Wyoming,  and  stretching  to  the  border 
of  Utah.  The  area  of  these  coal-fields  of  the  Plains  and  Plateau  region 
is  not  known,  but  must  be  enormous.  Some  of  the  fields  are  also  of 
extraordinary  richness,  the  seams  being  often  fifteen  to  twenty  feet 
thick.  They  almost  rival  the  great  fields  of  the  Carboniferous,  already 
described.  On  the  Pacific  border  there  are  several  fields,  which  prob- 
ably belong  to  the  same  horizon,  viz. :  1.  Monte  Diablo  and  Corral 
Hollow  coal-field  in  California.  2.  Seattle,  Carbon  Hill,  and  Belling- 
ham  Bay  coals  of  Washington.  3.  Nanaimo  or  Wellington  coals  of 
Vancouver's  Island,  British  Columbia. 

It  is  usual  to  call  all  these  later  coals  Lignites ,  and  to  imagine  that 
they  are  very  inferior ;  but  much  of  the  Laramie  coal  is  of  good  quality, 
and  hardly  distinguishable  in  appearance  from  coal  of  the  Carbonifer- 
ous age. 


FIG.  834. 


FIG.  836. 


FIG.  837. 

FIGS.  834-837.— LARAMIE  SHELLS  (after  White):  834.  Unio  Holmesianns.     835.  Corbicula  fracta. 
836.  Melama  Wyomingensis.    837.  Viviparus  trochif  ormis. 

Animals. — We  give  a  few  characteristic  shells,  taken  from  White 
(Figs.  834-837) ;  but  the  greatest  interest  centers  in  the  Dinosaur  s, 
and  especially  the  recently  discovered  mammals  of  this  epoch.  -As  we 


LARAMIE,   OR   TRANSITION   EPOCH. 


499 


have  already  said,  the  Dinosaurs  still  continued  to  linger,  but  under 
rapidly  changing  conditions,  and  ready  to  disappear.  And  here,  again, 
as  in  the  case  of  Ammonites  (p.  480),  we  observe  that  the  last  survivors 
take  on  strange  and  grotesque  forms.  In  this  class,  also,  as  in  the  case 
of  Ammonites,  the  wave  of  evolution  crested  and  broke  into  strange 
forms  at  the  moment  of  its  dissolution.  The  most  remarkable  of  all 
Dinosaurs  were  the  different  species  of  Triceratops  (three-horned  face, 
Fig.  838).  This  genus  was  characterized  by  the  possession  of  two 


PIG.  838.— Triceratope  flabellatns,  x  &  (after  Marsh),    a,  nasal  opening ;  6,  orbit ;  h,  frontal  horn- 
core  ;  h',  nasal  horn-core  ;  f,  occipital  crest ;  p,  pre-deutary  bone  ;  r,  rostral  bone. 

enormous  horns,  three  feet  long  and  ten  inches  in  diameter  on  the 
frontal  bones,  and  one  of  smaller  size  on  the  nose ;  and  by  a  large  oc- 


Hfe 


FIG.  839.— Diclonius  mirabilis,  x  ^  (after  Cope). 

cipital  crest  projecting  backward  and  outward  and  curving  downward, 
and  fringed  around  with  short  horns  somewhat  in  the  manner  of  the 
horned  lizard  (Phrynosoma).  The  end  of  the  snout  also  was  toothless, 
and  covered  with  horn  forming  a  beak.  A  head  of  one  of  these  has 
been  found  more  than  six  feet  long  and  four  feet  wide,  and  another 


500  MESOZOIC  ERA— AGE   OF  REPTILES. 

eight  feet  long.  It  was  probably  the  hugest  of  the  huge  animals  of 
this  order. 

Another  strange  Dinosaur  of  this  time  was  the  Diclonius  mirabilis 
of  Cope  (Fig.  839).  This  was  a  huge  bipedal  herbivore,  thirty-eight 
feet  long,  and  head  three  and  a  half  feet,  with  curious  spoon-bill  like 
beak  and  magazines  of  numerous  teeth  (two  thousand  in  all),  somewhat 
like  those  of  the  Hadrosaur  (p.  485). 

Mammals. — The  great  gap  between  the  Jurassic  and  Tertiary  mam- 
.mals  mentioned  on  page  492  has  only  very  recently  (1889)  been  partly 
filled  by  the  discovery  by  Marsh  of  twenty-four  species  of  mammals 
from  the  Laramie.  The  teeth  of  two  of  the  most  characteristic  species 
are  given  in  Figs.  840  and  841.  These  very  important  discoveries  of 


FIG.  840.  FIG.  841. 


FIGS.  840  and  841.— LARAMIE  MAMMALS  (after  Marsh).    840.  Cimolomys  gracilis,  x  3.    841.  Halo- 
don  sculptus,  x  2. 

Marsh  were  supposed  to  be  unique.  But  during  the  present  year 
(1890)  Lemoine  has  found  at  Cernay,  France,  a  mammalian  fauna  in 
which  Metatheres,  extremely  similar  to  those  of  the  Laramie,  are  asso- 
ciated with  Eutheres  characteristic  of  the  lowest  Tertiary  (Puerco- 
beds).*  Thus  the  connection  of  the  Laramie  with  the  Tertiary  is  made 
still  closer.  But  the  gap  still  remains ;  we  still  look  in  vain  for  the 
progenitors  of  the  Tertiary  mammals.  They  will  doubtless  yet  be 
found  in  the  Cretaceous  and  probably  in  the  Laramie  of  this  or  pos- 
sibly some  other  country,  from  which  they  migrated  at  the  beginning 
of  the  Tertiary. 

*  Bulletin  Geological  Society  of  France,  vol.  xviii,  pp.  219,  321  (1890). 


. 

'CEKOZOIC   ERA— AGE  OF   MAMMALS.  501 

CHAPTER  V. 

CENOZOIC  ERA— AGE  OF  MAMMALS. 

THIS  deserves  the  rank  of  a  distinct  era,  and'  the  corresponding 
rocks  that  of  a  distinct  system,  because  there  is  here  a  great  break  in 
the  rock-system,  and  a  still  greater  break  in  the  life-system.  Between 
the  rocks  of  the  Cretaceous  and  Tertiary  there  is,  in  Europe,  almost 
universal  unconformity  In  America,  on  the  contrary,  especially  on  the 
Western  Plains  and  in  California,  there  seems  to  be  in  some  places  a 
continuous  series  of  conformable  rocks  connecting  the  two  eras  (Hay- 
den).  The  record  seems  to  be  continuous.  Yet  here,  no  less  than  in 
Europe,  there  is  at  a  certain  horizon  a  rapid  and  most  extraordinary 
change  in  the  life-system.  This  it  seems  impossible  to  explain  on  the 
theory  of  evolution  unless  we  admit  periods  of  rapid  evolution.  The 
reason  why  there  is  no  general  unconformity  in  America  is,  evidently, 
that  the  movement  here  was  continental,  and  not  mere  mountain-mak- 
ing and  strata-crushing.  Such  continental  movements,  however,  would 
produce  very  great  changes  in  climate,  and  therefore  in  organic  forms. 
The  end  of  the  Jurassic  was  a  period  of  mountain-making,  and  there- 
fore of  unconformity — the  end  of  the  Cretaceous,  a  time  of  continent- 
making,  and  but  little  unconformity,  but  very  great  change  of  climate. 
Therefore,  although  the  interval  lost  in  America  seems  greater  at  the 
end  of  the  Jurassic,  the  change  of  fauna  and  flora  was  far  greater  at 
the  end  of  the  Cretaceous. 

General  Characteristics  of  the  Cenozoic  Era.— As  indicated  by  the 
name,  modern  history  commences  here ;  modern  types  were  introduced 
or  became  predominant;  the  present  aspect  of  field  and  forest  com- 
mences, and  the  present  adjustment  of  the  relations  of  the  great  classes 
and  orders  was  established.  Then,  as  now,  the  rulers  of  the  seas  were 
great  sharks  and  whales ;  the  rulers  of  the  land,  mammalian  quadru- 
peds ;  and  the  rulers  of  the  air,  birds  and  bats.  Many  of  the  genera 
and  some  of  the  species  of  both  animals  and  plants  were  identical  with 
those  still  living.  The  dominant  class  becomes  now  Mammals :  Rep- 
tiles, therefore,  in  accordance  with  a  necessary  law,  decrease  in  size  and 
number,  and  thus  find  safety  in  a  subordinate  position.  In  some  of 
these  characteristics  of  the  Cenozoic  era  was  anticipated  in  the  Upper 
Cretaceous,  in  accordance  with  the  law  that  the  first  beginnings  of  each 
age  is  in  the  preceding  age. 

Divisions. — The  Cenozoic  era,  or  age  of  Mammals,  embraces  two 
periods,  viz. — 1.  The  Tertiary,  and  2.  The  Quaternary.  In  the  Ter- 
tiary all  the  mammals  are  now  wholly  extinct,  but  the  invertebrate 
species  are  some  of  them  still  living,  and  an  increasing  percentage  of 
living  species  appears  as  time  progresses.  In  the  Quaternary  most, 


502 


CJBNOZOIO  ERA— AGE  OF   MAMMALS. 


though  not  all,  of  the  mammalian  species  are  extinct,  but  nearly  all 
(ninety-five  or  more  per  cent)  of  the  invertebrate  species  are  living. 
These  facts  are  graphically  represented  in  the  following  diagram,  in 


CRETACEOUS 


T      £     R     T     I      A     R 


EOCENE 


MIOCENE       PLIOCENE 


QUATERNARY       RECENT 


G.LAC 


CHAM 


RECENT 


FIG.  842. — Diagram  illustrating  the  Relative  Duration  of  Lower  and  Higher  Species. 

which  the  curved  ascending  lines  are  the  lines  of  appearance  of  living 
species,  and  of  extinction  of  extinct  species  of  Foraminifera,  of  mol- 
luscous shells,  and  of  mammals.  In  each  case  the  lower  shaded  space 
represents  living  species  appearing  in  small  numbers,  and  increasing 
with  the  progress  of  time;  and  the  upper  unshaded  or  less  shaded 
space,  previous  species  gradually  dying  out  and  becoming  extinct.  It 
is  seen  that  living  species  of  Foraminifera  commenced  in  the  Creta- 
ceous, and  very  steadily  increased  in  number;  those  of  shells  com- 
menced in  the  earliest  Tertiary,  and  increased  somewhat  more  rapidly ; 
while  those  of  mammals  commenced  only  in  the  Quaternary,  and  in- 
creased correspondingly  rapidly.  Also  the  relative  proportion  of  living 
and  extinct  at  any  time  t  is  shown  by  comparing  the  amount  of  space 
above  and  below  the  line  at  that  time.  Also  the  relative  range  in  time 
of  low  and  high  species,  and  the  amount  of  overlapping  of  successive 
faunae,  are  shown. 

The  mammalian  class  probably  culminated  near  the  end  of  the  Ter- 
tiary or  during  the  Quaternary  period. 

SECTION  1. — TERTIARY  PERIOD. 

Subdivisions. — We  have  already  stated  that  the  general  differential 
characteristic  of  this  period,  as  compared  with  the  next,  is  that  all  the 
mammals,  and  most  of  the  invertebrates,  are  extinct ;  but  of  the  latter 
a  percentage,  small  at  first  but  increasing  with  the  progress  of  time, 
are  still  living.  It  is  upon  this  percentage  of  living  shells  that  Lyell 
has  based  his  division  of  the  Tertiary  period  into  three  epochs — a 

Lower,  Middle,  and  Upper  Tertiary,  or  Eocene,  Miocene,  and  Pliocene. 
•  • 

f  Pliocene  epoch,  or  Upper  Tertiary  =  50-90  per  cent  living  shells. 
Tertiary  period.  <  Miocene  epoch,  or  Middle  Tertiary  =  30  per  cent  living  shells. 
[  Eocene  epoch,  or  Lower  Tertiary  =  5-10  per  cent  living  shells. 


TERTIARY   PERIOD.  503 

These  percentages  are  expressed  graphically  in  the  diagram,  Fig. 
842.  In  these,  as  in  the  strata  of  all  periods,  however,  there  are  certain 
characteristic  species  by  which  the  epoch  may  be  known,  without 
counting  the  number  of  species  and  calculating  the  percentage  of  liv- 
ing. When  mammalian  species  are  found,  these  are  especially  charac- 
teristic of  the  epoch.  Again :  Although  Tertiary  mammalian  species 
are  all  extinct,  the  genera  and  families  are  not  all,  so  that  the  first 
appearance  of  living  families  and  genera  are  also  very  characteristic  of 
the  different  epochs. 

Rock-System—Area  in  the  United  States.— On  the  Atlantic  border, 
going  southward,  there  is  no  Tertiary,  except  a  small  patch  on  Martha's 
Vineyard,  off  the  coast  of  Massachusetts,  until  we  reach  New  Jersey. 
From  this  point  southward  the  Tertiary  is  a  broad  strip,  about  one 
hundred  miles  wide,  bordering  the  coast,  and  shown  on  the  map  (p.  291) 
by  the  space  shaded  with  oblique  lines  running  to  the  right.  It  con- 
stitutes the  low-countries  of  the  Southern  Atlantic  States.  At  its 
junction  with  the  metamorphic  region  of  the  up-countries,  there  are  in 
nearly  all  the  rivers  cascades  which  determine  the  head  of  navigation. 
Here,  therefore,  are  .situated  many  important  towns — e.  g.,  Richmond, 
Virginia ;  Raleigh,  North  Carolina ;  Columbia,  South  Carolina ;  Au- 
gusta, Milledgeville,  and  Macon,  Georgia.  This  has  been  called  the 
Fall-line.  The  same  strip  of  flat  lands  borders  also  the  Gulf,  expands, 
in  the  region  of  the  Mississippi  River,  northward  to  the  mouth  of  the 
Ohio,  and  then  continues  around  the  western  border  of  the  Gulf.  In 
the  Gulf-border  region,  however,  the  Tertiary  is  in  contact  below  with 
the  Cretaceous,  instead  of  with  Archaean,  as  on  the  Atlantic  border. 
This  whole  Atlantic-border  and  Gulf-border  Tertiary  is,  of  course,  a 
marine  deposit. 

In  the  interior,  on  the  Plains  and  in  the  Rocky  Mountain  region, 
there  are  enormous  areas  of  fresh-water  deposit,  some  Eocene,  some 
Miocene,  and  some  Pliocene,  which  are  of  extreme  interest. 

Among  the  Eocene  basins  the  most  remarkable  are  :  1.  The  Green 
River  basin.  2.  The  Uintah  basin.  Both  of  these  are  on  the  east  side 
of  the  Wahsatch  Mountains,  and  separated  from  each  other  by  the 
Uintah  Mountains,  one  being  north  and  the  other  south  of  that  range. 
They  were  possibly  once  united,  but  now  separated  by  erosion.  The 
strata  of  the  Green  River  basin  are  6,000  to  8,000  feet  thick. 

Among  the  Miocene  basins  the  most  interesting  are :  1.  The  Wliite 
River  basin,  in  Nebraska.  2.  The  John  Day  basin,  of  Oregon.  This 
latter  is  5,000  feet  thick,  but  is  largely  overlaid  by  the  great  lava-flood 
of  the  Northwest.  3.  Patches  of  Miocene  scattered  about  in  Nevada 
basin  region  show  that  deposits  of  this  age  cnce  extended  far  south  into 
Nevada  and  Eastern  California  (King). 

Of  Pliocene  basins :  1.  Niobrara  (or  Loup-fork)  basin,  occupying 


504 


CENOZOIC   ERA— AGE  OF  MAMMALS. 


partly  the  same  locality  as  the  Miocene  WJiite  River  basin,  but  more 
extensive,  reaching  southward  in  patches  almost  to  the  Gulf,  and  north- 
ward into  British  America.  2.  In  Oregon  also  there  is  a  Pliocene  basin, 
occupying  partly  the  same  region  as  the  previous  Miocene.  3.  Another 
discovered  by  Cope  in  the  basin  of  the  Rio  Grande.  4.  According  to 
King,  the  Oregon  and  Nevada  lake-deposit  was  in  Pliocene  times  greatly 
extended,  so  as  to  cover  the  whole  Basin  region,  but  has  been  largely 
removed  by  erosion  or  covered  by  Quaternary  deposits. 

All  these  deposits  are  imperfectly  lithified  sand  and  clays  in  nearly 
horizontal  position,  and  many  of  them  have  been  worn  by  erosive  agen- 
cies in  the  most  remarkable  way,  sometimes  into  knobs  and  buttes  like 
potato-hills  on  a  large  scale,  sometimes  into  castellated  and  pinnacled 
forms,  which  resemble  ruined  cities.  These  are  the  "  Mauvaises  Terres  " 
or  "  Bad  Lands  "  of  the  West  (Fig.  843). 


FIG.  843.—  Manvaises  Terres,  Bad  Lands  (after  Hayden). 

On  the  Pacific  coast,  a  large  portion  of  the  Coast  Ranges  from 
Southern  California  to  Washington  is  Tertiary,  as  are  also  in  many 
places  the  lowest  foot-hills  of  the  Sierras. 

Physical  Geography. — From  what  has  been  said  of  the  distribution 
of  the  rocks  of  this  age,  it  is  easy  to  reconstruct  in  a  general  way  the 
physical  geography  of  the  American  Continent  during  the  early  Ter- 
tiary period.  In  the  northern  part  the  Atlantic  shore-line  was  prob- 
ably leyond  the  present  line,  for  there  is  no  Tertiary  deposit  visible 
there.  The  shore-line  of  that  time  crossed  the  present  shore-line  in 
New  Jersey,  then  passed  along  the  line  of  junction  of  the  Tertiary  with 
the  Metamorphic,  its  waves  washing  primary  shores  all  along  the  At- 
lantic coasts,  as  it  does  now  in  the  northern  portion  only ;  then  along 


TERTIARY   PERIOD. 


505 


the  junction  of  the  same  with  the  Cretaceous.  The  whole  low-coun- 
tries of  the  Southern  Atlantic  States  and  the  whole  of  Florida  were  then 
a  sea-bottom.  The  Gulf  of  Mexico  was  far  more  extensive  than  now, 
and  especially  it  sent  a  wide  bay  northward  to  the  mouth  of  the  Ohio- 
The  Mississippi  Eiver  below  that  point  did  not  then  exist.  The  Ohio, 
Arkansas,  and  Red  Rivers  emptied  by  separate  mouths  into  the  embay- 
ment  of  the  Gulf. 

This  was  at  the  beginning.  During  the  course  of  the  Tertiary  the 
shore-line  was  gradually  transferred  eastward  along  the  Atlantic,  and 
southward  along  the  Gulf,  as  shown  by  the  dotted  lines  introduced  in 
the  Tertiary  areas  in  the  map  on  page  291. 

In  the  interior,  in  the  region  of  the  Plains,  the  Plateau,  and  the 
Basin,  there  were  at  different  times  immense  fresh-iuater  lakes.  The 
places  of  some  of  these  are  indicated  on  map,  Fig.  844,  in  dotted  out- 


Fio.  844.— Map  of  Tertiary  Times,  showing  Outline  of  Coast  and  Places  of  Principal  Tertiary  Lakes. 

line.  These  outlines,  however,  are  not  intended  to  be  accurate.  These 
lakes  drained  some  of  them  into  the  Mississippi,  some  into  the  Colo- 
rado, and  some  into  the  Columbia  River. 

The  Pacific  shore-line  at  that  time  was  along  the  foot-hills  of  the 
Sierra  Range,  and  therefore  the  whole  region  occupied  by  the  Coast 
Ranges  and  the  Sacramento  and  San  Joaquin  Valleys,  and  also  portions 
of  Western  Oregon,  were  then  a  sea-bottom.  These  facts  are  roughly 
represented  on  map,  Fig.  844.  The  positions  of  the  principal  mount- 
ain-chains, e.  g.,  Sierra,  Wahsatch,  Uintah,  the  eastern  border  of  the 


506  CENOZOIC   EKA— AGE   OF  MAMMALS. 

Rocky  Mountains,  and  Appalachian,  are  represented,  in  order  the  better 
to  locate  the  lakes.  It  will  be  observed  that  the  continent  is  nearly 
finished. 

Europe  is  now  remarkable  for  its  inland  seas.  It  was  much  more 
so  in  Tertiary  times.  Many  great  cities,  as,  for  example,  London,  Paris, 
Vienna,  are  situated  on  Tertiary  strata,  partly  because  these  strata  are 
usually  found  on  the  borders  of  continents,  and  partly  because  they 
are  often  found  in  the  course  of  great  rivers,  which  once  drained  lake- 
basins. 

Character  of  the  Rocks. — The  rocks  of  this  period,  along  the  At- 
lantic border  and  in  the  interior  Plains  and  Rocky  Mountain  region, 
are  mostly  imperfectly  lithified ;  but  on  the  Pacific  coast  they  are  not 
only  of  stony  hardness,  but  in  many  cases  completely  metamorpJiic. 
Much  of  the  rock  in  the  Coast  Chain  is  scarcely  distinguishable  from 
the  schists  of  the  Palaeozoic  or  still  older  periods.  The  reason  is  evi- 
dent— metamorphism  is  closely  connected  with  mountain-making,  and 
mountain-making  continued  until  the  Tertiary  on  the  Pacific  coast. 

Goal, — Again,  in  the  Tertiary  rocks  we  find  coal,  although  more 
usually  in  the  imperfect  condition  called  lignite.  We  have  already  stated 
that  the  Rocky  Mountain  coal-fields  are  by  some  referred  to  the  Ter- 
tiary. We  have  referred  these  to  the  Laramie.  But  there  are  others 
about  which  there  is  as  yet  no  controversy.  The  Coos  Bay  coal,  of 
Oregon,  is  probably  Miocene-Tertiary.  The  Nevada  coal  is  Upper  Eo- 
cene or  Lower  Miocene.  Again,  Mr.  Selwyn,  the  Geologist  of  Canada, 
has  reported  large  fields  of  coal  on  the  Qu'Appelle  and  the  North 
Saskatchewan  Rivers,  covering  an  area  of  25,000  square  miles,  a  part, 
at  least,  of  which  he  refers  to  the  Tertiary.  Much  of  this  coal  is  of 
good  quality.  It  seems  most  probable,  however,  that  this  also  belongs 
mostly  to  the  Laramie. 

In  Europe  also-  an  imperfect  coal  (lignite)  is  found  in  the  Miocene 
in  considerable  quantity. 

Lava-fields. — The  great  lava-fields  of  the  western  part  of  the  con- 
tinent belong  mostly  to  the  Tertiary :  (1.)  The  great  Lava-flood  of 
the  Northwest  (already  spoken  of  Oil  p.  210),  which  covers  Northern 
California,  Northwestern  Nevada,  a  large  part  of  Oregon,  Washington, 
and  Idaho,  and  extends  far  into  Montana  and  British  Columbia.  This 
is  one  of  the  largest  fields  in  the  world.  (2.)  The  lava- field  of  the 
Coast  Range  of  California,  especially  in  Napa  and  Lake  Counties,  and 
northward  into  Oregon.  (3.)  Enormous  fields  in  the  Plateau  and 
Basin  regions. 

Life- System. 

General  Remarks. — We  have  already  spoken  of  the  great  and  rapid 
change  in  the  life-system  between  the  Cretaceous  and  the  Tertiary, 
even  where  the  two  series  of  rocks  are  continuous  and  conformable. 


TERTIARY  PLANTS.  507 

This  indicates,  undoubtedly,  a  more  rapid  rate  of  evolution  at  that  time. 
But  it  also  indicates,  as  one  cause  of  this  rapid  evolution,  a  migration 
of  species  brought  about  by  changes  in  physical  geography  and  climate, 
and  the  imposition  of  one  fauna  and  flora  upon*  another,  and  the  ex- 
termination or  else  modification  of  one  by  the  other.  It  is  difficult  to 
conceive  of  these  sudden  changes  taking  place  otherwise.  We  shall 
speak  more  fully  of  this  important  point  under  the  Quaternary. 

The  general  character  of  the  life-system  of  the  Tertiary,  as  already 
said,  was  in  the  main  similar  to  the  present.  Nearly  all  the  genera  and 
many  of  the  species  of  plants  and  invertebrate  animals  were  the  same 
as  now,  and  the  difference  in  aspect  would  hardly  be  recognized  by  the 
popular  eye ;  it  was  certainly  not  greater  than  now  exists  between  dif- 
ferent countries.  It  is  only  among  Mammals  that  the  difference  was 
very  conspicuous. 

Plants. 

Among  plants,  nearly  all  the  genera  of  Dicotyls,  Palms,  and  Grasses, 
were  the  same  as  noiv,  though  most  of  the  sjwcies  are  extinct.  TJie gen- 
era were  the  same  as  now,  but  not  in  the  same  localities.  On  the  con- 
trary, the  vegetation  indicated  a  much  warmer  climate  than  exists  now 
in  the  same  localities.  For  example,  if  we  regard  the  Lignitic  as 
Eocene- Tertiary,  instead  of  Cretaceous,  as  do  paleontological  botanists 
generally,  then  of  more  than  300  species  of  plants  found,  a  very  large 
proportion  were  Palms,  and  many  of  them  of  great  size ;  and  among  the 
Dicotyls  many,  like  Magnolias,  indicated  a  warm  climate.  Lesquereux 
thinks  the  climate  of  Fort  Union  was  then  similar  to  that  of  Florida 
and  Lower  Louisiana  now.  There  has  been  a  southward  migration 
of  forms  since  that  time.  Again,  in  Eocene  times  there  were  fifteen 
species  of  Palms  in  Europe ;  and  in  the  Tyrol  the  flora,  according  to 
Von  Ettingshausen,  indicated  a  temperature  of  74°  to  81°  Fahr.,  and 
many  of  the  plants  are  Australian  in  type.  In  the  Pliocene,  on  the 
contrary,  many  European  plants  were  like  those  in  America  at  the 
present  time. 

During  the  Miocene,  Europe  was  covered  with  evergreens  such  as 
could  grow  now  only  in  the  southernmost  part ;  and  that  even  as  far  as 
Lapland,  and  Iceland,  and  Spitzbergen.  It  has  been  estimated  that  the 
Miocene  flora  indicates  a  mean  temperature  of  12°  to  15°  higher  than 
now  exists  in  Middle  Europe.  In  America,  during  the  same  epoch, 
Sequoias  almost  identical  with  the  Big  Tree  and  Redwood  of  Califor- 
nia ;  and  Libocedrus,  one  of  them  identical  with  the  L.  decurrens  of 
California ;  and  Magnolias  similar  to  the  M.  grandiflora  of  the  South- 
ern Atlantic  States ;  and  Taxodium  distichum,  the  cypress  of  the 
swamps  of  Carolina  and  Louisiana,  all  existed  in  Greenland,  and  most 
of  them  also  in  Northern  Europe,  and  Iceland,  and  Spitzbergen,  and 
even  Grinnell  land  81°  north  latitude.  Heer  estimates  the  temperature 


508 


CENOZOIC  ERA— AGE  OF  MAMMALS. 


of  Greenland  in  the  Miocene  as  30°  higher  than  now.  Evidently  there 
was  no  polar  ice-cap  at  that  time. 

It  is  interesting  to  note  again  remnants  of  former  types  of  vegeta- 
tion now  almost  extinct.  According  to  Heer,  there  are  twenty-four 
extinct  species  of  Sequoias  known — ten  in  Cretaceous,  and  fourteen  in 
the  Tertiary.  To  these  must  now  be  added,  four  or  five  species  from 
the  Potomac  formation  (Fontaine).  Only  two  remain,  and  these  only 
in  isolated  patches  in  California. 

These  facts  show  not  only  a  warm  but  a  uniform  climate,  and  prob- 
ably also  a  connection  in  high  latitudes  between  the  American  and  Eu- 
ropean Continents.  A  similar  connection,  shown  also  by  the  vegeta- 


FIG.  852. 

FIGS.  845-852.— AMERICAN  TERTIARY  PLANTS  (after  Safford  and  Lesquereux):  845.  Cinnamomum 
Mississippiense.  846.  Quercus  crassinervis.  847.  Andromeda  vaccinifoliae  affinie.  848.  Carpo- 
hthes  irregularis.  849.  Fagus  ferruginea— Nut.  850.  Fruit  of  Sequoia  Langsdorfii  (after  Heer). 
851.  Leaf  of  Sequoia  Langsdorfli  (after  Heer).  852.  Quercus  Saffordi. 

tion,  probably  existed  between  Alaska  and  the  Asiatic  Continent  at  that 
time.  The  accompanying  figures  represent  some  of  the  Dicotyls  and 
Monocotyls  of  American  and  European  Tertiary. 


TERTIARY   PLANTS. 


509 


FIG.  857. 


FIG.  858. 


FIGS.  853-859.— PLANTS  OP  EUROPEAN  TERTIARY:  853.  Chamserops  Helvetica.  854.  Sabal  major. 
855.  Platanusaceroides:  a,  Leaf;  6,  Core  of  a  Cluster  of  Fruits;  c,  Single  Fruit.  856.  Cinnamo- 
mum  polymorphum:  a,  Leaf;  b.  Flower.  857.  Acer  trilobatum:  a,  Leaf;  6,  Flower;  c,  Seed. 
858.  Podogonium  Knorrii.  859.  Liquidambar  Europeum,  from  (Eningen:  a,  Leaf;  b,  Fruit  (after 
Heer). 

Another  conclusion  to  be  drawn  from  the  foregoing  facts  is  that,  in 
the  race  of  evolution,  Europe  seems  to  have  distanced  most  other  coun- 


510 


CENOZOIC   ERA— AGE   OF  MAMMALS. 


tries.  The  Australian  flora  is  now  only  where  the  European  flora  was 
in  Eocene  times,  and  the  American  flora  now  where  the  European  was 
in  the  Pliocene.  The  probable  reason  is  that,  in  Europe,  in  these  later 
geological  times,*  changes  of  physical  geography  and  climate,  and  con- 
sequent migrations  of  species,  were  more  frequent,  and  the  struggle  for 
life  more  severe.  Australia  especially,  probably  on  account  of  its  isola- 
tion, has  advanced  more  slowly  than  most  other  countries.  Many  rem- 
nants of  extinct  faunas  and  floras  exist  there  still. 

Still  another  conclusion  is,  that  the  floras  of  Europe,  America,  and 
Australia,  were  far  less  differentiated  from  one  another  then  than  now. 

Diatoms. — If  the  highest  of  plants — Dicotyls  and  Monocotyls — were 
abundant,  probably  more  abundant  than  now,  so  also  were  the  lowest 
order  of  uni-celled  plants — the  Diatoms.  Immense  deposits,  consisting 
wholly  of  the  siliceous  shells  of  these  microscopic  plants,  are  found  in 
the  Tertiary.  In  Europe  the  Bohemian  deposit  is  celebrated.  It  is 


FIG.  860.— Microscopic  View  of  Richmond  Infusorial  Earth  (by  Ehrenberg). 

fourteen  feet  thick,  and  every  cubic  inch  of  the  material,  according  to 
Ehrenberg,  contains  40,000,000,000  shells.  The  Richmond  (Virginia) 
deposit  is  equally  well  known.  It  is  thirty  feet  thick,  and  many  miles 

*  In  Cretaceous  times  the  flora  of  America  seems  to  have  been  more  advanced  than 
that  of  Europe. 


TERTIARY   AXIMALS. 


511 


in  extent.  Similar  deposits  are  especially  abundant  in  California. 
They  are  found  in  at  least  a  dozen  localities  where  the  Tertiary  rocks 
prevail,  as,  for  example,  at  San  Pablo,  in  Shasta  County,  and  near 
Monterey,  the  last  deposit  being  fifty  feet  thick. 

Some  of  the  more  remarkable  forms  of  Diatoms  are  shown  in  Fig. 
800,  which  is  a  view  under  the  microscope  of  the  Richmond  deposit. 

Deposits  of  this  kind  are  usually  called  infusorial  earths.  They  may 
often  be  recognized,  even  without  microscopic  examination,  by  their  soft, 
chalky  consistence,  their  insolubility  in  acids,and  their  extreme  lightness. 

Origin  of  Infusorial  Earths. — It  is  well  known  that  mud  composed 
of  diatom  shells  accumulates  at  the  bottoms  of  ponds,  and  lakes,  and 
sluggish  streams.  In  the  deepest  parts  of  Lake  Tahoe,  where  sedi- 
ments do  not  reach,  the  ooze  is  composed  wholly  of  infusorial  shells. 
It  has  been  shown,  also,  by  Dr.  Blake,*  that  the  deposits  from  hot 
springs  of  California  and  Nevada,  even  where  the  temperature  is  163° 
to  174°,  abound  in  Diatoms  of  the  same  species  as  those  found  in  Cali- 
fornia infusorial  earths.  It  is  probable,  therefore,  that  many  of  these 
deposits  were  made  in  hot  springs  and  hot  lakes,  which,  judging  from 
the  volcanic  activity  of  that  time,  abounded  in  California,  then  even 
far  more  than  now.  Dr.  Blake  thinks  the  infusorial  earths  of  Cali- 
fornia are  Miocene.  In  the  hot-springs  of  Yellowstone  Park  deposits 
of  this  kind  are  now  forming  over  many  square  miles  and  are  five  or 
six  feet  thick  (page  1G1). 

Animals. 

As  already  stated,  among  Invertebrates  there  was  a  general  similarity 
to  the  present  fauna.  Nearly  all  the  genera  and  many  of  the  species, 
were  identical  with  those  still  living.  The  relation  between  the  various 
orders  which  prevail 
now,  commenced 
then.  The  present 
basis  of  adjustment 
was  then  established. 
Then,  as  now,  Brachi- 
opods  and  Crinoids 
were  nearly  all  gone,  FI«.  sei.-Nnmmuima  isevigata. 

Echinoderms      were 

nearly  all  free,  and  Bivalves  were  nearly  all  Lamellibranchs.  Then,  as 
now,  naked  Cephalopods  and  short-tailed  Crustaceans  greatly  predomi- 
nated. A  glance  at  the  following  figures  of  Tertiary  shells  (Figs.  862- 
876)  will  show  the  general  resemblance  to  those  of  the  present  seas. 

In  regard  to  the  Invertebrates,  there  are  only  three  or  four  points  of 
sufficient  importance  to  arrest  our  attention  in  a  rapid  survey. 


*  American  Journal  of  Science,  Part  III,  vol.  iv,  p.  148. 


512 


CEXOZOIC   ERA— AGE   OF   MAMMALS. 


Among  RMzopods,  Nummulites  (a  foraminifer,  Fig.  861)  abounded 
to  an  extraordinary  degree.  Eocene  strata,  many  thousand  feet  thick, 
are  formed  of  these  shells.  The  Nummulitic  limestone  of  the  Alps 
extends  eastward  to  the  Carpathians,  westward  to  the  Pyrenees,  and 
southward  into  Africa.  It  was  largely  quarried  to  build  the  Pyramids 


FIG.  867.  FIG.  868.  FIG.  869. 

FIGS.  862^869.— EOCENE  TERTIARY  SHELLS  :  862.  Oetrea  eellajformis  (after  Meek).  863.  Ostrea 
Georgiana  (after  Meek).  864.  Pecten  nuperum  (after  Wailes).  865.  Anornalocardia  Missis- 
sippiensis  (after  Conrad).  866.  Umbrella  planulata  (after  Wailes).  867.  Turritella  alveata 
(after  Wailes).  868.  Volutalithes  dumosa  (after  Wailes).  869.  Volutalithes  symmetrica  (after 


of  Egypt 
layas. 


It  occurs  also  extensively  in  Asia  Minor  and  in  the  Hima- 


TERTIARY  ANIMALS. 


513 


This  limestone  occurs  in  the  Alps  10,000  feet,  in  the  Pyrenees 
11,000  feet,  and  in  the  Himalayas  15,000  and  even  19,000  feet  above 


FIG.  874.  FIG.  675.  FIG.  876. 

FIGS.  870-876.— CALIFORNIA  MIOCENE  SHELLS  (after  Gabb):  870.  Ostrea  Titan,  x  $.  871.  Pecten 
Cerrocensis,  x  1.  872.  Venus  pertenuis.  873.  Cardium  Meekianum.  674.  Cancellaria  vetusta. 
875.  Ficus  pyriformis.  876.  Echinorachnis  Brewerianus. 

the  sea-level.     We  see,  then,  the  immense  changes  which  have  occurred 
by  mountain-making  since  the  Eocene. 
S3 

sf*~^ 

0V  THB 


514: 


CENOZOIC  ERA— AGE   OF  MAMMALS. 


Among  bivalve  shells,  common  forms  of  the  present  day,  such  as 
the  oyster,  the  clam  ( Venus),  the  scallop-shell  (Pecten),  etc.,  were  very 
numerous,  and  some  of  very  large  size.  Oysters  especially  seemed  to 
have  reached  their  maximum  development  in  the  Tertiary.  The  Ostrea 
Georgiana  (Fig.  863)  was  ten  inches  long  and  four  wide ;  the  Ostrea 
Caroliniensis  was  of  equal  size,  but  shorter  and  broader.  A  specimen  of 
the  Ostrea  Titan  of  California  and  Oregon  now  lies  before  us,  which  by 
measurement  is  thirteen  inches  long,  eight  wide,  and  six  thick  (Fig. 
870),  and  a  specimen  of  Pecten  Cerrocensis  of  California,  nine  inches 
across  (Fig.  871).  Among  univalves  also  nearly  all  the  forms  are 
familiar.  The  illustrations  are  taken  from  the  Eocene  and  Miocene. 
The  Pliocene  shells  are  almost  undistinguishable  from  living  shells, 
except  by  the  practiced  eye.  It  seems  useless  to  give  them  in  an  ele- 
mentary work. 

Insects. — There  are  several  interesting  points  connected  with  this 
class  which  must  not  be  omitted.  We  have  usually  found  insects  abun- 
dant in  connection  with  luxuriant  vegetation.  During  the  Miocene, 
phenogamous  vegetation  was  even  more  abundant  than  now ;  there  was 
also  extreme  fullness  of  insect-life.  All  orders,  even  the  highest,  viz., 
Lepidoptera  (butterflies — Fig.  878)  and  Hymenoptera  (bees,  ants,  etc. 
— Fig.  877),  were  represented. 


FIG.  877.— INSECTS  OP  EUROPEAN  MIOCENE  (after  Heer):  a,  Apis  Adamitica;  b,  Ponera  veneraria 
male,  b'  female;  c,  Vespa  atavina;  d,  d,  Ammophila  inferna;  e.  Imhoffia  pallida;  /,/',/".  For- 
mica lignitum— female,  male,  and  worker;  g,  Myrmica  tertiaria;  h,  Ichneumon  infernalis;  i, 
Xilocopa  senilis;  k,  Bombus  Jurinei;  I,  Scalea  saussureana. 

In  the  Miocene  of  Europe,  1,550  species  of  insects  have  been  found  ; 
and  of  these  more  than  900  species  at  (Eningen  in  a  stratum  only  a  few 
feet  thick  (Lyell).  In  places  the  stratum  is  black  with  the  remains  of 
The  same  stratum  is  also  full  of  leaves  of  Dicotyls,  of  which 


TERTIARY    ANIMALS. 


515 


FIG.  878.— Vanessa  Pluto. 


Heer  has  described  500  species.     Mammalian  remains  and  fishes  are 
also  found  in  them. 

It  is  interesting  to  inquire  into  the  conditions  under  which  these 
strata  were  formed  and  filled  with  these  remains.  On  Lake  Superior, 
at  Eagle  Harbor,  in  the 
summer  of  1844,  we 
saw  the  white  sands  of 
the  beach  blackened 
with  the  bodies  of  in- 
sects of  many  species, 
but  mostly  beetles  cast 
ashore.  As  many  spe- 
cies were  here  collected 
in  a  few  days,  by  Dr. 
J.  L.  Le  Conte,  as  could 
have  been  collected  in 
as  many  months  in  any  other  place.  The  insects  seem  to  have  flown 
over  the  surface  of  the  lake ;  to  have  been  beaten  down  by  winds  and 
drowned,  and  then  slowly  carried  shoreward  and  accumulated  in  this 
harbor,  and  finally  cast  ashore  by  winds  and  waves.  Doubtless,  at 
(Eningen,  in  Miocene  times,  there  was  an  extensive  lake  surrounded  by 
dense  forests ;  and  the  insects  drowned  in  its  waters,  and  the  leaves 
strewed  by  winds  on  its  surface,  were  cast  ashore  by  its  waves.  Heer 
believes  also  that  carbonic-acid  emissions  helped  to  destroy,  and  de- 
posits of  carbonate  of  lime  to  preserve,  the  insects.  Over  five  hundred 
of  the  (Eningen  insects  were  beetles. 

Among  the  insects  found  at  (Eningen,  Switzerland,  and  Radoboj, 
Croatia,  are  a  great  many  ants  (Fig.  877).  In  all  Europe  there  are 
now  about  fifty  species  of  ants.  Heer  found  in  the  Miocene  of  (Enin- 
gen and  Radoboj  more  than  100  species*  And,  what  is  very  remark- 
able, nearly  all  are  winged  ants.  Ants  of  the  present  day  are  male, 
female,  and  neuter.  The  males  are  winged  throughout  life,  and  never 
live  in  the  nests,  but  soon  perish.  The  females  are  also  winged  until 
they  are  fertilized  ;  then  they  drop  their  wings  and  live  in  communi- 
ties in  a  wingless  condition  ever  afterward.  The  neuters  are  always 
wingless,  and  therefore  always  live  in  nests  or  in  communities.  It  is 
probable  that  ants  at  first  were  only  winged  males  and  females,  living 
in  the  open  air  like  other  insects.  The  wingless  condition  and  the  neu- 
tral condition  are  both  connected  with  their  peculiar  social  habits  and 
instincts,  and  have  been  gradually  developed  along  with  the  develop- 
ment of  their  habits  and  instincts.  It  is  probable  that  all  these  remark- 
able peculiarities,  viz.,  the  wingless  condition,  the  neutral  condition,  the 


Pouchct,  Popular  Science  Monthly,  June,  1873. 


516 


CENOZOIC  EKA— AGE   OF  MAMMALS. 


wonderful  instincts,  and  organized  social  habits,  have  been  developed 
together  since  the  introduction  of  this  order  in  Early  Tertiary. 

In  the  fresh- water  Miocene  of  Auvergne,  France,  there  is  a  remark- 
able stratum  called  indusial  limestone^  because  it  is  largely  composed 
of  the  cast-off  hollow  cases  (indusia)  of  the  caddis- worm  or  larva  of  the 
caddis-fly  (Phryganea),  cemented  together  by  carbonate  of  lime.  The 
number  of  these  cases  is  countless.  The  caddis-worm  of  the  present 
day  forms  for  itself  a  hollow  cylindrical  case,  of  bits  of  stick  or  pieces 
of  shell,  or  sometimes  of  whole  small  shells,  binding  these  together  by 
means  of  a  kind  of  web.  In  this  hollow  cylinder  it  lives,  only  putting 
out  the  head  and  two  or  three  first  joints  of  the  body,  to  which  the 
feet  are  attached,  in  walking.  When  they  complete  their  metamor- 
phoses, they  leave 
their  cases.  Fig. 
881  is  a  recent  cad- 
dis-worm with  its 
case  of  small  shells 
stuck  together ; 
Fig.  880  are  indu- 
sia of  the  Miocene 
caddis-worm  ;  and 
Fig.  879  is  the 
limestone  in  place, 
a  being  the  indusial 
layer. 

In  Auvergne,  in 
Miocene  times, 
there  existed  a  shal- 
low lake,  in  which 
carbonate  of  lime 
was  depositing,  as 
in  many  lakes  of 
the  present  day.  In 
this  lake  lived  myr- 
iads of  caddis- 
worms,  and  their 
indusia  accumula- 
ted for  countless 
generations. 

In  the  Tertiary 

strata,  about  the  shores  of  the  Baltic,  and  also  in  Sicily,  in  Asia  Minor, 
and  several  other  localities  usually  associated  with  lignite,  are  found 
masses  of  amber.  This  substance  is  a  fossil  resin  of  several  species  of 
Conifer,  especially  Pinites  succinifer.  It  is  often  quite  transparent, 


FIG.  880. 


FIG.  881. 


FIGS.  879-881.— 879.  Indusial  Limestone  interstratified  with  Fresh- 
Water  Marls.  880.  A  Portion  (natural  size)  showing  the  Phry- 
ganea  Cases.  881.  Recent  Larva  of  a  Phryganea,  with  its  Case. 


TERTIARY  ANIMALS. 


517 


and  inclosed  within  may  be  seen  perfectly  preserved  insects  of  many 
kinds.  Over  800  species  of  insects,  and  fragments,  of  many  species 
of  plants  have  been 
found  thus  inclosed. 
The  degree  of  pre- 
servation is  marvel- 
ous; even  the  most 
delicate  parts,  the 
slender  legs,  the 
jointed  antenna?,  and 
the  gauzy  wings  are 
perfect.  The  manner 
in  which  these  insects 
were  entangled,  in- 
closed, and  preserved, 
may  be  easily  observed 


FIG.  882.— Prodryas  Persephone  (after  Scudder). 


even  at  the  present 
day.  The  gum  issu- 
ing from  Conifers  is  at  first  in  the  form  of  semi-liquid,  transparent 
tears.  Flies,  gnats,  etc.,  alighting  on  these,  stick  fast,  and  by  the  run- 
ning down  of  further  exudations  are  enveloped  and  preserved  forever. 
The  legs,  both  in  the  modern  and  the  fossil  resin,  are  often  found 
broken  by  the  struggles  of  the  insects  to  extricate  themselves.  The  in- 
sects of  the  Tertiary,  like  the  plants,  show  a  decided  tropical  character. 
But  probably  the  ,richest  beds  in  insects  yet  found  are  at  Florissant, 
Colorado.  Here  fresh-water  shales  of  Green  River  age  are  black  with 

remains  of  insects  of  all  orders  now  existing. 
According  to  Scudder,*  about  1,000  species 
are  recognizable,  besides  many  plants,  sev- 
eral fishes,  and  a  bird  with  feathers  pre- 
served. Of  30,000  specimens  of  insects  in 
all  museums,  about  one  half  are  from  this 
locality.  Here,  also,  as  in  Europe,  Hymen- 
opters  and  Coleopters  are  most  abundant, 
and  all  the  species  indicate  tropical  climate. 
Among  the  insects  found  here  are  seven 
species  of  butterflies  (only  nine  species  are 
known  from  all  the  rest  of  the  world).  A  beautifully  preserved  speci- 
men is  shown  in  Fig.  882.  At  Florissant,  in  Eocene  times,  there  was 
a  lake,  and  insects  were  cast  ashore  and  accumulated  in  the  manner 
already  described.  Other  Tertiary  lake-deposits  in  the  West  are  also 
rich  in  insects  (Fig.  883). 


Fro.  883.— Sackenia  nrcnata,  from 
Tertiary  of  Utah  (after  Scudder). 


*  Bulletin  of  the  United  States  Geological  Survey,  vol.  vi,  No.  2. 


518 


CENOZOIC   ERA— AGE   OF  MAMMALS. 


Fishes. — The  present  relation  between  the  three  great  orders  of 
Fishes — Teleosts, .  Ganoids,  and  Placoids — was  first  fairly  established  in 
the  Tertiary.  Teleosts  were  first  introduced  in  the  Creta- 
ceous, but  only  in  the  Tertiary  did  they  become  very 
abundant.  Ganoids,  on  the  contrary,  became  fewer  in 
number ;  they  sank  into  their  present  subordinate  position. 
Among  Placoids,  the  Hybodonts  are  gone,  the  Cestra- 
cionts  are  few  in  number,  but  the  Squalodonts  reach  their 


FIG.  884. 


FIG.  888. 

FIGS.  884-888.— TERTIARY  FISHES— Placoids :  884.  Lamna  elegans  (after  Agassiz).  885.  Notidanus 
primigeuius  (after  Agassiz).  886.  Carcharodon  augustidens  (after  Gibbes).  887.  Carcharodon 
megalodon,  x  £  (after  Gibbes).  Teleost;  888.  Clupea  alta  (after  Leidy). 

maximum  development,  both  in  number  and  size.  In  the  marine  Ter- 
tiary of  the  Atlantic  border,  both  Eocene  and  Miocene,  sharks'  teeth 
are  found  in  immense  numbers,  and  of  very  great  size.  Some  of  the 
triangular  teeth  of  the  Carcharodon  megalodon  (Fig.  887)  are  found 
six  and  a  half  inches  long  and  six  inches  broad  at  the  base.  The  own- 


TERTIARY   ANIMALS. 


519 


ere  of  such  teeth  must  have  been  fifty  to  seventy  feet  long.     Some  of 
the  more  common  forms  of  sharks'  teeth  of  the  American  Tertiary, 


FIGS.  889,  890.— TERTIARY  FISHES—  Teleosts :  889.  Rhombus  minimus,  Lower  Eocene.    890.  Lcbias 

cephalotes,  Miocene. 

and  Teleosts  from  American  and  European  Tertiary,  are  given  in  the 
preceding  figures. 

Reptiles. — The  age  of  Reptiles  is  past.  The  huge  Enaliosaurs,  Dino- 
saurs, Mosasaurs,  and  Pterosaurs,  are  all  extinct.  Their  class  is  now 
represented  by  Crocodiles,  Lizards,  Turtles,  Snakes,  and  Frogs,  though 
their  place  as  rulers  is  supplied  by  Mammals  and  Birds.  Five  species 
of  Snakes,  some  of  them  eight  feet  long,  and  nine  Crocodilians,  have 
been  found  in  the  Eocene  of  Wyoming,  and  several  also  in  Europe. 
In  the  Miocene  of  Europe  at  CEningen,  a  Salamandroid  Amphibian 
was  found  and  described  in  1728  by  Scheuchzer,  a  physician  and  natu- 
ralist, professor  in  the  University  of  Altorf.  He  gave  it  the  title 
"  Homo  Diluvii  Testis"  believing  it  to  be  the  skeleton  of  a  human  being 


520 


CENOZOIC  ERA— AGE  OF  MAMMALS. 


destroyed  by  the  deluge.  The  length  was  about  four  feet.  It  was  re- 
served for  Cuvier  to  show  that  the  fossil  was  not  human,  though  the 
name  Andrias  Scheuchzeri  (Fig.  891)  had  become  permanently  at- 
tached to  it  through  Scheuchzer's  mistake.  A 
living  species  of  the  same  genus  is  now  found  in 
Japan,  and  is  of  gigantic  size.  A  representation 
of  it  is  given  in  Fig.  892,  for  comparison  with  its 
fossil  precursor.  The  Miocene  of  the  Himalayas 
furnishes  a  gigantic  turtle  (Colossochelys  Atlas], 
the  carapace  of  which  was  twelve  feet  long  and 
eight  feet  wide,  and  seven  feet  high  in  the  roof, 
and  the  whole  animal  was  probably  twenty  feet 
long.  Over  sixty  species  of 
Tertiary  turtles,  and  eight- 
een or  twenty  species  of 
crocodiles,  have  been  de- 
scribed from  foreign  coun- 
tries (Dana). 

¥"**  ft'l  /;*'^(r''/7"''  rriie    ^roco(lilians>    tne 

*   »j  &*$* ''*'*•)  highest  living  order  of  rep- 

tiles, first  appeared  in  the 
Triassic,  but  only  in  gener- 
alized forms — Stagonolepis, 
Belodon,  etc. — which  close- 
ly connected  them  with  the 
Lizards.  From  this  early 
form  Huxley  has  traced 
with  consummate  skill  the 
gradual  differentiation  of 
this  order,  in  the  position 
of  the  posterior  nares,  the  structure  of  the  head  and  the  form  of  the 
vertebral  bodies,  step  by  step  through  the  Jurassic,  Cretaceous,  to  the 
Tertiary,  where  the  type  reached  its  perfection. 

Birds. — The  class  of  Birds  in  the  Cretaceous  was  represented  only 
by  the  reptilian  birds  and  ordinary  water  birds.  Now,  in  the  Tertiary, 
however,  the  reptilian  birds — vertebrated-tailed  and  socket-toothed — 
have  disappeared.  The  bird-class  is  fairly  differentiated  from  the  rep- 
tilian class,  and  the  connecting  links  destroyed.  Birds  of  all  kinds  now 
appear — land-birds  as  well  as  water-birds.  In  America,  among  land- 
birds,  woodpeckers,  owls,  eagles,  etc.,  have  been  discovered  and  de- 
scribed by  Marsh.  The  number  of  species  found  in  Europe  is  much 
greater  than  in  America.  The  Miocene  beds  of  Central  France  alone 
have,  according  to  Milne-Edwards,  afforded  seventy  species.  The  Mio- 
cene birds,  like  the  plants  and  insects,  show  a  decided  tropical  charac- 


FIG.  891. 

FIGS.  891,  892.— 891 
Switzerland 


FIG.  892. 

Andrias    Scheuchzeri,  Miocene  of 
(after  Heer).    892.  Andrias  Japonic 


a,  a  living  Salamander  from  Japan,  x  ^  (after  Heer.) 


TERTIARY   ANIMALS. 


521 


ter.  "  Parrots  and  Trogons  inhabited  the  woods ;  Swallows  built,  in 
the  fissures  of  the  rocks,  nests  in  all  probability  like  those  now  found 
in  certain  parts  of  Asia  and  the  Indian  Archipelago ;  a  Secretary-bird, 
nearly  allied  to  that  of  the  Cape  of  Good  Hope,  sought  in  the  plains  the 
serpents  and  reptiles  which  at  that  time, 
as  now,  must  have  Jurnished  its  nourish- 
ment. Large  Adjutants,  Cranes,  Flamin- 
goes, Palaeolodi  (birds  of  curious  forms 
intermediate  between  Flamingoes  and  or- 
dinary Grails),  and  Ibises,  frequented  the 
margins  of  the  water  where  insect-larva3 
and  mollusks  abounded.  Pelicans  floated 
on  the  lakes  ;  and,  lastly,  Sand-grouse  and 
numerous  Gallinaceous  birds  assisted  in 
giving  to  this  ornithological  population  a 
strange  physiognomy  which  recalls  to 
mind  the  descriptions  given  by  Living- 
stone of  certain  lakes  in  Southern  Af- 
rica." 

But  although  the  class  of  birds  was 
already  well  differentiated,  yet  some  rem- 
nants of  generalized  forms  still  remained. 
A  toothed-bird  has  been  found  in  the 
London  clay  (Eocene),  and  named  by 
Owen  Odoniopteryx  (Fig.  894).  But  this 
is  not  a  true  socket-toothed  bird.  The 
so-called  teeth,  however,  are  only  denta- 
tions of  the  bony  edge  of  the  bill.  In  the  Eocene  of  the  Paris  basin 
was  found  a  gigantic  bird  (Gastornis)  ten  feet  in  height,  combining 
the  characters  of  a  wader  with  those  of  an  ostrich  (Fig.  893). 


Fie.  893.— Restoration  of  Gastornis 
Edwardsii  (after  Meunier). 


FIG.  804.— Skull  of  Odontopteryx  toliapicus,  restored  (after  Owen). 

In  1876  Cope  published  the  discovery  of  a  gigantic  bird  from  the 
lowest  Eocene  of  the  San  Juan  basin.  The  Diatryma  giyantea,  ac- 
cording to  Cope,  combines  the  characters  of  the  Cursores  (ostrich 
family)  with  those  of  the  extinct  Gastornis  of  the  Paris  basin.  Judg- 


522 


CENOZOIC  ERA— AGE  OF  MAMMALS. 


ing  from  its  foot,  it  was  double  the  size  of  an  ostrich.    This  is  the  first 
example  of  extinct  Cursores  found  in  North  America  (Cope). 

Mammals — General  Remarks. — 1.  We  have  already  seen  that  the  evo- 
lution of  this  class  may  be  traced  back  to  the  borders  of  the  Palaeozoic. 
The  probable  steps  are  :  1.  The  Hypotlieria,  represented  by  the  Thero- 
morphs  of  the  Permian ;  then  the  Protothena,  represented  by  hypo- 
thetical generalized  monotremes  of  the  Triass  ;  then  the  Metatheria  of 
Jurassic  and  Cretaceous ;  and,  finally,  the  Eutheria,  or  typical  placentals 
of  the  Tertiary.  2.  But  nothing  is  more  noteworthy  than  the  sudden- 
ness of  the  appearance  of  this  last  term  of  the  series.  We  find  only 
Mesozoic  types  even  to  the  borders  of  the  Tertiary  (Laramie),  and  then 
without  warning  there  appears  the  higher  type,  Eutheria,  of  the  Ter- 
tiary. This  might  be  explained  in  Europe,  where  there  is  unconform- 
ity at  this  horizon,  by  the  gap  in  the  record ;  but  here  in  America  the 
record  seems  almost  complete,  and  yet  at  the  same  horizon  a  great 
change  occurs.  It  is  impossible  to  explain  this  unless  we  admit  times 
of  rapid  evolution.  But  even  this  is  not  sufficient.  We  must  suppose, 
also,  that  these  new  types  appeared  here  in  America  by  migration 
about  the  end  of  the  Cretaceous  from  some  other  country,  where  we 
hope  yet  to  find  the  intermediate  links.  3.  Their  appearance  was  not 
only  sudden  but  in  great  numbers  and  considerable  variety.  In  the 
very  lowest  beds  of  the  Lower  Tertiary  (Puerco  beds)  Cope  finds  ninety- 
three  species,  and  already  all  the  main  divisions,  such  as  Carnivores, 
Herbivores,  Insectivores,  and  Primates.  4.  But,  although  these  main 
divisions  are  distinguishable,  they  are  not  yet  widely  separated,  as  we 
now  know  them.  At  that  time  there  were  no  typical  Carnivores, 
Herbivores,  etc.;  on  the  contrary,  they  were 'all  ^^generalized  types 
— i.  e.,  they  approached  each  other  very  closely,  as  shown  in  the  diagram 
(Fig.  895).  As  time  went  on,  not  only  were  they  separated  more  and 

more  by  adaptive  modification,  but 
also  divided  into  subordinate  branches 
(not  shown  in  the  diagram).  In  order 
to  indicate  the  fact  that  these  orders 
were  not  yet  distinctly  specialized,  it 
has  been  proposed  to  call  them  pro- 
Carnivores,  ^?r0-IIerbivores,  ^?'0-Si- 
miae,  etc. — j..  e.,  progenitors  of  these 
now  widely  distinct  orders.  They 
were  all  probably  five-toed  Planti- 
grades, with  tuberculated  molars 


TE 


CRETA  \ , 


EUTHR1UM 

FIG.  895.— Diagram  showing  Differentiation   (Bunodont),  and  therefore  Omnivores. 

of  Main  Orders  of  Tertiary  Mammals.          1.  .  ,-,  T  T  * 

By    tracing    the    divergent   lines   of 

the  diagram  downward,  they  meet  in  the   Cretaceous  in  a  hypothet- 
ical  ancestor,  which  was  probably  an  Insectivore.     5.  In  the  course 


TERTIARY   ANIMALS.  523 

of    the    Tertiary   the   mammalian    fauna    change    completely    many 
times. 

The  Tertiary  mammals  are  of  so  great  interest,  from  the  evolution 
point  of  view,  that  we  must  dwell  upon  them  somewhat  in  detail.    But 


Fio.  89G.-Tapirus  Indicus. 

it  Seems  impossible  to  present  selections  from  the  immense  mass  of 
material  at  hand  in  an  interesting  manner,  except  by  taking  a  few  clas- 
sic localities  from  different  epochs  and  different  countries,  and  briefly 
describing  what  has  been  found  in  each.  We  will  commence  with 
some  foreign  localities,  because  these  were  first  discovered  : 

1.  Eocene  Basin  of  Paris. — This  basin  has  been  made  celebrated  by 
the  labors  of  the  immortal  Cuvier.  The  discovery  in  the  early  portion 
of  the  present  century  of  »the  rich  treasures  imbedded  in  the  strata  of 


897.—  Palaeotherium  magnum,  x  ^  (after  Gaudry). 


this  basin,  and  the  consummate  skill  with  which  they  were  worked  up 
by  Cuvier,  gave  an  incredible  impulse  to  geology.  Fifty  species  of 
mammals,  of  which  forty  species  were  tapir-like  ;  ten  species  of  birds, 


524:  CENOZOIC  ERA— AGE  OF  MAMMALS. 

among  which  one,  the  Gastornis  (Fig.  893),  was  a  huge  wader  as  large 
as  an  ostrich ;  besides  reptiles,  fishes,  and  shells  in  abundance,  were 
discovered.  In  Eocene  times  the  Paris  basin  seems  to  have  been  an 
estuary  full  of  shells  and  fishes,  etc.,  into  which  the  bodies  of  birds  and 
mammals  were  drifted.  Among  the  many  remarkable  mammals  we  will 
select  two  as  types,  viz.,  the  Palceotliere  and  the  Anoplothere. 

The  PalaBothere,  like  the  Rhinoceros  and  like  some  of  the  earlier 
representatives  of  the  horse  family,  had  three  hoofed  toes  on  all  the 
feet.  It  is  usually  supposed  to  have  had  also  the  general  form  and  the 
short  flexible  snout  of  a  tapir  (Fig.  896),*  and  it  is  with  this  family  that 
Cuvier  supposed  it  has  its  nearest  alliance,  and  his  restoration  was  based 
on  this  view.  But  the  discovery  of  more  complete  skeletons  shows  that 


FIG.  898.— Anoplotherium  commune,  restored. 

the  neck  and  limbs  were  much, longer  than  had  been  supposed.  In 
general  form  (Fig.  897)  it  seems  to  have  been  as  much  like  the  horse 
family  as  the  tapirs. 

The  Anoplothere  was  a  slender  and  graceful  animal  without  snout, 
and  possessing  only  two  toes,  like  ruminants.  Most  of  its  characters, 
however,  allied  it  to  the  tapirs.  Among  these  characters  was  the  pos- 
session of  a  third  rudimental  or  non-functional  toe  (Cope)  and  a  full 
set  of  front  teeth.  It  was,  therefore,  a  remarkable  connecting  link 
between  the  tapirs  and  ruminants. 

2.  Siwalik  Hills,  India— Miocene.— Near  the  base  of  the  Himalayas 
occurs  a  range  of  hills  which  are  composed  of  fresh-water  uppermost 
Miocene  strata.  They  are  extremely  rich  in  vertebrate  and  especially 
in  mammalian  remains,  which  have  been  thoroughly  studied  by  Fal- 
coner. Eighty-four  species  of  mammals  are  described  from  this  locality. 
They  are  of  great  variety  of  forms,  both  Carnivora  and  Herbivora,  but 
the  latter  are  most  abundant.  Among  these,  perhaps  the  two  most 
remarkable  are  Dinotherium  \  and  Sivatherium. 

*  The  tapir  has  three  toes  on  the  hind-foot,  and  four  on  the  fore-foot,  but  the  outer 
one  is  small  and  not  functional. 

f  The  Dinothere  is  found  in  the  Miocene  of  India,  though  not  at  Siwalik. 


TERTIARY  ANIMALS. 


525 


The  Dinotliere  has  been  found  also  in  the  European  Miocene.     It 
was  a  huge  animal,  probably  the  largest  of  all  land  mammals  (Gaudry), 
with  a  skull  three  feet  long,  to  which  was 
attached  a  proboscis.     The  lower  jaw  was 
bent  downward,  and  carried  two  long,  tusk- 
like  teeth,  projecting  also  downward.     The 
whole  height  of  the  head,  from  the  points 
of  these  lower  teeth  to  the  top  of  the  cra- 
nium, was  five  feet. 

Recently  a  perfect  pelvis  has  been  found, 
showing  the  great  massiveness  of  these 
bones,  and  showing  also,  in  these  huge  ani- 
mals, the  existence  of  marsupial  bones* 
This  strange  animal  combined,  in  the  struct- 
ure of  its  head,  the  characters  of  Elephant,  via.  sco.— Head  of  Dinotherium 

'          .  '        giganteum,  greatly  reduced. 

Hippopotamus,  Tapir,  and  Dugong ;  but  it 

also  had  affinities  with  marsupials.     It  was  the  earliest  and  probably 
the  largest  of  Proboscidians. 

The  Sivathere  was  a  four-horned  antelope,  of  elephantine  size  and 
some  elephantine  characters.     The  four-horned  antelope  of  the  present 


Fio.  900.— Head  of  a  Sivatherium  gigantenm,  greatly  reduced. 

day  lives  in  the  same  locality,  but  is  a  comparatively  small  animal,  with 
two  short  conical  horns  from  the  front  part  of  the  frontal  bone,  and  two 

*  American  Journal  of  Science,  Series  II,  vol.  xxxviii,  p.  427. 


526 


CENOZOIC   ERA— AGE   OF   MAMMALS. 


somewhat  longer  ones  in  the  usual  place  on  the  back  part  of  the  same 
bone.  The  Sivathere,  on  the  other  hand,  was  of  elephantine  height, 
though  of  slenderer  form,  with  two  short  conical  horns  in  front,  and  two 
large,  palmately  branching  ones  behind.  The  form  of  the  nose-bones 
suggests  the  existence  of  a  snout.  The  feet  and  legs  were  clearly  those 
of  a  ruminant.  It  seems  to  have  combined  the  characters  of  a  Kumi- 
nant  and  a  Pachyderm.  The  Bramatliere  was  a  similar  animal,  of 
equally  gigantic  size,  found  in  strata  of  the  same  age. 

In  the  same  locality  were  found  also  three  species  of  Mastodons, 


FIG.  901.— Elephas  Ganesa,  x  &  (after  Falconer). 


seven  species  of  Elephants,  one  of  them  E.  ganesa-,  remarkable  for  the 
prodigious  length  and  size  of  its  tusks ;  three  species  of  the  Horse  fam- 


Fio.  902.— Skeleton  of  Hipparion  gracile,  restored  (after  Gaudry). 

ily ;  five  species  of  Khinoceros ;  four  to  seven  species  of  Hippopotamus, 
and  three  species  of  hog;  also,  Anoplotheres,  Camels,  Camelopards, 


TERTIARY   ANIMALS. 


527 


Oxen,  Sheep,  Antelope,  Musk-ox,  Monkeys,  etc. ;  also,  many  Reptiles, 
among  which  were  narrow-nosed  Crocodiles,  like  the  Gavials  now  liv- 


Fio.  903.—  Mesopithecus  Pentelici,  restored  x  J  (after  Gaudry). 

ing  in  the  Ganges,  and  the  huge  Turtle,  Colossochelys,  already  men- 
tioned (p.  520). 

The  most  characteristic  representative  of  the  Horse  family  in  the 


FIG.  904. — A,  Skull  of  Machairodns  cnltridens,  without  the  lower  jaw,  reduced  in  size;  B,  Canine 
Tooth  of  the  same,  one  half  the  natural  size.    Pliocene,  France. 

Old  World  Miocene  was  a  three-toed  animal  called  Hipparion.     A 
restoration  of  this  graceful  creature  is  given  in  Fig.  902. 


528 


CEXOZOIC  ERA— AGE  OF  MAMMALS. 


In  the  Miocene  and  Pliocene  of  Europe  are  first  found  remains  of  that 
most  destructive  of  carnivores,  the  saber-toothed  tiger — Machairodus 
(Fig.  904).  In  the  Miocene  of  Europe,  also,  the  first  true  Monkeys 
(Fig.  903)  were  introduced  (Flower).  Before  this,  there  were  only 
lemurs  or  Prosimiae. 

Perhaps  it  is  well  to  call  attention  to  the  fact  that,  while  the 
tapir-like  Pachyderms  predominate  in  the  Eocene,  the  huge  forms, 
e.  g.,  Rhinoceros  and  Hippopotamus  family,  and  Proboscidians, 
were  first  introduced  and  immediately  became  abundant  in  the  Mio- 
cene. 

American  Localities. — 3.  Marine  Eocene  of  Alabama. — We  select 
this  as  an  example  of  American  marine  Eocene.  At  Claiborne,  Ala- 
bama, according  to  Lyell,  there  occur  no  less  than  400  species  of  shells, 
besides  many  Echinoderms,  and  abundance  of  sharks'  teeth.  But  the 
most  remarkable  remains  found  there  are  those  of  an  extinct  whale — 
Zeuglodon  cetoides — so  called  from  the  yoke-like  form  of  the  double- 
fanged  molar  teeth,  which  were  six  inches  in  length 
(Fig.  905).  The  skull  was  long  and  pointed  (Fig. 
906),  and  set  with  the  double-fanged  teeth  behind 
and  conical  ones  in  front.  The  vertebrae,  which  are 
in  such  abundance  that  they  are  used  for  making 
fences  and  even  burned  by  farmers  to  rid  the  fields 
of  them,  are,  some  of  them,  eighteen  inches  long  and 
twelve  inches  in  diameter  (Dana),  and  the  vertebral 
column  has  been  found  in  place  nearly  seventy  feet 
long  (Lyell).  The  animal  must  have  been  more 
than  seventy  feet  long,  and  the  remains  of  at  least 
forty  individuals  have  been  found  (Lyell).  They  have 
been  found  in  southern  Georgia  as  well  as  in  Ala- 
bama, and  probably  their  range  was  quite  extensive. 
This  animal  is  peculiarly  interesting  as  the  first  appearance  of  the 
very  distinct  order  Cetacea.  No  intermediate  links  have  yet  been 
found  connecting  this  with  other  orders  of  mammals,  or  with  the  great 


Fm.  905.— Tooth  of 
Zeuglodon  cetoides, 
x  |  (after  Gaudry). 


FIG.  908.— Head  of  Zeuglodon  cetoides,  x  ^  (after  Gaudry). 

reptiles.     And  yet,  from  their  large  size  and  marine  habits,  they  are 
more  likely  than  land  mammals  to  have  been  found,  if  they  existed  in 


TERTIARY  ANIMALS. 


529 


earlier  or  Cretaceous  times.  The  origin  of  whales  is  not  known,  al- 
though they  probably  came  from  land  mammals  by  retrograde  changes 
adapted  for  aquatic  life. 

The  Atlantic  and  Gulf  border  strata  are  of  course  all  marine,  and 
therefore  contain  very  few  land-animals.  It  is  to  the  fresli-water  'ba- 
sins of  the  interior  that  we  must  look  for  a  full  record  of  the  mam- 


Pio.  907.— Vertebra  and  Tooth  of  Zeuglodon  cetoides,  reduced. 

malian  fauna  of  America  in  Tertiary  times.  These  basins  furnish  the 
fullest  and  most  continuous  record  of  the  whole  Tertiary  which  has 
ever  yet  been  found.  The  Early  Tertiary  fauna  of  America  was  wholly 
different  in  species  and  in  genera,  and  even  largely  in  families,  from 
that  of  Europe.  This  shows  that  the  two  continents  were  then  as  now 
widely  separated.  It  will  be  best  to  take  them  in  the  order  of  their 
age,  as  we  can  thus  best  show  the  evidences,  if  any,  of  derivation  of  the 
later  from  the  earlier  faunae. 

4.  San  Juan  Basin— Puerco  Beds — Lowest  Eocene. — In  these,  the 
very  lowest  part  of  the  Lower  Eocene — so  low  that  they  are  regarded  by 
some  even  as  partly  Laramie — Cope  has  found  a  great  number  of  most 
extraordinary  mammals,  more  generalized  than  any  before  known. 
These  earliest  true  mammals  seem  to  have  been  very  abundant,  for,  out 
of  106  species  of  vertebrates  found,  93  were  mammals.  They  represent 
already  all  the  main  divisions  of  the  Mammalian  class.  Besides  marsu- 
pials continued  from  the  Mesozoic,  there  were  Carnivores,  Herbivores, 
Insectivores,  and  Lemurine  Primates ;  but  in  forms  so  generalized  that 
they  scarcely  deserve  these  names,  and  may  well  be  called  Pro-Car- 
nivores, Pro-Herbivores,  etc.,  or  progenitors  of  these  now  widely-dis- 
tinct orders.  The  remains  of  these  animals  are  not  so  perfect  as  those 
on  higher  horizons.  We  select  for  illustration  an  almost  perfect  hind- 
limb  of  the  Periptychus  of  Cope,  one  of  the  most  generalized  of  known 
animals.  It  is  seen  that  the  foot-structure  is  perfectly  generalized  and 
the  tread  completely  plantigrade.  It  is  an  admirable  example  of  the 
primitive  foot. 
34 


530 


CENOZOIC  ERA— AGE  OF  MAMMALS. 


FIG.  908.—  Periptychus  Rhabdodon  :  A,  Hind-foot,  x  £  ;  B,  Hind-  limb,  x  J  (after  Osborn) 


5.  Green  River  Basin  —  Wahsatch  Beds  —  Lower  Eocene.  —  Imme- 
diately above  the  last,  but  still  in  the  Lower  Eocene,  is  found  another 
mammalian  fauna  equally  abundant  in  species  and  equally  remarkable, 


FIG.  909.— An  almost  perfect  Skeleton  of  a  Phenacodus  primsevus  (after  Cope). 

but  almost  wholly  different.  From  this  fauna  we  select  two,  Phenacodus 
and  the  Coryplwdon  (peak-tooth).  The  Phenacodus  (Fig.  909)  is 
probably  the  most  generalized  mammal  known.  It  may  be  regarded 


TERTIARY  ANIMALS. 


531 


as  the  ancestor  of  the  Ungulates,  or  hoofed  animals,  but  with  almost 
equal  right  may  be  claimed  as  the  ancestor  of  other  orders.  It  was 
five-toed,  each  toe  provided  with  a  flat  nail,  which  was  neither  claw 
nor  hoof,  but  between  the  two.  It  had  bunodont  molars,  a  full  com- 
plement of  unmodified  teeth,  and  foot-bones.  It  was,  therefore,  prob- 
ably omnivorous  in  habit.  Cope  has  described  nine  species  partly  from 
this  horizon  and  partly  from  the  previous.  They  were  about  the  size 
of  a  sheep,  or  perhaps  a  little  larger.  The  CorypJwdon  was  a  genus  of 
large  animals,  of  very  generalized  structure,  uniting  the  characters  of 
the  more  generalized  Ungulates,  such  as  Tapirs,  with  those  of  the  more 
generalized  Carnivores,  such  as  Bears.  They  were  five-toed  Ungulates 
with  full  number  of  unmodified  foot-bones,  and  a  tread  somewhat  like 
that  of  an  Elephant.  Eight  or  ten  species  of  Coryphodontidse  have 
been  described,  varying  in  size  from  that  of  a  Tapir  to  that  of  an  ox  or 
larger  (Fig.  910). 


17 


FIG.  910. — Coryphodon  Hamatus  (after  Marsh):  A.  Head,  showing  form  of  the  brain,  x  $;  B,  Hiiid- 

foot;  C,  Fore-foot,  x  $. 

In  the  same  beds  are  found  the  remains  of  what  is  believed  to  be 
the  earliest  progenitors  of  the  horse  family,  viz.,  the  Eohippus  (dawn- 
horse).  This  was  a  small  animal  about  the  size  of  the  fox,  with  three 


532 


CENOZOIC  ERA— AGE   OF   MAMMALS. 


hoofed  toes  on  the  hind-feet,  and  four  functional  toes,  a  fifth  meta- 
carpal,  and  a  corresponding  rudimentary  fifth  toe  on  the  fore-feet. 

As  already  said,  generalized  Carnivores,  Insectivores,  and  lemurine 
monkeys,  Pro-Simice,  are  found  on  this  and  the  previous  horizon. 

6.  Green  River  Basin— Bridger  Beds — Middle  Eocene. — From  this 
wonderful  fresh-water  deposit  there  have  been  described  by  Marsh, 
Cope,  and  Leidy,  150  species  of  vertebrates,  of  which  the  larger  number 
are  mammals.  This  shows  a  marvelous  abundance  of  mammalian  life 
in  this  early  Tertiary  time.  The  most  numerous  of  these  are  tapir-like 
animals,  such  as  Hyracliyus,  Limnohyus  (Palceosyops — Fig.  913),  etc. ; 
but  the  most  formidable  are  the  Dinocerata,  an  order  established  by 
Marsh  and  including  the  genera  Dinoceras  (Marsh),  Uintatlierium 
(Leidy),  and  Tinoceras  (Marsh),  or  Loxolopliodon  (Cope).  The  re- 


%  £3 


FIG.  911.—  Dinoceras  mirabile,  x  |  (after  Marsh):  A,  Skull;  B,  Hind-foot,  x  J;  C,  Fore-foot,  x 


mains  of  thirty  species  and  more  than  one  hundred  and  fifty  distinct 
individuals  of  this  order  have  been  obtained  from  the  Middle  Eocene 


TERTIARY   ANIMALS. 


533 


of  Wyoming  and  deposited  in  the  Museum  of  Yale  College,  where  they 
have  been  carefully  studied. 

The  type  genus  of  this  order  is  the  Dinoceras.  Almost  every  bone 
in  the  skeleton  of  this  animal  is  now  known.  Although  elephantine 
in  size,  there  is  no  evidence  in  the  skull  of  the  existence  of  a  proboscis ; 
the  proportions  of  the  neck  and  fore-limbs^  furthermore,  show  that 
its  presence  was  unnecessary.  Three  pairs  of  horns  are  indicated  by 
the  projecting  cores  (Fig.  911),  one  pair  of  which  stood  far  in  front 
on  the  nasal  bones,  another  on  the  maxillary  bones  immediately  above 
the  canines,  and  a  third  and  much  larger  pair  farther  back  on  the 
parietal  bones.  This  last  pair  were  sheathed  with  a  thickened  integu- 
ment, which  may  have  developed  into  true  horn,  as  in  the  Prong-horned 
Antelope.  The  three  pairs  of  elevations  are  present  in  both  sexes,  but 
proportionally  smaller  in  the  females.  In  addition  to  these  formidable 
weapons,  both  sexes  were  provided  with  canine  tusks,  those  of  the  males 
being  very  powerful,  in  some  cases  seven  or  eight  inches  in  length. 

The  largest,  most  specialized,  and  latest  of  the  Dinocerata  was  the 
huge  monster  Tinoceras.  The  head  of  this  animal  was  four  feet  in 
length,  and  the  horn-cores  much  longer  than  in  Dinoceras.  Fig.  912 
is  a  restoration  by  Marsh  of  this  magnificent  animal. 


FIG.  912.— Restoration  of  Tinoceras  ingens,  x  ^j  (after  Marsh). 

The  animals  of  this  entire  order  seem  to  have  been  quite  abundant 
for  a  short  time  during  the  latter  part  of  the  Middle  Eocene.  They 
then  became  extinct,  leaving  apparently  no  successors,  though  possibly 
the  Elephant  tribe  of  to-day  may  be  their  greatly  modified  descend- 


534: 


CENOZOIC  ERA— AGE  OF  MAMMALS. 


ants.  Their  feet  were  provided  each  with  five  toes  (Fig.  911),  and  the 
brain  was  proportionally  smaller  than  in  any  other  land  mammal. 

Another  extraordinary  group  of  animals  discovered  by  Marsh  in  the 
Eocene  beds  has  been  placed  by  him  in  a  new  order  called  Tillodontia 
(Fig.  914).  These  animals  combine  the  head  and  claws  of  a  bear  with 
the  incisors  of  a  Eodent  and  the  general  characters  of  Ungulates.  The 
order  must  be  regarded,  therefore,  as  a  remarkable  generalized  type. 

We  have  seen  the  earliest  in  the  line  of  descent  of  the  horse  family 
— Eoliippus — in  the  Lower  Eocene  Wahsatch  beds.  In  the  Middle 


FIG.  913.—  Limnohyus  (Palaeosyops)  (after  Leidy). 

Eocene  Bridger  beds  we  find  the  next  in  the  series — the  Oroliippus 
(mountain-horse).     This  was  of  similar  size;   but  already  the  fifth 


FIG.  914.— EOCENE  MAMMAL:  Skull  of  Tillodontia  (after  Marsh). 

metacarp  and  rudimentary  toe  are  gone,  and  there  were  now  three 
hoofed  toes  on  the  hind-feet  and  four  functional  toes  on  the  fore-feet. 


TERTIARY  ANIMALS.  535 

Although  the  Herbivores  predominated,  there  were  many  mammals 
belonging  to  other  orders.  For  example,  there  were  species  allied  to 
the  Cat,  Wolf,  and  Fox  ;  also,  Bats,  Squirrels,  Moles,  and  Marsupials  ; 
also  many  Monkeys  allied  to  the  Lemurs,  Marmosets,  etc.,  but  more 
generalized  than  any  living  Lemur. 

7.  Mauvaises  Terres  of  Nebraska—  White  River  Basin—  Miocene.— 
From  this,  the  earliest  discovered  of  the  Tertiary  basins  of  the  West 
(see  Fig.  843,  p.  504),  have  been  collected  by  Hayden  and  described  by 
Leidy  more  than  40  species  of  mammals,  of  which  25  are  Ungulates, 
8  Carnivores,  and  the  remainder  mostly  Rodents.  Many  other  species 
have  been  discovered  in  the  same  locality  since  that  time.  All  the 
species,  nearly  all  the  genera,  and  many  even  of  the  families,  are  entirely 
different  from  those  found  in  the  preceding  epoch,  and  much  more 
modern.  Although  the  tapir-like  animals  still  prevail,  species  of  the 
deer,  the  camel,  the  horse,  and  the  dog  families  are  added.  This  is 
seen  in  the  following  schedule  : 

Hyena.     "j 
Jg£       L  Allies. 

Panther.  J 
Rhinoceros  family. 
Brontotheridae. 


Camel    " 
[  Horse    " 
Rodents. 
Turtles. 

The  most  extraordinary  animals  of  this  time  were  the  Brontotheri- 
dae. This  family,  according  to  Marsh,  included  the  Brontotherium, 
the  Menodus  (Titanotherium),  the  Brontops,  and  several  other  genera. 
They  were  of  elephantine  size,  with  singular,  saddle-shaped  head  like  a 
Rhinoceros,  and  with  at  least  one  pair  of  large  horns  on  the  maxillaries. 
These  are  sometimes  enormously  elongated.  Fig.  915  is  a  restoration 
of  Brontops  by  Marsh. 

They  had  some  affinities  with  their  predecessors  the  Dinoceras,  but 
their  nearest  allies  are  the  Rhinoceros  and  the  Tapirs.  Like  the  latter, 
they  had  three  hoofed  toes  on  the  hind-feet  and  four  on  the  fore-feet. 

Several  of  the  horse  family  are  found  in  the  Miocene,  especially  the 
Nesoliippus  and  the  Miohippus.  These  had  lost  the  fourth  toe  on  the 
fore-feet  possessed  by  the  Oroliippus,  and  therefore  had  three  toes  on 
all  the  feet,  They  may  be  regarded  as  the  first  of  the  true  horse  family, 
Equidce.  These  three-toed  horses  were  about  the  size  of  a  sheep. 

The  Oreodon  was  another  remarkable  animal  of  generalized  struct- 
ure, intermediate  between  the  Hog,  the  Deer,  and  the  Camel,  which 
at  this  time  inhabited  in  great  numbers  the  whole  continent  from 


536 


CENOZOIC  ERA— AGE   OF  MAMMALS. 


FIG.  915.—  Brontops,  restored  by  Marsh,  x 


Nebraska  to  Oregon.  Thirty-five  species  of  Oredontidas  are  known, 
although  not  all  from  this  horizon.  The  head  of  one  is  given  below 
(Fig.  916). 


FIG.  916.— Oreodon  Culbertsoni  (after  Gaudry). 

The  Miocene  of  Oregon — John  Day  basin — is  equally  rich  in  re- 
mains of  all  the  families  mentioned  above.  Among  Carnivores,  besides 
many  species  of  the  Cat  family,  Cope  has  described  ten  species  of  the 
Dog  family. 

It  is  well  to  note  that  in  the  Miocene,  for  the  first  time,  existing 
families  of  mammals  began  to  appear.  We  have  here  the  families  of 
the  dog,  the  cat,  the  deer,  the  camel,  the  horse,  and  the  rhinoceros.  It 


TERTIARY  ANIMALS. 


537 


is  well  to  note  also  that  the  American  Continent,  as  shown  by  the 
uniqueness  of  its  mammalian  fauna  was  still  completely  isolated. 

8.  Mauvaises  Terres — Niobrara  Basin— Loup  Fork  Beds— Pliocene. 
— In  nearly  the  same  locality  overlying  the  last,  but  extending  farther 
south,  occur  lake-deposits  of  the  Pliocene  times,  full  of  mammalian  re- 
mains, but  again  wholly  different  in  species.  Among  Ungulates  there 
was  a  Rhinoceros,  as  big  as  the  Indian  species ;  an  Elephant  (E.  Ameri- 
canus),  the  same  which  lived  in  the  Qua- 
ternary, bigger  than  any  now  living ;  a  Mas- 
todon, but  smaller  than  the  great  Mastodon 
of  the  Quaternary ;  a  large  number  of  the 
horse  family  and  several  of  the  camel  fami- 
ly, besides  many  other  families  of  Ungu- 
lates, Carnivores,  Rodents,  etc.  Both  the 
horse  and  the  camel  family  were  more  nu- 
merously represented  at  that  time  in  America 
than  in  the  Eastern  Continent.  In  fact,  it 
is  not  at  all  improbable  that  they  originated 
here,  and  emigrated  to  the  other  continent. 

From  the  presence  of  Elephants,  Mastodons,  Rhinoceros,  Camels,  and 
Horses  on  both  continents,  we  conclude  that  the  two  continents  were 
probably  connected  in  Pliocene  times. 

Among  the  horse  family  found  here,  the  most  interesting,  as  show- 
ing the  gradual  approach  toward  the  modern  horse,  are  the  Protohippus 
and  the  Pliohippus.  These  were  larger  than  the  Miocene  horses,  being 
about  the  size  of  the  ass.  The  former  was  three-toed,  but  the  two  side- 
toes  were  smaller  and  shorter  and  scarcely  functional,  unless  on  marshy 
ground ;  the  latter  had  already  lost  the  side-toes,  and  was  almost  but 
not  quite  a  perfect  horse. 

We  see  here  for  the  first  time  existing  genera.  Elephas,  Canis,  and 
in  the  higher  beds  Equus  begin  to  appear,  but  not  yet  existing  species. 


TERTIARY 


Rhinoceros. 

Elephant. 

Mastodon. 

Three  of  the  Camel  family. 

Five  of  the  Horse        " 

Oreodon. 

Deer. 

Fox. 

Wolf. 

Tiger. 

Beaver. 

Porcupine. 


Pio.  917.— The  Successive  Appearance  and  Increasing  Percentage  of  Existing  Orders,  Families, 
Genera,  and  Species  of  Mammals. 

for  these  do  not  appear  until  the  Quaternary.  The  successive  appear- 
ance and  increasing  percentage  of  existing  orders,  families,  genera,  and 
species  of  mammals,  is  shown  in  a  very  general  way  in  the  accompany- 
ing diagram. 


538 


CENOZOIC  ERA— AGE   OF  MAMMALS. 


Some  General  Observations  on  the  Tertiary  Mammalian  Fauna.— 1. 
Size  of  Brain. — Lartet  has  shown  that  the  brain-cavity  of  some  of  the 


FIG.  920. 

FIGS.  918-920.— BRAINS  op  CORYPHODON,  DINOCERAS.  AND  BRONTOTHERITTM,  COMPARED  (after 
Marsh):  918.  Coryphodon,  Skull  and  Brain,  x  £.  919.  Dinoceras,  Skull  and  Brain,  x  J.  920. 
Brontotherium,  Skull  and  Brain,  x  ^. 


TERTIARY   ANIMALS.  539 

Tertiary  animals  is  decidedly  smaller  relatively  than  that  of  their  liv- 
ing congeners.  Marsh  has,  moreover,  traced  a  gradual  increase  in  the 
relative  size  of  the  brain  from  the  earliest  Eocene  to  the  present  time. 
The  brain  of  the  Coryphodon,  Lower  Eocene,  is  not  only  extremely 
small  in  proportion  to  the  size  of  the  animal,  but  the  higher  portion  of 
the  brain — the  cerebral  lobes — is  very  small  in  proportion  to  the  cere- 
bellum. The  brain  of  the  Middle  Eocene  Dinoceras  is  only  about  one 
eighth  the  size  of  that  of  a  living  Rhinoceros  of  equal  bulk.  The  brain 
of  the  Miocene  Brontothere  is  larger  than  that  of  the  Eocene  Dino- 
ceras, but  much  smaller  than  that  of  the  Pliocene  Mastodon  of  nearly 
the  same  size.  Through  the  whole  line  of  ancestry  of  the  horse  the 
gradually-increasing  size  of  the  brain  may  be  traced  step  by  step.  As 
already  seen,  page  491,  the  same  was  true  of  early  birds  and  reptiles. 
There  has  been  a  gradual  increase  in  brain-power,  and  therefore  in 
nerve  and  muscular  energy,  in  all  classes. 

2.  Genesis  of  Existing  Orders. — We  have  seen  that  the  main  branches 
of  the  Mammalian  class  if  traced  backward,  approach  one  another  very 
closely  in  the  Early  Tertiary ;  and  if  we  could  trace  them  still  further 
back,  they  would  unite  in  the  Cretaceous  in  a  common  stem  or  primal 
mammal.    This  was  doubtless  a  plantigrade,  five-toed,  bunodont,  omniv- 
orous animal.    From  this  common  stem  the  Carnivores  and  the  Ungu- 
lates— to  take  only  the  two  most  widely-contrasted  types — diverged  more 
and  more  in  all  these  characters — the  one  becoming  more  and  more 
adapted  to  flesh-eating,  the  other  to  herb-eating ;  the  one  for  seizing, 
the  other  for  escaping — until  the  present  extreme  types  were  attained. 

3.  Genesis  of  Existing  Families. — Not  only  did  these  two  main 
branches  separate  more  and  more,  but  each  of  them  branched  again  to 
form  existing  families.     To  illustrate  this  we  take  the  order  of  Ungu- 
lates as  the  best  known. 

Cuvier  divided  all  Ungulates  into  two  orders,  viz.,  Pachyderms  and 
Ruminants.  The  Pachyderms  are  a  heterogeneous  order,  but  the  Ru- 
minants have  been  regarded  as  one  of  the  most  distinct  of  all  mamma- 
lian orders.  Their  horns  in  pairs,  their  hoofs  in  pairs,  absence  of  upper 
front-teeth,  complex  stomachs,  and  the  habit  of  rumination,  differenti- 
ated them  widely  from  all  other  animals.  But  Prof.  Owen  showed  that 
this  distinction,  so  clear  in  zoology,  was  untenable  in  paleontology. 
He  found,  in  studying  extinct  Ungulates,  that  another  distinction,  viz., 
foot-structure,  was  more  fundamental  and  persistent.  He  therefore 
divided  all  Ungulates  into  Perissodactyls  (odd-toed)  and  Artiodactyls 
(even-toed).  A  Perissodactyl  may  have  five  toes,  as  in  the  Corypho- 
don  and  the  Elephant ;  or  three  toes,  as  in  the  Palaeothere,  the  Rhi- 
noceros, and  the  Tapir ;  or  one  toe,  as  in  the  Horse.  The  Artiodactyls 
always  have  their  toes  in  pairs :  there  may  be  only  two  toes,  as  in 
Anoplothere  and  in  Ruminants ;  or  four,  as  in  the  Hog  and  the  Hippo- 


540 


CENOZOIC  EKA— AGE  OF  MAMMALS. 


potamus.  Owen,  indeed,  made  the  Elephant,  Mastodon,  etc.,  a  distinct 
order,  under  the  name  of  Proboscidians,  but  these  are  probably  best 
regarded  as  a  very  distinct  offshoot  or  sub-order  of  the  Perissodactyls. 


PRIMAL  UNGULATE. 

{PHENACODUS.) 

FIG.  921.— Diagram  illustrating  the  Differentiation  of  the  Different  Families  of  Ungulates. 

Now  in  the  Earliest  Tertiary  the  sub-orders  Artiodactyls  and  Peris- 
sodactyls were  united  in  a  common  ancestor  or  primal  Ungulate,  from 
which  they  afterward  separated.  The  Phenacodus  of  Cope  (Fig.  909, 
p.  530)  seems  to  be  such  a  primal  Ungulate.  Each  of  the  primary 
branches  then  divided  and  again  divided,  until  the  extreme  branch  in 
one  direction  became  the  Horse,  and  the  extreme  branch  in  the  other 
direction  the  Ox.  In  the  tree  above  we  have  attempted,  in  a  general 
way,  to  represent  the  differentiation  of  the  several  orders  of  Ungulates, 
The  Cuvierian  orders,  Pachyderms  and  Ruminants,  are  indicated  by  a 
vinculum.  It  is  seen  at  a  glance  why,  in  studying  living  animals  alone, 
the  Ruminants  seem  so  distinct. 

Genesis  of  the  Horse. — In  conclusion,  it  will  be  interesting  and  in- 
structive to  run  out  one  of  these  branches  and  show  in -more  detail  the 
genesis  of  one  of  the  extreme  forms.  For  this  purpose  we  select  the 
Horse,  because  it  has  been  somewhat  accurately  traced  by  Huxley  and 
by  Marsh.  About  thirty-five  or  forty  species  of  this  family,  ranging 
from  the  earliest  Eocene  to  the  Quaternary,  are  known  in  the  United 
States.  The  steps  of  evolution  may  therefore  be  clearly  traced. 

In  the  lower  part  of  the  Eocene  basin  ( Coryphodon  beds)  of  Green 
Eiver  is  found  the  earliest  known  animal  in  the  direct  line  of  descent  of 
the  horse  family,  viz.,  the  recently-described  Eoliippus  of  Marsh.  This 
animal  had  three  toes  on  the  hind-foot  and  four  perfect,  serviceable  toes 
on  the  fore-foot ;  but,  in  addition,  on  the  fore-foot  an  imperfect  fifth 


TERTIARY   ANIMALS.  541 

metacarpal  (splint),  and  possibly  a  corresponding  rudimentary  fifth  toe 
(the  thumb),  like  a  dew-claw.  Also,  the  two  bones  of  the  leg  and  fore- 
arm were  yet  entirely  distinct.  This  animal  was  no  larger  than  a  fox. 
Next,  in  the  Middle  Eocene  (Bridger  beds),  came  the  Orohippus  of 
Marsh,  an  animal  of  similar  size,  and  having  similar  structure,  except 
that  the  rudimentary  thumb  or  dew-claw  is  dropped,  leaving  only  four 
toes  on  the  fore-foot.  Next  came,  in  the  Lower  Miocene,  the  Mesohip- 
pus,  in  which  the  fourth  toe  has  become  a  rudimentary  and  useless 
splint.  Next  came,  still  in  the  Miocene,  the  Miohippus  of  the  United 
States  and  nearly-allied  Anchithere  of  Europe,  more  horse-like  than  the 
preceding.  The  rudimentary  fourth  splint  is  now  almost  gone,  and  the 
middle  hoof  has  become  larger;  nevertheless,  the  two  side-hoofs  are 
still  serviceable.  The  two  bones  of  the  leg  have  also  become  united, 
though  still  quite  distinct.  This  animal  was  about  the  size  of  a  sheep. 
Next  came,  in  the  Upper  Miocene,  and  Lower  Pliocene,  the  Protohip- 
pus  of  the  United  States  and  allied  Hipparion  of  Europe,  an  animal 
still  more  horse-like  than  the  preceding,  both  in  structure  and  size. 
Every  remnant  of  the  fourth  splint  is  now  gone ;  the  middle  hoof  has 
become  still  larger,  and  the  two  side-hoofs  smaller  and  shorter,  and  no 
longer  serviceable,  except  in  marshy  ground.  It  was  about  the  size  of 
the  ass.  Next  came,  in  the  Pliocene,  the  Pliohippus,  almost  a  complete 
horse.  The  hoofs  are  reduced  to  one,  but  the  splints  of  the  two  side- 
toes  remain  to  attest  the  line  of  descent.  It  differs  from  the  true  horse 
in  the  skull,  shape  of  the  hoof,  the  less  length  of  the  molars,  and  some 
other  less  important  details.  Last  comes,  in  the  Quaternary,  the  mod- 
ern horse — Equus.  The  hoof  becomes  rounder,  the  splint-bones  shorter, 
the  molars  longer,  the  second  bone  of  the  leg  more  rudimentary,  and 
the  evolutionary  change  is  complete. 

Similar  gradual  changes,  becoming  more  and  more  horse-like,  may 
be  traced  in  the  shape  of  the  head  and  neck,  and  especially  in  the  grad- 
ually-increasing length  and  complexity  of  structure  of  the  grinding- 
teeth.  All  these  changes  are  shown  in  Fig.  922,  for  which  we  are  in- 
debted to  the  kindness  of  Prof.  Marsh.  The  Eohippus  is  omitted,  as 
no  figures  of  this  have  yet  been  published. 

There  can  be  no  doubt  that  if  we  could  trace  the  line  of  descent  still 
further  back  we  would  find  a  perfect  five-toed  ancestor.  From  this 
normal  number  of  five,  the  toes  have  been  successively  dropped,  ac- 
cording to  a  regular  law.  In  the  Perissodactyl  line  first  the  thumb, 
No.  1,  was  dropped ;  then  the  little  finger,  No.  5 ;  then  the  first  and 
ring-fingers,  Nos.  2  and  4,  were  shortened  up  more  and  more  and  finally 
disappeared,  and  only  the  middle  finger,  No.  3,  remained  in  the  modern 
horse.  In  the  Artiodactyl  line,  after  the  dropping  of  No.  1,  then  Nos. 
2  and  5  of  the  four-toed  foot  were  shortened  and  gradually  disappeared, 
and  Nos.  3  and  4  remained  in  the  ruminants. 


542  CEXOZOIC  ERA— AGE   OF   MAMMALS. 

In  a  similar  way  Cope  has  traced  the  line  of  descent  of  the  camel 


Equns:  Quaternary  and 
Eecent 


Pliohippus:  Pliocene. 


Protohippus:  Lower  Pliocene. 


Hiohippus:  Miocene. 


Mesohippus:  Lower  Miocene. 


Orohippus:  Eocene. 


Fro.  922.— Diagram  illustrating  Gradual  Changes  in  the  Horse  Family.  Throughout  a  is  fore-foot; 
b,  hind-foot:  c,  fore-arm:  d,  ehank;  e,  molar  on  side  view;  /and  </,  grinding  surface  of  upper 
and  lower  molars.  (After  Marsh.) 


GENERAL   OBSERVATIONS  ON  THE   TERTIARY  PERIOD.  543 

from  the  Pantolestes  of  the  Early  Eocene,  through  the  Poebrotherium 
of  the  Miocene,  and  the  Procamelus  of  the  Pliocene,  to  the  modern 
camel.*  Similarly  also  the  modern  deer,  with  its  branching  antlers, 
may  be  traced  from  the  Lower  Pliocene,  where  they  had  antlers  of  one 
or  two  points  through  the  Upper  Pliocene,  where  the  antlers  are  more 
complex,  to  the  magnificent,  many-branched  antlers  of  the  Quaternary 
and  modern  times. 

From  the  earliest  and  most  generalized  types,  therefore,  to  the  pres- 
ent specialized  types,  the  principal  changes  have  been,  first,  from  planti- 
grade to  digitigrade;  second,  from  short-footed  digitigrade  to  long- 
footed  digitigrade,  i.  e.,  increasing  elevation  of  the  heel;  third,  from 
five  toes  to  one  toe  in  the  Horse,  or  two  toes  in  Ruminants;  and, 
fourth,  from  simple  omnivorous  molars  to  the  complex  herbivorous 
millstones  of  the  Horse  and  the  Ox. 

The  change  from  plantigrade  to  digitigrade,  with  increasing  eleva- 
tion of  the  heel,  when  taken  in  connection  with  increasing  size  of  the 
brain,  and  therefore  presumably  with  increasing  brain-power,  shows  a 
gradual  improvement  of  structure  adapted  for  speed  and  activity,  and  a 
pari-passu  increase  of  nervous  and  muscular  energy,  necessary  to  work 
the  improved  structure. 

4.  Not  only  does  the  mammalian  fauna  of  the  Miocene  differ  com- 
pletely from  that  of  the  Eocene,  which  precedes,  and  from  the  Pliocene, 
which  succeeds  it,  but  there  seem  to  have  been  at  least  three  distinct 
Eocene  and  two  distinct  Miocene  faunas.  Thus  there  have  been  many 
complete  changes  in  the  mammalian  fauna  in  Tertiary  times. 

General  Observations  on  the  Tertiary  Period. 

"We  have  already  seen  (p.  470)  that  during  Cretaceous  times  a  wide 
sea  occupying  the  position  of  the  Western  Plains  and  Plateau  region, 
divided  America  into  two  Continents,  an  Eastern  and  a  Western.  We 
have  also  seen  (p.  495)  that  at  the  end  of  the  Cretaceous,  this  sea  was 
obliterated  by  continental  upheaval,  and  the  continent  became  one. 
During  the  Eocene,  the  eastern  portion  of  the  place  formerly  occupied 
by  this  sea  was  probably  dry  land,  but  in  the  Plateau  region  there 
were  great  fresh-water  lakes,  one  north  of  the  Uintah  Mountains, 
Green  River  Basin,  and  one  south  of  the  same,  and  probably  one  in 
Oregon.  There  were  possibly  others  yet  unknown.  At  the  end  of 
the  Eocene,  there  was  a  rise  in  the  Plateau  region,  which  drained  the 
Eocene  lakes,  through  the  Colorado  River,  and  a  corresponding  depres- 
sion in  the  Plains  region  on  the  one  side,  and  the  Basin  region  on  the 
other,  not  sufficient  to  form  a  sea  again,  but  sufficient  to  form  great 
Miocene  lakes  there.  During  the  Miocene,  the  bared  bottoms  of  the 

*  American  Naturalist,  vol.  xx,  p.  611,  1886. 


544:  CENOZOIC   ERA— AGE   OF  MAMMALS. 

Eocene  lakes  were  subject  to  prodigious  erosion,  and  much  of  the  gen- 
eral erosion  of  the  Plateau  region  occurred  at  that  time.  At  the  end  of 
the  Miocene  occurred  the  greatest  event  of  the  Tertiary  period,  one  of 
the  greatest  in  the  history  of  the  American  Continent.  At  that  time 
the  sea-bottom  off  the  then  Pacific  coast  was  crushed  together  into  the 
most  complicated  folds  (p.  259),  and  swollen  up  into  the  Coast  Chain, 
and  at  the  same  time  fissures  were  formed  in  the  Cascade  Range,  with 
the  outpouring  of  the  great  lava-flood  of  the  Northwest,  already  spoken 
of  (pp.  210,  262).  Coincidently  with  this  there  was  a  further  letting 
down  of  the  region  of  the  Plains  and  of  the  Basin,  and  a  consequent 
extension  of  the  Pliocene  lakes  in  these  regions,  attended  probably  with 
a  further  rise  of  the  Plateau  region.  During  the  Pliocene,  the  greater 
part  of  the  canon-cutting  of  the  Plateau  region,  and  nearly  all  the  great 
lava-flows  of  the  West,  took  place.  At  the  end  of  the  Tertiary,  these 
lakes  were  in  their  turn  obliterated  by  the  further  upheaval  of  the  con- 
tinent, which  inaugurated  the  Quaternary.  Coincident  with  this  gen- 
eral uplift,  mountain-making  by  crust-block  tilting  occurred  on  a  grand 
scale.  The  Sierra,  the  Wahsatch,  and  the  Basin  Ranges  assumed  their 
present  form  and  height  (p.  265),  and  the  great  north  and  south 
fault-cliffs  of  the  Plateau  region  were  mainly  formed. 

While  this  was  going  on  in  the  western  portion  of  the  continent,  on 
the  southeastern  and  southern  border  the  continent  gained,  by  gradual 
rise,  nearly  all  the  area  shaded  as  Tertiary.  In  this  direction  the  con- 
tinent was  finished  with  the  exception  of  a  large  portion  of  Florida 
and  the  sea-islands  and  alluvial  flats  *  about  the  shores  of  the  Southern 
Atlantic  and  Gulf  States.  These  belong  to  a  still  later  period. 

Thus  we  see  that  from  the  end  of  the  Cretaceous  to  the  end  of  the 
Tertiary  there  was  a  gradual  upheaval  of  the  whole  western  half  of  the 
continent,  by  which  the  axis,  or  lowest  line,  of  the  great  interior  con- 
tinental basin  was  transferred  more  and  more  eastward  to  its  present 
position,  the  Mississippi  River.  Probably  correlative  with  this  up- 
heaval of  the  western  half  of  the  continent  was  the  down-sinking  of 
the  mid-Pacific  bottom,  indicated  by  coral-reefs  (p.  155).  Also  as  a 
consequence  of  the  same  upheaval  the  erosive  power  of  the  rivers  was 
greatly  increased,  and  thus  were  formed  those  deep  canons  in  the 
regions  (New  Mexico,  Colorado,  and  Arizona)  where  the  elevation  was 
greatest.  Thus  the  down-sinking  of  the  mid-Pacific  bottom,  the  bodily 
upheaval  of  the  Pacific  side  of  the  continent,  and  the  down-cutting  of 
the  river-channels  into  those  wonderful  canons,  are  closely  connected 
with  each  other. 

*  In  some  places  about  the  shores  of  the  Gulf,  for  reasons  which  will  be  explained 
hereafter,  the  Quaternary  deposits  are  considerably  elevated  above  the  sea-level. 


QUATERNARY   PERIOD.  545 

SECTION  2. — QUATERNARY  PERIOD. 

Characteristics. — The  chief  characteristic  of  the  Quaternary  is  that 
it  is  a  period  of  great  and  widely-extended  oscillations  of  the  earth's 
crust  in  high-latitude  regions,  attended  with  great  changes  of  climate. 
During  this  period  the  class  of  mammals  seem  to  have  culminated. 
During  this  period  also  man  seems  to  have  appeared  on  the  scene.  We 
do  not  call  it  the  age  of  Man,  however,  because  he  had  not  yet  estab- 
lished his  reign.  His  appearance  here  is  rather  in  accordance  with  the 
law  of  anticipation.  As  already  stated,  the  invertebrate  fauna  was 
almost  identical  with  that  still  living,  but  the  mammalian  fauna  was 
almost  wholly  peculiar,  differing  both  from  the  Tertiary  which  pre- 
ceded and  from  the  present  which  followed  it. 

Subdivisions. — The  Quaternary  period  is  divided  into  three  epochs, 
viz. :  I.  Glacial ;  II.  Champlain ;  III.  Terrace.  These  epochs  are 
characterized  by  the  direction  of  the  crust-movement,  and  of  the  change 
of  climate.  The  Glacial  epoch  is  characterized  by  an  upward  move- 
ment of  the  crust  in  high-latitude  regions,  until  the  continents  in  those 
regions  stood  1,000  to  2,000  feet  above  their  present  height.  Large 
portions  of  these  regions  seem  to  have  been  sheeted  with  ice,  and  an 
arctic  rigor  of  climate  extended  far  into  now  temperate  regions. 

The  Champlain  epoch,  on  the  contrary,  is  characterized  by  a  down- 
ward motion  of  land-surfaces  in  the  same  region  until  the  sea  stood 
relatively  500  to  1,000  feet  above  its  present  level,  covering,  of  course, 
much  that  is  now  land-surface.  It  was,  therefore,  a  period  of  inland 
ice.  Coincident  with  this  sinking  was  a  moderation  of  climate,  and  a 
melting  of  the  ice.  It  was,  therefore,  also  a  period  of  great  lakes  and 
flooded  rivers.  Over  the  inland  seas  and  great  lakes,  masses  of  ice, 
loosened  from  the  ice-sheet  on  their  northern  borders,  floated.  It  was, 
therefore,  also  a  period  of  icebergs. 

The  Terrace  epoch  is  characterized  by  the  gradual  rising  again  to 
the  present  condition  of  the  continents,  and  the  establishment  of  the 
present  condition  of  climate.  It  is,  in  fact,  a  transition  to  the  pres- 
ent era. 

Although  we  call  these  divisions  epochs,  yet  we  must  not  suppose 
that  they  are  equal  in  length  to  the  epochs  of  earlier  times.  As  we 
approach  the  present  time,  and  the  number  and  interest  of  events  in- 
crease, our  divisions  of  time  become  shorter  and  shorter. 

It  is  so  difficult  to  separate  these  epochs  sharply  from  each  other  in 
all  countries,  and  to  synchronize  them,  that  it  seems  best  to  treat  of  the 
whole  Quaternary  period,  taking  up  the  epochs  successively — first  in 
Eastern  North  America,  as  the  type  or  term  of  comparison,  then  of  the 
same  on  the  Pacific  coast,  and  last  of  the  same  in  Europe. 

35 


546  CENOZOIC  ERA— AGE   OF   MAMMALS. 

Quaternary  Period  in  Eastern  North  America. 
I.  Glacial  Epoch. 

The  Materials  —  Drift. — Strewed  all  over  the  northern  part  of 
North  America,  over  hill  and  dale,  over  mountain  and  valley,  covering 
alike,  nearly  all  the  country  rock,  Archsean,  Palaeozoic,  Mesozoic,  and 
Tertiary,  to  a  depth  of  30  to  300  feet,  and  thus  largely  concealing 
them  from  view,  is  found  a  peculiar  surface  soil  or  deposit.  It  con- 
sists of  a  heterogeneous  mixture  of  clay,  sand,  gravel,  pebbles,  sub- 
angular  stones  of  all  sizes,  unsorted,  unstratified,  unfossiliferous.  The 
lowest  part,  lying  in  immediate  contact  with  the  subjacent  country 
rock,  is  often  a  stiff  clay  inclosing  subangular  stones — i.  e.,  rock-frag- 
ments with  the  corners  and  edges  rubbed  off.  This  we  will  call  the 
"  Stony  clay  "  or  "  Bowlder  clay"  It  is  precisely  like  the  ground- 
moraine  of  a  glacier  (p.  55).  Over  this  is  often  found  in  places  a  looser 
material  with  angular  stones,  like  the  top  moraine  of  glaciers.  Lying 
on  the  surface  of  this  drift-soil  are  found  many  bowlders  of  all  sizes, 
often  of  huge  dimensions,  sometimes  even  100  tons  or  more.  The  im- 
bedded subangular  stones  are  usually  marked  with  parallel  scratches 
(Fig.  923),  and  the  large  surface-bowlders  are  usually  angular  and  un- 


FIG.  923.— Subangular  Stone  (after  Geikie). 

scratched.    'The  depth  of  this  material  is  greatest  in  the  valleys  and 
least  on  hill  and  mountain  tops. 

It  is  difficult,  nay,  impossible,  to  give  a  description  of  this  peculiar 
deposit,  which  will  apply  in  all  cases.  Sometimes  scattered  about  ir- 
regularly through  the  unstratified  mass  are  portions  which  are  roughly 
and  irregularly  stratified,  the  laminse  being  often  contorted  in  the 
most  fantastic  way  (Figs.  924-926).  Sometimes  the  true  stony  clay  is 


GLACIAL   EPOCH. 


547 


covered  with  a  more  regularly  stratified  material,  consisting  of  sand  and 
gravel,  apparently  subsequently  deposited  from  water.  This  is  particu- 
larly the  case  in  the  basin  of 
the  Mississippi,  as  e.  g.,  in 
Ohio,  Illinois,  and  Iowa.  It  is 
probable,  however,  that  this  be- 
longs to  the  next  epoch,  Cham- 
plain.  Sometimes  irregular 

mound-like  deposits  are  left  in      pio.  924.— Section  on  Rush  Creek,  near  Mono  Lake, 

the  retreat  of  the  ice.  '  These 

are  called  Jcames,  drumlins,  etc.     The  conditions  under  which  these  are 

formed  are  imperfectly  understood. 


FIG.  925,— Section  of  Orange  Sand,  Missies 


liJgard). 


We^iave  said  that  the  deposit  is  peculiar.     Nothing  resembling  it 
is  founa  anywhere  in  tropical  or  low-latitude  countries.    In  the  South- 


Fio.  926.— Section  of  Orange  Sand,  Mississippi  (after  Hilgard). 

ern  Atlantic  States,  for  instance,  the 'soil  is  mostly  either  the  insoluble 
residue  of  rocks  decomposed  in  situ,  or  else  consists  of  neatly-stratified 
sands  and  clays. 

Drift-material  is  not  usually  represented  on  geological  maps,  since 
it  covers  all  kinds  of  country  rock  ;  or  else  the  c61ors  representing  the 


FIG.  927.— Outcropping— Eroded  Country  Rock  overlaid  by  Drift. 


548 


CENOZOIC  ERA— AGE   OF   MAMMALS. 


various  kinds  and  ages  of  country  rock  are  simply  dotted  to  indicate 
the  presence  of  this  surface-material.  In  sections,  of  course,  it  is  easily 
represented,  as  in  Fig.  927. 

The  Bowlders. — The  most  casual  examination  of  the  great  bowlders 
is  sufficient  in  many  cases  to  show  that  they  do  not  belong  to  the  coun- 
try where  they  now  lie,  for  they  are  of  entirely  different  material  from 
the  country  rock.  For  example,  blocks  of  granite  are  found  where 
there  is  no  granite  within  many  miles,  blocks  of  sandstone  on  a  country 
rock  of  limestone,  or  vice  versa.  In  many  cases  it  is  easy  to  find  the 


FIG.  938.— Bed-rock  scored  with  glacial  marks,  near  Amherst,  Ohio. 

Chamberlin.) 


(From  a  photograph  by 


parent  ledge  from  which  these  great  fragments  were  torn,  and  thus  to 
trace  the  direction  of  their  transportation.  From  many  observations 
of  this  kind  it  has  been  determined  that  in  New.  England  the  bowlders 
have  come  usually  from  the  northivest,  in  Ohio  from  the  north,  and  in 
Iowa  from  the  northeast.  In  other  words,  from  the  highlands  of 
Canada  and  a  ridge  running  thence  northwestward  (Archaean  area),  the 
general  direction  of  travel  has  been  southeast,  south,  and  southwest. 
North  of  the  Archaean  areas  the  travel  was  probably  in  some  cases  even 
northward.  The  distance  carried  may  be  only  a  few  miles,  or  may  be 


GLACIAL  EPOCH. 


549 


ten,  fifty,  one  hundred,  or  even  several  hundred  miles.  In  many  cases 
they  must  have  been  carried  across  valleys  1,000  or  2,000  feet  deep, 
and  lodged  high  up  on  the  mountain  beyond.  In  many  portions 
of  New  England  and  about  Lake  Superior  the  number  of  fragments, 
small  and  great,  is  so  large  as  seriously  to  encumber  the  soil.  Xot  only 
the  large  bowlders,  however,  but  the  whole  mass  of  the  material  we 
have  been  describing,  seem  to  have  been  shifted  to  a  greater  or  less  ex- 
tent. It  is  for  this  reason  that  the  material  has  been  called  Drift. 

Surface-Rock  underlying1  Drift. — On  removing  the  drift-covering 
the  underlying  rock  is  every  where  polished  and  planed  and  scored  with 
parallel  lines  (Fig.  928),  and  moutonne,  precisely  like  rocks  over  which 
a  glacier  has  passed.  We  will,  therefore,  call  this  surface-appearance 
" glaciation"  We  reproduce  here  from  page  56  the  roches  moutonnees 
of  an  ancient  glacier  in  Colorado  (Fig.  929).  Examinations  of  the 


FIG.  929.— Roches  Moutonnees  of  an  Ancient  Glacier,  Colorado  (after  Hayden). 

• 

scorings  show  that  they  often  pass  straight  up  inclines  for  considerable 
distances,  i.  e.,  up  one  side  of  a  hill,  over  the  top,  and  down  the  other 
side.  Their  direction  is  uninfluenced  by  smaller  inequalities  of  surface, 
though  they  are  thus  influenced  by  the  great  valleys  and  mountain- 
ridges. 

The  general  direction  of  the  scorings  corresponds  with  that  of 
transportation  of  the  bowlders,  showing  that  they  are  due  to  the  same 
cause.  Perfect  soil  on  perfect  sound  rock  always  shows  that  the  soil 
has  not  been  formed  in  situ,  but  has  been  shifted :  the  polishing,  plan- 


550 


CENOZOIC   ERA— AGE   OF  MAMMALS. 


ing,  scoring,  etc.,  of  the  rock  show  that  the  agent  of  the  shifting  has 
been  ice. 

Extent. — The  general  extent  of  these  more  conspicuous  and  char- 
acteristic phenomena,  viz.,  the  glaciation,  the  stony  clay,  and  the  great 
bowlders,  is  down  to  about  40°  north  latitude.  The  line  of  southern 
limit  cuts  the  Atlantic  coast  about.  40°,  near  New  York ;  it  then  bends 
a  little  southward  to  37°  30'  in  Southern  Illinois,  and  then  turns  a  little 
northward  t again  as  it  passes  west,  and  may  be  traced  northwestward 
nearly  to  Montana  (Fig.  931),  and  reappears  on  the  Pacific  slope  in  the 


FIG.  930.— Moraines  of  Grape  Creek,  Sangre  del  Cristo  Mountains,  Colorado  (after  Stevenson). 

southern  portion  of  British  Columbia  (Dawson).  Beyond  this  the 
characteristic  phenomena  mentioned  above  are  not  found,  but  in  the 
valley  of  the  Mississippi,  and  on  each  side  to  a  considerable  distance, 
a  superficial  gravel  and  pebble  deposit,  containing  northern  bowlders — 
called  by  Prof.  Hilgard  "  Orange  Sand  " — extends  to  the  shores  of  the 
Gulf.  Evidences  of  local  glaciers  in  the  form  of  moraines  are  found 
abundantly  in  the  Colorado  Mountains  (Fig.  930). 

Marine  Deposits. — Along  the  Atlantic  coasts  we  find  no  marine 
deposits  of  this  time,  for  the  obvious  reason  that  the  continent  was  then 
more  elevated  than  now ;  whatever  marine  deposits  were  then  formed 
are  now  covered  by  the  sea. 


THEORY  OF  THE  ORIGIN  OF  THE  DRIFT.  551 

TJieory  of  the  Origin  of  the  Drift. 

When  the  phenomena  of  the  Drift  were  first  observed,  they  were 
supposed  to  indicate  the  agency  of  powerful  currents,  such  as  could  be 
produced  only  by  the  most  violent  and  instantaneous  convulsions.  A 
sudden  upheaval  of  the  ocean-bed  in  northern  regions  was  supposed  to 
have  precipitated  the  sea  upon  the  land,  as  a  huge  wave  of  translation, 
which  swept  from  north  toward  the  south,  carrying  death  and  ruin  in 
its  course.  Hence  the  deposit  was  often  called  Diluvium  (deluge- 
deposit).  Now,  however,  they  are  universally  ascribed  to  the  agency  of 
ice  acting  slowly  through  great  periods  of  time.  Hence  the  name 
Glacial  epoch. 

As  to  the  manner  in  which  the  ice  acted,  however,  opinions  have 
been  more  or  less  divided,  some  attributing  the  phenomena  to  the  agency 
of  land-ice — glaciers — others  to  that  of  drifting  icebergs.  According 
to  the  one,  the  land  during  this  epoch  was  greatly  raised  and  covered 
with  glaciers  ;  according  to  the  other,  the  same  area  was  sunk  several 
thousand  feet  and  swept  by  drifting  icebergs,  carried  southward  by  cur- 
rents, and  dropping  their  load  of  earth  and  stones.  The  one  is  called 
the  glacier  theory,  the  other  the  iceberg  theory. 

It  is  probable  that  both  these  agencies  were  at  work,  either  at  the 
same  time  or  consecutively ;  but  the  decided  tendency  of  science  is 
toward  the  recognition  of  glaciers  as  the  principal  agent  during  this 
earliest  epoch  of  the  Quaternary.  The  more  the  phenomena  are 
studied,  and  the  more  glaciers  are  studied,  especially  in  polar  regions, 
the  larger  is  the  share  attributed  to  this  agency.  We  will  not  discuss 
this  question,  but  simply  give  the  present  condition  of  science  on  the 
subject. 

Statement  of  the  most  Probable  View. — The  most  probable  view 
for  America,  and  also  for  other  countries,  is,  that  the  Drift,  or  at  least 
the  most  characteristic  phenomena  of  the  Drift,  viz.,  the  glaciation,  the 
unsorted  bowlder -clay,  and  in  many  cases  also  the  great  traveled 
bowlders,  are  due  to  the  action  of  glaciers.  They  are  therefore  a  land- 
deposit,  and  not  a  sub-aqueous  deposit.  For  general  proof  of  this,  let 
any  one  study  the  phenomena  of  living  glaciers,  in  the  Alps  and  else- 
where ;  then  let  him  study  the  appearances  left  by  the  recently  dead 
glaciers  of  the  Sierra ;  and  then  let  him  study  the  phenomena  of  the 
Drift,  especially  the  stony  clay  and  the  underlying  glaciated  surfaces. 
It  will  be  impossible  for  him  to  come  to  any  other  conclusion  than  that 
the  same  agent  has  been  at  work  in  all  these.  In  some  cases  still 
more  conclusive  evidence  is  found  in  the  existence  of  distinct  terminal 
moraines. 

Objections  answered. — Many  objections  have  been  brought  against 
this  view,  which  may  be  compendiously  stated  as  follows :  1.  In  glacial 


552  CENOZOIC  ERA— AGE   OF   MAMMALS. 

regions,  like  Switzerland,  the  Himalayas,  etc.,  the  glaciers  run  in  all 
directions ;  but  the  Drift  was  carried  over  wide  areas,  in  a  general 
direction.  Such  a  general  direction  is  easily  accounted  for  by  the 
action  of  icebergs  carried  by  marine  currents.  2.  The  agent  of  the 
Drift  seems  to  have  been  often  uninfluenced  by  the  direction  of  valleys 
and  ridges  even  of  considerable  size ;  thus,  for  instance,  bowlders  are 
carried  across  valleys  500  or  1,000  feet  deep,  and  lodged  as  high  up  on 
the  mountain-slope  on  the  other  side.  This  is  perfectly  consistent 
with  the  action  of  icebergs  drifting  over  an  uneven  sea-bottom,  but  in- 
consistent with  our  usual  notions  of  glacial  action.  3.  The  great  dis- 
tance carried,  sometimes  one  hundred  miles  or  more,  is  precisely  what 
we  might  expect  of  icebergs,  but  difficult  to  reconcile  with  our  usual 
notions  of  glaciers.  4.  Alpine  glaciers  will  not  move  on  a  slope  of  less 
than  2°  or  3°,  but  such  a  slope,  carried  several  hundred  miles,  would 
produce  an  incredible  elevation  of  land.  A  slope  of  2-J-0  for  200  miles 
would  produce  an  elevation  of  nearly  nine  miles  ! 

These  were  unanswerable  objections  so  long  as  our  ideas  of  glaciers 
were  confined  to  those  of  temperate  climates ;  but  they  all  find  their 
complete  answer  in  the  phenomena  of  the  polar  ice-sheet.  Greenland  is 
1,200  miles  long  and  400  or  500  miles  wide.  This  whole  area  of  over  a 
half -million  of  square  miles  is  covered  3,000  to  6,000  feet  deep  with 
ice.*  This  ice-mantle  moves  en  masse  seaward,  molding  itself  on  the 
surface  inequalities  of  the  country,  and  molding  that  surface  beneath 
itself,  producing  universal  glaciation,  and  only  separating  into  distinct 
glaciers  at  its  margin.  In  antarctic  regions,  the  general  ice-sheet  is 
even  still  more  extensive  and  thick.  Now,  it  is  to  such  an  ice-mantle 
that  the  Drift  is  to  be  ascribed,  for  it  moves  irrespective  of  smaller  val- 
ley's,  in  one  general  direction  over  great  areas,  to  great  distances,  and 
over  a  slope  of  only  1°  or  even  -J°. 

Probable  Condition  of  Things  in  the  Eastern  part  of  the  Continent 
during  the  Glacial  Epoch. — The  continental  elevation,  which  com- 
menced in  the  Pliocene,  culminated  during  this  time.  In  the  northern 
part  of  the  continent  it  probably  reached  2,000  to  3,000  feet  above  its 
present  level.  The  shore-line  was  at  least  as  far  out  as  the  submerged 
continental  margin,  and  all  the  coast  islands  of  this  part  were  added  to 
the  continent.  The  evidence  of  this  is  found  in  deep  submarine  chan- 
nels off  the  mouths  of  all  the  great  rivers,  such  as  the  St.  Lawrence, 
the  Hudson,  the  Delaware,  etc.,  cutting  through  the  submerged  conti- 
nental border,  and  evidently  formed  by  erosion  during  the  Tertiary. 
The  axis  of  elevation  was  the  Canadian  Archaean  highlands,  and  thence 
-it  became  less  both  northward  and  southward,  but  undoubtedly  ex- 
tended to  the  shores  of  the  Gulf.  Coincidently  with  this  elevation, 

*  Nansen,  Nature,  vol.  xl,  p.  210,  1889. 


/  J 

THEORY   OF  THE   ORIGIN   OF   THE  DRIFT.  553 

and  presumably  as  its  effect,  the  whole  northern  part  of  the  continent 
was  covered  with  a  general  ice-sheet,  10,000  feet  thick  over  Canada, 
6,000  feet  over  New  England,  and  thinning  southward.  From  this 
Archaean  area  as  a  radiant  the  ice  moved  with  slow,  glacial  motion 
southeastward,  southward,  and  southwestward  over  New  England,  New 
York,  Ohio,  Illinois,  Iowa,  and  Dakota,  regardless  of  all  but  the  great- 
est inequalities — filling  the  valleys,  sweeping  over  the  mountain-tops, 
and  glaciating  the  whole  surface  in  its  course.  Northward  the  sheet 
perhaps  extended  to  the  poles,  although  it  was  thickest  on  the  Ar- 
chaean axis ;  for  there  are  evidences  of  a  northward  movement  from 
this  axis  in  some  places.  Its  eastward  limit  was  beyond  the  present 
coast-line;  its  southern  limit  about  38°  to  40°  north  latitude  (Fig. 
931).  Even  farther  south,  high  mountain-ranges,  like  the  Colorado 
mountains,  were  ice-covered,  and  great  glaciers  streamed  down  their 
flanks  and  left  their  moraines'  (Fig.  930).  Along  the  New  England 
coast  possibly  the  ice-sheet  in  many  places  ran  into  the  sea  and  pro- 
duced icebergs,  but  wherever  the  limit  was  on  land,  as  in  the  interior 
of  the  continent  and  in  some  places  even  on  the  eastern  coast,  it  doubt- 
less formed  a  terminal  moraine,  though  this  has  been  mostly  washed 
away  by  subsequent  erosion. 

Terminal  Moraines  of  the  Ice-Sheet. — We  have  already  seen  that  the 
limit  of  the  ice-sheet — where  this  was  on  land — was  probably  marked 
by  a  moraine.  Fragments  of  such  a  moraine  have  been  found  along 
this  limit,  especially  in  its  eastern  part.  Westward  it  has  been  mostly 
washed  away  by  the  floods  issuing  from  the  melting  and  retreat- 
ing ice-sheet.  The  extreme  limit,  therefore,  in  most  places  is  best 
shown  by  the  presence  of  glaciation.  In  one  way  or  another  it  may 
be  traced  throughout  its  whole  extent.  Its  most  northeastern  end  is 
found  at  Cape  Cod;  thence  it  goes  southwest  through  Nantucket, 
Martha's  Vineyard,  and  Long  Island ;  thence  through  Northern  New 
Jersey,  Northeastern  Pennsylvania,  touching  the  southern  border  of  New 
York ;  thence  southwest  through  Ohio  to  the  Ohio  River,  whose  north- 
ern border  it  follows  to  the  Mississippi ;  thence  crossing  the  Mississippi 
it  follows  the  Missouri  on  its  south  side,  and  so  northwestward  through 
Montana  and  into  British  America.  This  may  be  called  the  ice-sheet 
boundary. 

After  reaching  this  extreme  limit,  .the  ice-sheet  retreated  to,  or 
probably  beyond,  the  Great  Lakes,  and  then  advanced  again,  but  not  so 
far  as  before.  This  second  and  more  recent  advance  is  marked  by  a 
very  distinct  and  nearly  continuous  moraine  of  irregular,  deeply-lobed 
outline.  In  its  eastern  part  this  second  ice-sheet  moraine  is  coincident, 
with,  or  undistinguishable  from,  the  first  already  described.  But  in 
Ohio  the  two  moraines  part  company ;  the  second  moraine,  instead  of 
passing  southward  to  the  Ohio  River,  sweeps  in  a  series  of  looping 


554 


CENOZOIC   ERA— AGE   OF   MAMMALS. 


curves  about  the  Great  Lakes  and  through  Iowa,  and  thence  northwest- 
ward on  the  north  side  of  the  Missouri,  through  Dakota,  into  British 
America.  The  discovery  of  this  moraine,  which  we  owe  chiefly  to 
Chamberlin  and  Upham,  must  be  regarded  as  a  complete  demonstra- 
tion of  the  existence  of  the  ice-sheet.  In  the  map  (Fig.  931)  the 


Ice-sheet 
Boundary. 

B  Second  Ice- 
sheet  Moraine. 
r~/l  Direction  of 
L*_J    Strife, 
nr— 1  Boundary  of 
I  ''•'  J    Lake  Agassiz. 
Appalachian 
Range. 


FIG.  931.— Map  showing  the  Extreme  Boundary  of  the  Ice-sheet,  the  Second  Ice-sheet  Moraine,  and 
the  Outlines  of  Lake  Agassiz. 

strong  line  shows  the  extreme  limit  of  the  first  advance,  the  dotted  lines 
the  moraine  formed  by  the  second  advance  of  the  ice-sheet.  In  its  last 
retreat  many  subordinate  moraines  were  left  one  behind  another.  We 
have  represented  mainly  the  most  advanced. 

Thus  we  have  clear  evidence  of  a  second  glacial  and  an  interglacial 
epoch.  That  this  interglacial  epoch  was  of  considerable  length  is 
shown  by  the  existence  of  a  forest-bed  between  the  two  glacial  tills 
(Newberry).  Again,  since  melting  and  retreat  of  the  ice- sheet  must 


CHAMPLAIN   EPOCH.  555 

produce  flooding,  it  is  probable  that  there  were  two  flooded  periods. 
These  have  doubtless  been  often  confounded  with  one  another. 

//.  Champlain  Epoch. 

During  the  Glacial  epoch,  as  just  seen,  the  whole  northern  portion 
of  the  continent  was  elevated  1,000  to  2,000  feet  above  the  present  con- 
dition ;  the  northern  ice-sheet  had  advanced  southward  to  40°  latitude, 
with  still  farther  southward  projections  favored  by  local  conditions ; 
and  an  arctic  rigor  of  climate  prevailed  over  the  United  States  even  to 
the  shores  of  the  Gulf.  At  the  end  of  this  epoch  an  opposite  or  down- 
ward movement  of  land-surface  over  the  same  region,  probably  in- 
creased by  the  weight  of  accumulating  ice,  commenced  and  continued 
until  a  depression  of  500  to  1,000  feet  below  the  present  level  was  at- 
tained. This  downward  movement  marks  the  beginning  of  the  Cham- 
plain  epoch.  As  a  necessary  consequence,  large  portions  of  the  now 
land  were  submerged ;  it  was  therefore  a  time  of  inland  seas.  Another 
result,  or  at  least  a  concomitant,  was  a  moderation  of  the  climate,  a 
melting  of  the  glaciers,  and  a  final  retreat  of  the  ice-sheet  northward. 
It  was  therefore  a  time  of  flooded  lakes  and  rivers.  Lastly,  over  these 
inland  seas  and  great  lakes  loosened  masses  of  ice  floated  as  icebergs. 
It  was  therefore  pre-eminently  a  time  of  iceberg  action. 

Evidences  of  Subsidence. — The  evidences  of  the  condition  of  things 
described  above  are  found  in  old  sea-margins,  old  lake-margins,  old 
river-terraces,  and  old.  flood-plain  deposits. 

1.  Sea-Margins. — Old  sea-margins,  containing  shells  and  other  re- 
mains of  living  species,  are  found  all  along  the  Northern  Atlantic  coast, 
becoming  higher  as  we  pass  northward.  In  Southern  New  England  the 
highest  beaches  are  40  to  50  feet ;  about  Boston  they  are  75  to  100 
feet ;  in  Maine  they  are  200  feet  and  upward ;  on  the  Gulf  of  St.  Law- 
rence they  are  470  feet ;  in  Labrador  1,500  feet  (Upham).  In  arctic 
regions  they  are  in  some  places  1,000  feet  (Dana).  The  beaches  may  be 
traced  up  both  sides  of  the  St.  Lawrence  River,  and  thence  around  Lake 
Champlain,  where  the  highest  is  393  feet  above  tide-level.*  Upon  the 
beaches  about  Lake  -Champlain  have  been  found  abundance  of  marine 
shells,  and  also  the  skeleton  of  a  stranded  whale.  Evidently  there  was 
here  a  great  inland  sea  connected  with  the  ocean  through  the  Gulf  of 
St.  Lawrence  ;  and  over  this  sea  icebergs  must  have  floated.  This  con- 
dition of  things  has  given  name  to  the  epoch.  In  the  subsequent  re- 
elevation  of  the  continent,  this  salt  lake  (as  it  must  have  been  at  first) 
was  gradually  rinsed  out  and  freshened  by  river-water  discharged 
through  the  lake  and  into  the  St.  Lawrence  River,  as  already  explained 
on  a  previous  page  (p.  31.)  All  the  crust-oscillations  characteristic  of 

*  Dana,  Manual,  p.  550. 


556  CENOZOIC  ERA— AGE   OF  MAMMALS. 

this  period  are  detectable,  also  along  the  South  Atlantic  and  Gulf  coast. 
During  the  early  Quaternary  (Glacial  epoch)  the  continental  elevation 
produced  torrential  currents  which  formed  the  coarse  pebble  deposit 
of  the  Gulf  States,  called  Orange  sand  by  Hilgard.  During  the  period 
of  subsidence,  the  coastal  plains  were  again  covered  by  the  sea,  and  the 
shore  was  again  at  the  fall-line.  The  deposits  of  this  time  form  the 
Columbian  formation  of  McGee.  Finally,  from  this  subsided  condition 
the  land  rose  to  its  present  level  during  the  Terrace. 

2.  Flooded  Lakes. — All  the  lakes  in  the  region  affected  by  drift  show 
unmistakable  evidences  of  a  far  more  extended  and  higher  condition 
of  the  waters  than  now  exists.  About  all  these  lakes  is  found  a  suc- 
cession of  terraces  or  old  lake-margins.  The  highest  of  these  marks 
the  highest  water-level,  and  is  the  oldest ;  the  lower  ones  mark  succes- 
sive steps  in  the  draining  away  or  drying  away  of  the  waters. 

For  example,  about  Lake  Ontario  successive  margins  are  found  up 
to  500  feet  above  the  present  lake-level ;  about  Lake  Erie  up  to  250 
feet ;  about  Lake  Superior,  up  to  330  feet ;  and  similar  margins  are 
found  about  Lakes  Michigan  and  Huron.  It  seems  not  improbable 
that  the  retreating  ice- front  acted  as  a  barrier,  against  which  accumu- 
lating water  formed  one  or  more  enormous  lakes,  over  which  floated 
icebergs  loosened  from  the  Canadian  ice-foot.  These  lakes  drained 
southward  into  the  Ohio  and  Mississippi  until  the  barrier  was  removed 
by  the  final  retreat  of  the  ice-sheet ;  and  then  northeastward,  as  now, 
through  the  St.  Lawrence. 

LakeAgassiz. — Another  great  glacial  lake  in  the  region  of  Lake 
Winnipeg,  probably  formed  in  the  same  way,  was  first  discovered  and 
figured  by  General  (then  Lieutenant)  Warren,  but  recently  traced  out 
with  accuracy  by  Upham.  The  retreating  ice-front  acted  as  a  dam, 
against  which  the  waters  of  the  melting  ice-sheet,  together  with  the 
natural  drainage  of  this  region,  accumulated  to  form  a  lake  of  enormous 
dimensions — greater  than  all  the  present  Great  Lakes  put  together. 
This  great  glacial  lake  drained  southward  through  the  Minnesota  into 
the  Mississippi.  With  the  final  retreat  of  the  ice-sheet,  the  drainage 
was  reversed,  and  its  dwindled  remains — Lake  Winnipeg — drained,  as 
now  northward,  into  Hudson  Bay.  The  outlines  of  this  ancient  lake 
have  been  accurately  mapped  by  means  of  its  still  existing  terraces  and 
it  has  been  named  Lake  Agassiz,  in  honor  of  the  great  champion  of 
land-ice  as  the  cause  of  the  Drift.  In  map,  Fig.  931,  we  have  given  the 
outlines,  taken  from  Upham,  of  the  southern  portion  of  this  ancient 
lake.  It  has  been  traced  by  Tyrrell  150  to  170  miles  northward  in  Can- 
ada,* and  more  recently  its  whole  outline  has  been  mapped  by  Upham.  f 

*  Bulletin  of  the  American  Geological  Society,  vol.  i,  p.  404. 
f  Geological  Survey  of  Canada,  vol.  iv,  E,  p.  10,  1890. 


CIIAMPLAIX   EPOCH.  557 

Both  the  elevation  of  the  previous  epoch  and  the  subsidence  of  this 
seem  to  have  been  greater  along  the  axis  of  the  continent,  the  valley  of 
the  Mississippi,  than  on  the  coasts.  Hilgard  finds  evidence  in  the 
Orange  sand-deposit,  and  in  the  thickness  of  the  subsequent  Champlain 
deposit,  of  an  elevation  of  450  feet  above  the  present  level,  and  a  depres- 
sion of  450  feet  (for  this  is  the  maximum  elevation  of  the  Champlain 
deposit  above  the  same  level),  or  an  oscillation  of  900  feet  in  Louisiana. 
The  submarine  channel  of  the  Mississippi,  recently  found  beyond  the 
limits  of  the  delta  deposit,  show  an  even  much  higher  elevation  in  the 
Gulf  region  (Spencer).  Farther  north  it  is  probably  still  greater. 

3.  River  Terraces  and  Old  Flood-Plain  Deposits. — Nearly  all  the 
rivers  in  the  eastern  portion  of  the  continent,  over  the  Drift  region,  are 
bordered  with  high  terraces,  which  have  been  cut  wholly  out  of  an  old 
flood-plain  deposit  belonging  to  the  Cliamplain  epoch.  In  fact,  these 
rivers  show  first  an  elevation,  then  a  depression,  and  finally  a  partial  re- 
elevation  ;  in  other  words,  all  the  oscillations  of  the  Quaternary  period 
are  recorded  by  them. 

An  examination  of  the  rivers  north  of  the  fortieth  parallel  shows : 
1.  An  old  river-bed  far  deeper  and  broader  than  the  present ;  2.  This 
deep  and  broad  river-bed  is  filled  up,  often  several  hundred  feet  deep, 
by  old  river-deposit ;  3.  Into  this  old  river-deposit  the  shrunken  stream 
is  again  cutting,  but  is  still  far  above  the  bottom  of  the  old  river-bed. 
This  cutting  into  the  old  river-deposit  produces  bluffs  and  terraces  on 
each  side.  It  is  evident  that  the  great  river-bed  was  gouged  out  during 
late  Tertiary  and  early  Glacial  epochs ;  the  filling  up  took  place  during 
the  Champlain,  and  the  cutting  and  terracing  during  the  Terrace 
epoch.  Some  of  these  old  river-channels,  as,  for  example,  that  of  the 
St.  Lawrence,  the  Hudson,  and  the  Delaware,  may  be  traced  far  out  to 
sea,  to  the  sunken  borders  of  the  glacial  continent. 

Fig.  932  is  an  ideal  section  across  a  river-bed  in  the  Drift  region, 
in  which  ~b  ~b  is  the  old  river-bed,  scooped  out  during  the  epoch  of  ele- 


FIG.  932.— Ideal  Section  acrops  a  River-bed  in  Drift  Region:  b  b  b,  old  river-bed;  K,  the  present 
river;  1 1,  upper  or  older  terraces;  I' t',  lower  terraces. 

vation ;  the  dotted  line  represents  the  highest  level  to  which  the  old 
river-deposit  accumulated,  and  the  shaded  portion  that  part  of  such 
deposit  which  still  remains.  The  upper  terraces,  1 1,  are  of  course  the 
oldest,  the  lower  ones  being  made  as  the  shrunken  stream  cut  deeper 
and  deeper. 


558  CENOZOIC   ERA— AGE   OF   MAMMALS. 

These  phenomena  are  shown  in  all  the  river-beds  of  the  Drift  region, 
but  especially  by  those  of  the  Mississippi  basin.  Sometimes  there  is 
only  one  terrace  or  bluff ;  sometimes  there  are  several,  on  each  side. 
The  Connecticut  River  is  a  good  example  of  the  latter,  the  Mississippi 
River  of  the  former. 

The  Connecticut  River  is  bordered  on  each  side  by  a  succession  of 
terraces  rising  one  above  and  beyond  the  other,  composed  wholly  of 
old  river-deposit.  Beyond  this,  of  course,  is  the  country  rock  of  Jura- 
Trias  sandstone,  covered  more  or  less  with  drift. 

The  Mississippi  River  is  bordered  on  each  side  by  its  present  flood- 
plain  deposit,  or  river-swamps.  This,  as  already  said  (p.  25),  extends 
from  the  mouth  of  the  Ohio  River  to  the  head  of  the  delta,  a  distance 
of  500  miles,  and  has  an  average  width  of  30  miles.  This,  its  present 
flood-plain  deposit,  is  limited  on  the  eastern  side  by  bluffs  in  some 
places  200  to  400  feet  high,  composed  of  Tertiary  strata,  capped  with 
an  old  river-silt,  or  Loess,  50  to  70  feet  thick,  and  this,  again,  covered 
by  a  yellow  loam,  which  extends  beyond  the  limits  of  the  Loess.  A 
layer  of  Orange  sand  separates  the  Loess  from  the  Tertiary.  Patches 
of  the  Loess  or  bluff-deposit  are  found  also  on  the  western  side,  show- 
ing that  the  old  flood-plain  extended  beyond  the  present  flood-plain 
on  both  sides ;  but  on  the  west  side  it  has  been  mostly  removed  by  sub- 
sequent erosion.  Also  similar  deposits,  often  of  great  extent,  form 
banks  on  each  side  of  all  the  great  tributaries  of  the  Mississippi.  Be- 
neath the  present  river  swamp-deposit  is  found,  by  borings,  a  deposit 
belonging,  like  the  Loess,  to  the  Champlain  epoch,  but  to  an  earlier 
period,  probably  an  estuary  deposit,  and  called  by  Hilgard  "  Port  Hud- 
son" varying  in  thickness  from  thirty  feet  at  Memphis  to  several  hun- 
dred feet  in  the  delta.  Beneath  this  is  first  the  Orange  sand  and  then 
the  Tertiary. 

All  these  facts  are  represented  in  the  ideal  section  of  the  river  and 
the  strata  in  its  vicinity,  given  below,  constructed  from  the  investiga- 


FIG.  933.— Ideal  Section  across  Mississippi  below  Vicksbnrg:  OS,  Orange  sand;  PH.  Port  Hudson, 
estuary  deposit,  Champlain;  Is,  Loess  or  old  flood-plain  deposit,  Champlain;  I,  loam  covering 
the  Loess,  but  more  extensive;  rs,  river-swamp  deposit,  moderate. 

tions  of  Prof.  Hilgard.  It  is  evident  that  a  great  trough  was  hollowed 
out  in  the  Tertiary  strata  during  the  late  Tertiary  and  early  Glacial 
epoch,  filled  with  deposit  to  the  level  1 1  during  the  Champlain,  and 
again  partly  cut  out  during  the  Terrace. 


CIIAMPLAIN   EPOCH.  559 

The  cause  of  the  flooded  condition  of  the  rivers  and  lakes  was  partly 
the  depression  of  the  land,  by  which  the  sea  entered  into  the  old  glacial 
beds,  forming  estuaries ;  partly  the  smaller  angle  of  slope  of  the  rivers, 
by  reason  of  which  the  waters  in  their  lower  parts  ran  off  less  rapidly, 
and  therefore  were  more  swollen,  and  therefore  also  deposited  more 
sediment ;  and  partly  the  greater  abundance  of  the  water-supply,  from 
the  melting  of  the  glaciers.  The  mud-supply  also  was  then  very  great, 
as  shown  by  the  immense  deposit,  and  also  by  the  cross-lamination  (p. 
17-4)  so  common  in  these  deposits. 

Origin  of  the  Loess. — Over  large  areas  bordering  the  Mississippi 
and  its  tributaries,  and  forming  the  conspicuous  bluffs  of  these  rivers, 
there  is  found  a  peculiar  deposit  of  very  fine,  even-grained,  and  usually 
unstratified  material,  remarkable  for  forming  by  river-erosion  perpen- 
dicular walls — although  soft  enough  to  be  easily  spaded.  It  is  usually 
destitute  of  organic  remains,  but  when  these  are  found  they  consist 
of  fresh-water  shells,  and  especially  of  land-shells.  When  fresh- water 
shells  are  found,  the  material  is  usually  obscurely  stratified.  Similar 
bluff-materials  are  found  bordering  nearly  all  the  European  rivers,  such 
as  the  Rhine  and  Danube,  and  is  there  called  Loess,  and  referred  to  the 
Champlain  epoch. 

A  somewhat  similar  material,  however,  is  found  also  spread  almost 
evenly  over  wide  areas  nearly  everywhere,  especially  in  arid  regions,  and 
having  no  obvious  connection  with  any  rivers.  Such  is  especially  the 
case  in  Northern  China,  where  Richthofen  finds  it  covering  thousands 
of  square  miles,  and  in  places  one  thousand  or  more  feet  thick.  Russell 
also  finds  a  somewhat  similar  unstratified  deposit  covering  unusually 
large  areas  of  the  Basin  region,  and  sometimes  locally  called  ".adobe." 

There  has  been  much  discussion  about  the  origin  of  these  deposits. 
The  Loess  of  the  Mississippi  and  its  tributaries,  as  also  the  European 
rivers,  was  probably  deposited  in  the  flooded  lakes  and  in  the  slack- 
ened waters  of  the  flooded  rivers  of  the  Champlain  epoch.  It  is  poor 
in  fossils,'  because  the  waters  were  ice-cold.  It  is  unstratified,  because 
the  waters  were  overloaded  with  the  very  finely  triturated  material  left 
by  the  retreating  ice-sheet. 

The  Loess  of  Northern  China,  Richthofen  thinks,  is  an  sEolian  de- 
posit— i.  e.,  a  deposit  of  wind-borne  dust  from  the  arid  regions  to  the 
northwest.*  The  unstratified  superficial  soil  of  the  Basin  region,  Rus- 
sell thinks,  is  due  partly  to  wind-borne  dust,  but  mainly  to  rain-wash 
— i.  e.,  to  the  semi-liquid,  creamy  mud  washed  down  the  bare  slopes  by 
heavy  rains ;  for  in  these  arid  regions,  although  rain  is  rare,  it  falls  in 
torrents. f  The  unstratified  soil,  often  called  Loess,  covering  the  hilly 

*  American  Journal  of  Science,  vol.  xiv,  p.  487,  1877. 
f  Russell,  Geological  Magazine,  vol.  vi,  p.  289,  1889. 


560  CENOZOIC  ERA— AGE   OF   MAMMALS. 

country  at  the  base  of  the  Alps,  is  attributed  by  Sacco  to  rain-wash  of 
bare  soil  recently  left  by  the  retreating  ice.* 

It  is  probable,  therefore,  that  several  kinds  of  deposit,  having  a 
superficial  resemblance,  have  been  confounded  under  the  common  term 
of  Loess,  and  that  more  observation  is  necessary  to  clear  up  the  subject. 

///.  Terrace  Epoch. 

At  the  end  of  the '  epoch  of  subsidence,  when  the  condition  of  sea 
and  lakes  and  rivers  was  what  we  have  described,  there  commenced  a 
movement  again  in  an  opposite  direction,  by  which  the  lands  were  slowly 
brought  upward  to  their  present  condition — a  condition,  however,  far 
less  elevated  than  during  the  Glacial  epoch. 

Evidences. — 1.  Sea. — The  re-elevation  was  not  perfectly  steady  and 
uniform,  but  stopped,  from  time  to  time,  sufficiently  long  for  the  sea 
to  make  distinct  beaches.  Below  the  highest  beach,  which  marks  the 
maximum  depression  of  the  Champlain  epoch,  and  which  has  already 
been  described,  several  other  beaches  are  traceable,  which  evidently 
mark  the  successive  steps  of  re-elevation. 

2.  Lakes. — Also,  the  re-elevation  of  the  land  would  bring  down  the 
level  of  the  lakes,  partly  by  change  of  climate  diminishing  the  water- 
supply,  and  partly  by  increasing  the  slope,  and  thereby  increasing  the 
erosive  power,  of  the  discharge-rivers,  and  thus  draining  off  the  lake- 
waters.  This  is  well  shown  on  the  Canadian  lakes,  where,  in  addition 
to  the  'highest  terrace,  already  mentioned,  which  marks  the  highest 
flood-level  of  the  Champlain  epoch,  are  found  several  lower  terraces, 
which  mark  the  successive  stages  of  the  subsequent  depression  of  the 
lake-surface.  These  distinct  beaches  would  seem  to  indicate  that  the 
rate  of  draining  away  and  letting  down  of  the  water  was  not  uniform, 
but  had  periods  of  greater  and  periods  of  less  rapidity. 

History  of  the  Great  Lakes. — The  origin  of  these  lake-basins  is  still 
doubtful.  They  probably  did  not  exist  in  the  Tertiary  period,  but  in 
their  place  was  a  great  depression  draining  northeastward.  During 
the  Glacial  epoch  this  depressed  area  was  swept  out  and  perhaps  deep- 
ened by  the  advancing  ice-sheet.  The  irregular  gouging  of  the  ice- 
sheet,  and  especially  the  irregular  choking  of  the  drainage  area  by 
debris  left  by  its  retreat,  probably  gave  origin  to  the  lakes.  In  the 
early  Champlain,  as  already  said,  they  were  all  united  into  one  im- 
mense sheet  draining  southward  through  the  Ohio  and  Mississippi, 
the  natural  drainage  northeastward  being  prevented  by  the  ice-foot. 
Then,  by  the  retreat  of  the  ice  northward,  and  the  accompanying  con- 
tinental elevation,  this  one  lake  was  broken  up  into  several,  which 
found  an  outlet  eastward  through  the  Mohawk  Valley  and  Hudson 

*  Archives  des  Sciences,  1889,  vol.  xxi,  p.  355. 


TERRACE  EPOCH.  561 

River  into  the  Atlantic.  Finally,  by  further  retreat  of  the  ice-foot, 
they  drained  northeastward,  as  now,  through  the  St.  Lawrence  River. 

3.  Rivers. — It  is  hardly  necessary  to  say  that  the  re-elevation  would 
lay  bare  the  old  flood  and  estuary  deposits  of  the  rivers,  and  the  rivers 
would  immediately  commence  cutting  into  these  deposits,  forming  ter- 
races and  bluffs,  in  number  and  height  depending  upon  the  depth  of 
the  cutting.  The  Connecticut  River  has  made  many  of  these  terraces, 
the  highest,  of  course,  being  the  oldest.  The  Mississippi  has  apparently 
made  but  one,  but  this  one  is  very  high  (Fig.  933).  The  highest  point 
of  this  Champlain  deposit,  according  to  Hilgard,  is  at  least  450  feet 
above  tide-level,  showing  a  re-elevation  and  a  cutting  to  that  extent 
during  the  Terrace  epoch. 

History  of  the  Mississippi  River. — It  may  be  interesting  to  stop  a 
moment,  and  trace,  briefly,  the  history  of  this  great  river.  During  the 
Cretaceous  period,  the  Ohio  probably  ran  into  the  embayment  of  the 
Gulf,  represented  in  Fig.  755  (p.  470) ;  but  the  Mississippi  probably 
did  not  yet  exist.  The  drainage  of  all  that  part  of  the  continent  was, 
doubtless,  into  the  great  interior  Cretaceous  sea.  At  the  beginning  of 
the  Tertiary  period,  the  Mississippi  probably  commenced  to  run  into 
the  Tertiary  embayment,  shown  in  Fig.  844  (p.  505).  The  Red  and 
Arkansas,  if  they  then  existed,  were  not  tributaries,  but  separate  rivers, 
emptying  into  the  same  embayment.  The  Ohio  was  almost,  if  not 
quite,  a  separate  river  also.  During  the  early  Glacial  epoch,  the  whole 
embayment  of  the  Gulf  was  abolished  by  elevation.  This  is  clearly 
demonstrated  by  the  torrential  pebble-deposit  (Orange  sand),  and  by 
the  stump-layer  (old  forest-ground),  found  by  Hilgard  beneath  the 
Port  Hudson  (Champlain)  deposit,  on  the  shores  of  the  Gulf.  During 
the  same  epoch,  by  reason  of  this  elevation,  the  great  trough,  represented 
in  Fig.  933,  was  scooped  out  of  the  Tertiary  strata,  200  to  500  feet 
deep,  by  the  erosive  power  of  water,  favored  by  the  greater  slope  of  the 
country  southward  at  that  time,  and  also  by  the  greater  water-supply. 
During  the  Champlain  epoch,  by  subsidence  this  great  trough  became 
an  arm  of  the  Gulf,  or  an  estuary,  fifty  to  one  hundred  miles  wide,  and 
reaching  up  to  the  mouth  of  the  Ohio,  with  extensions  up  the  tribu- 
taries ;  and  this  estuary  became  filled,  200  to  500  feet  deep,  with  sedi- 
ments. This  deposit  was  at  first  estuarian  (Port  Hudson),  and  after- 
ward river-silt  (Loess).  At  the  same  time  the  Mississippi  was  con- 
nected with  the  Great  Lakes,  then  greatly  enlarged,  and  with  Lake 
Winnipeg,  then  also  greatly  enlarged,  as  Lake  Agassiz.  During  the 
Terrace  epoch,  this  silt  was  laid  bare,  and  the  river  commenced  and 
continued  to  cut,  until  the  bluffs  became  200  to  400  feet  high.  Finally, 
during  the  Recent  epoch,  the  river  has  again  commenced  building  up 
by  sedimentation,  showing  thus  a  slight  depression  again,  or  at  least 
a  cessation,  of  the  re-elevation  of  the  Terrace  epoch.  This  up-building 


562  CENOZOIC   ERA— AGE   OF  MAMMALS. 

by  sedimentation  has  continued  up  to  the  present  moment,  and  the 
deposit  (river-swamp  and  delta  deposit)  has  reached,  according  to 
Hilgard,  a  thickness  of  fifty  to  a  hundred  feet.  Thus  the  phen- 
omena of  the  Mississippi  distinctly  separate  the  Terrace  from  the  Ke- 
cent  epoch. 

Quaternary  Period  on  the  Western  Side  of  the  Continent. 

All  the  most  characteristic  phenomena  of  this  period,  such  as  old 
sea-margins,  general  glaciation,  flooded  lakes,  and  old  river-beds,  are 
abundant  and  conspicuous  on  the  western  side  of  the  continent.  As 
it  is  impossible  to  synchronize  perfectly  these  phenomena  with  those 
already  described  on  the  eastern  side,  it  will  be  best  to  take  them  in  the 
order  named  above  and  trace  each  kind  through  the  whole  period. 

1.  Sea. — The  phenomena  along  the  sea-coast  show  both  elevation 
and  depression.  A  more  elevated  condition  than  the  present  is  shown 
by  the  bold,  rocky  coast  and  high  island  standing  a  little  way  off  the 
coast.  The  islands  off  the  coast  of  the  southern  part  of  California,  and 
separated  from  the  mainland  by  the  Santa  Barbara  Channel,  are  evi- 
dently continental  islands.  They  were  undoubtedly  a  part  of  the  con- 
tinent during  the  late  Tertiary  and  early  Quaternary  times,  and  were 
separated  subsequently  by  subsidence.  This  is  clearly  shown  by  their 
flora,*  and  especially  by  the  remains  of  the  Mammoth  on  one  of  them 
— Santa  Eosa.f  Another  very  striking  proof  of  continental  elevation, 
is  found  on  this,  as  on  the  Eastern  coast,  in  the  existence  of  deep  sub- 
marine channels  cutting  through  the  submerged  continental  plateau, 
and  evidently  produced  by  subaerial  erosion  during  late  Tertiary  times. 
I  am  indebted  to  Prof.  Davidson  for  facts,  yet  unpublished,  concerning 
these.  There  are  about  twenty  of  these  off  the  California  coast,  nine 
or  ten  of  which  are  very  marked.  Commencing  at  Cape  Mendocino, 
and  going  southward,  four  very  deep  ones  are  found  in  25  miles — one, 
very  marked,  in  the  Bay  of  Monterey,  one  in  Carmel  Bay,  one  off  the 
eastern  entrance  of  Santa  Barbara  Channel,  two  in  the  Bay  of  Santa 
Monica,  and  one  off  the  harbor  of  San  Diego.  These  channels  show  a 
previous  elevation  of  2,500  to  3,000  feet.  But  there  is  one  peculiarity 
of  these  as  compared  with  those  on  the  Eastern  coast,  viz.,  that  they 
do  not,  in  any  evident  way,  correspond  to  the  mouths  of  the  present 
rivers,  but,  on  the  contrary,  often  abut  against  a  bold  coast,  rising  to 
3,000  feet  within  three  miles  of  shore.  The  explanation  of  this  differ- 
ence is  found  in  the  enormous  orographic  changes  which  occurred 
on  this  coast  in  early  Quaternary  times.  Of  this  we  will  speak  again. 

*  American  Journal  of  Science,  vol.  xxxiv,  p.  457,  1887. 

f  Proceedings  of  the  California  Academy  of  Science,  vol.  v,  p.  152.  The  remains  of 
two  more  elephants  were  found  on  Santa  Rosa,  in  October,  1890,  by  Mr.  C.  D.  Voy. 


QUATERNARY  PERIOD  ON  THE  WESTERN  SIDE  OF  THE  CONTINENT.  563 

Subsequent  subsidence  and  partial  re-elevation  are  still  more  clear- 
ly shown  by  raised  sea-margins.  During  this  period  of  subsidence 
(Champlain),  the  Bay  of  San  Francisco  covered  all  the  flat  lands  about 
the  bay,  and  all  the  valley  continuations  of  the  bay,  north  and  south, 
such  as  Sonoma  and  Napa  Valleys  on  the  north  and  Santa  Clara  Val- 
ley on  the  south.  Also  the  sea  then  passed  through  the  Strait  of  Car- 
quinez  and  covered  the  whole  San  Joaquin  and  Sacramento  plains, 
forming  a  great  interior  sea  300  miles  long  and  50  miles  wide.  The 
margins  of  this  sea  are  still  visible  in  the  upper  Sacramento  Valley. 
At  the  same  time  the  sea  entered  the  Columbia  River  and  spread  over 
the  Willamette  Valley,  forming  a  great  sound,  and  passed  up  to,  and 
possibly  beyond,  the  Cascades.  About  Puget  Sound  similar  evidences 
of  former  extension  are  plain,  especially'at  the  southern  end  ;  while  in 
British  Columbia  Dawson  finds  old  sea-margins  up  to  2,000  or  even 
3,000  feet  above  the  present  sea-level.  During  the  Terrace  period,  the 
coast-line  was  re-elevated  to  its  present  level,  leaving  successive  lower 
terraces  which  are  conspicuous  in  some  places.  Lake  Tulare  is  a  rem- 
nant of  the  interior  San  Joaquin  Sea,  although  it  was  probably  first 
freshened  by  an  outlet  into  the  San  Joaquin  River,  and  again  salted  by 
loss  of  its  outlet. 

2.  Ice. — We  have  already  (p.  265)  spoken  of  a  great  elevation  of  the 
Sierra  Range,  which  occurred  at  the  beginning  of  the  Quaternary. 
This  mountain-lifting  doubtless  contributed  to  the  development  of  gla- 
cial phenomena  at  this  time,  but  must  not  be  confounded  with  the 
general  continental  elevation  which  took  place  at  the  same  time,  as 
shown  by  the  sea-margin  phenomena. 

During  the  fullness  of  glacial  times — as  shown  by  Dawson  * — a 
continental  ice-sheet  covered  nearly  the  whole  of  British  Columbia, 
Northwest  Territory,  and  Alaska,  connecting  in  high  latitudes  with  the 
Eastern  sheet.  The  center  of  radial  movement  was  a  high  area  ex- 
tending from  55°  to  59°  north  latitude.  From  this  area  the  ice  moved 
southward,  southwestward,  westward,  and  even  northwestward.  South- 
ward it  certainly  reached  beyond  48°.  Westward  it  flowed  over  the 
Coast  Ranges,  filled  the  valleys  (now  submerged),  separating  the  great 
coast  islands  from  the  mainland,  flowed  over  these  islands,  and  ran  into 
the  sea  beyond. 

At  the  same  time  it  is  certain  that  the  Sierra f  was  completely 
mantled  with  snow ;  and  great  glaciers,  some  of  them  40  to  50  miles 
long  filled  all  the  profound  canons  which  trench  its  flanks.  At  the 
same  time  also  there  is  some  evidence  that  even  the  Coast  Ranges, 

*  Geological  Magazine,  vol.  v,  p.  347,  1888. 

f  For  a  fuller  account  of  the  glaciers  of  the  Sierra,  and  the  condition  of  things  during 
the  Glacial  epoch,  see  American  Journal  of  Science,  vol.  iii,  p.  325,  and  vol.  x,  p.  26. 


564:  CENOZOIC  ERA— AGE   OF  MAMMALS. 

favored  by  proximity  to  the  sea,  had  their  perpetual  snow-cap  from 
which  issued  glaciers  filling  the  principal  valleys.* 

It  is  impossible  to  describe  all  the  great  ancient  glaciers  whose 
tracks  have  been  traced.  They  filled  all  the  larger  canons,  and  their 
tributaries  all  the  higher  and  smaller  valleys  and  meadows.  Their 
tracks  are  everywhere  marked  by  glaciation  and  strewed  bowlders,  and 
their  terminus  at  different  times  by  a  succession  of  terminal  moraines 
and  lakelets.  We  will  mention  three  or  four  as  examples  : 

a.  During  the  epoch  spoken  of,  a  great  glacier,  receiving  tributaries 
from  Mount  Hoffman,  Cathedral  Peaks,  Mount  Lyell,  and  Mount  Clark 
groups  filled  Yosemite  Valley,  and  passed  down  Merced  Canon.    The 
evidences  are  clear  everywhere,  but  especially  in  the   upper  valleys, 
where  the  ice-action  lingered  longest. 

b.  At  the  same  time  tributaries  from  Mount  Dana,  Mono  Pass,  and 
Mount  Lyell,  met  at  the  Tuolumne  meadows  to  form  an   immense 
glacier,  which,  overflowing  its  bounds  a  little  below  Soda  Springs,  sent 
a  branch  down  the  Tenaya  Canon  to  join  the  Yosemite  glacier,  while 
the  main  current  flowed  on  down  the  Tuolumne  Cafion  and  through 
Hetchhetchy  Valley.     Kriobs  of  granite,  500  to  800  feet  high,  standing 
in  its  pathway,  were  enveloped  and  swept  over,  and  are  now  left  round, 
and  polished,  and  scored,  in  the  most  perfect  manner.     This  glacier 
was  at  least  forty  miles  long  and  1,000  feet  thick  at  Soda  Spring  for  its 
stranded  lateral  moraine  may  be  traced  so  high  along  the  slopes  of  the 
bounding  mountain,  and  2,500  thick  farther  down,  for  it  filled  Hetch- 
hetchy Valley  to  the  brim. 

c.  The  Sierra  range  on  its  western  side  slopes  gradually  for  fifty  or 
sixty  miles ;  but  on  the  eastern  side  it  is  very  precipitous,  so  that  the 
plains  5,000  to  7,000  feet  below  the  crest  are  reached  in  four  or  five 
miles.    In  glacial  times  long  and  complicated  glaciers  with  many  tribu- 
taries occupied  the  western  slope,  while  on  the  eastern  slope  innumer- 
able short,  simple  glaciers  flowed  in  parallel  streams  down  the  steep  in- 
cline and  out  for  several  miles  on  the  level  plain,  or  even  into  the  waters 
of  Lake  Mono.     One  of  the  largest  of  these  took  its  rise  in  the  snow- 
fields  about  Mono  Pass,  flowed  down  Bloody  Cafion,  and  six  to  seven 
miles  out  on  the  plain,  and  evidently  into  the  waters  of  Lake  Mono, 
which  was  then  far  more  extensive  and  higher  than  now.    Parallel  mo- 
raines, 300  feet  high,  formed  by  the  dropping  of  glacial  debris  on  each 
side  of  the  icy  tongue,  as  it  ran  out  on  the  plain  or  on  the  bottom  of 
the  shallow  lake,  are  very  conspicuous,  as  are  also  the  successive  ter- 
minal moraines  left  in  the  subsequent  retreat.     Behind  these  moraines 
water  has  accumulated,  forming  lakelets. 

*  Undoubted  marks  of  ancient  glaciers  are  found  about  Berkeley,  300  feet  above  the 
bay. 


QUATERNARY  PERIOD  OX  THE  WESTERN  SIDE  OF  THE  CONTINENT.  565 

d.  Many  glaciers,  whose  tracks  are  still  easily  traced,  at  that  time 
ran  down  the  steep  mountain-slope  into  Lake  Tahoe.  The  most  con- 
spicuous of  these  are  three  at  the  southern  end,  which,  issuing  from  as 
many  cafions,  ran  out  on  the  level  plain  three  or  four  miles,  and  into  the 
swollen  waters  of  the  lake  to  form  icebergs.  The  beautiful  lakelets  and 
the  lake-like  bay  which  form  so  conspicuous  a  feature  of  the  scenery  of 
the  southern  end  of  the  great  lake,  were  partly  scooped  out  by  these 
steeply  descending  glaciers,  and  partly  dammed  by  the  debris  left  when 
they  retired ;  and  the  long,  parallel  ridges  of  earth  and  bowlders  bor- 
dering the  lakelets  and  stretching  down  to  the  shores  of  the  great  lake, 
are  lateral  moraines  dropped  on  each  side  as  the  glaciers  ran  out  into 
the  lake*  (Fig.  934). 

During  the  Terrace  epoch  all  these  glaciers  of  the  Sierra  retreated, 
leaving  very  distinct  terminal  moraines,  where  they  rested  awhile,  be- 


w 


L.    TAHOE 


FIQ.  934.— Diagram  of  Moraines  at  the  Southern  End  of  Lake  Tahoe  :  a,  Fallen-Leaf  Lake  ;  ft,  Cas- 
cade Lake  ;  c,  Emerald  Bay. 

hind  which,  drainage- waters  accumulating,  have  formed  beautiful  little 
lakes.  Thus  they  have  gone  backward  and  upward,  until  they  have 
now  mostly  retired  within  the  snow-fields  which  gave  them  birth. 

*  American  Journal  of  Science,  vol.  x,  p.  126,  1875. 


566 


CENOZOIC   ERA— AGE   OF  MAMMALS. 


The  feeble  remains  of  some  may  still  be  found  hidden  away  among  the 
coolest  and  shadiest  hollows  of  the  highest  summits. 

Lakes. — A  period  of  flooded  lakes,  marked  by  successive  terraces 
about  the  present  lakes,  is  well  shown,  especially  in  the  Basin  region. 
The  period  of  the  flooded  lakes  in  this  region  seems  to  have  corre- 
sponded with  the  Glacial  epoch,  for  the  great  glaciers  ran  into  some  of 
them. 

About  Lake  Mono  there  are  five  or  six  very  distinct  terraces,  the 
highest  being  about  700  feet  above  the  present  water-level.  Evidently 
at  that  time  the  water  washed  against  the  steep  slope  of  the  Sierra, 
and  many  of  the  glaciers  in  this  region  ran  into  it.  About  Salt  Lake, 
several  terraces  are  very  conspicuous,  the  highest  being  about  1,000  feet 
above  the  present  lake-level.  Traced  out  by  this  highest  level,  the  out- 
line of  the  lake  embraced  an  enormous  area.  Similarly  about  all  the 
saline  lakes  of  the  Nevada  basin  terraces  have  been  traced  up  to  more 
than  600  feet  above  the  present  level.  In  general  terms,  we  may  say 
that  the  Basin  region  at  that  time  was  occupied  by  two  great  lakes : 
the  one  filling  the  Utah  basin,  the  other  the  Nevada  basin,  the  eastern 
shore  of  the  one  washed  against  the  Wahsatch,  the  western  shore  of 


FIG.  9a5.— Map  of  the  Quaternary  Lakes  Bonneville  and  Lahontan  (after  Gilbert  and  Russell). 

the  other  against  the  Sierra.  The  former  has  been  accurately  mapped 
by  Gilbert  and  called  Lake .  Bonneville — the  latter,  also  accurately 
mapped  by  King  and  Kussell,  and  called  Lake  Lahontan,  in  honor  of 
these  early  explorers.  Lake  Bonneville  when  at  its  1,000-feet  level, 
emptied  northward  into  the  Snake  and  Columbia  Rivers.  It  eroded  its 
outlet  down  to  the  600-feet  level ;  there  lost  its  outlet  and  dried  away  to 
its  present  condition.  Lake  Lahontan  when  at  its  600-feet  level,  had 


QUATERNARY  PERIOD  ON  THE  WESTERN  SIDE  OF  THE  CONTINENT.  567 


a  complicated,  deeply-dissected  outline,  with  the  numerous  mountain- 
ridges  of  the  Basin  region  forming  high  islands  and  promontories.  So 
far  as  known,  it  had  no  outlet.  As  the  Quaternary  period  passed  away, 
these  great  lakes  dried  away  more  and  more.  The  residues  of  the  one 
are  Great  Salt  Lake,  Utah  Lake,  and  Sevier  Lake ;  of  the  other,  Pyra- 
mid, Winnemucca,  Humboldt,  Carson,  Walker,  and  Soda  Lakes.  If  in 
the  East,  the  Quaternary  lakes  mostly  drained  away,  in  the  West  they 
mostly  dried  away  to  their  present  condition.  The  map  (Fig.  935) 
gives  outlines  of  these  two  great  lakes  and  their  present  residues. 

In  both  of  these  great  lakes,  according  to  Gilbert  and  Russell,  there 
are  abundant  evidences  of  two  flooded  periods  separated  by  a  period 
of  complete  desiccation.  If  the  flooded  periods  correspond  with  peri- 
ods of  great  development  of  the  ice-sheet,  as  seems  probable,  we  have 
here  also — as  in  the  eastern  part  of  the  continent — two  Glacial  periods 
separated  by  an  interglacial. 

River-Beds. — Old  river-beds  are  found  in  many  countries,  and  es- 
pecially in  the  Drift  region  of  the  Eastern  portion  of  our  continent 
(p.  557),  but  those  of  California  are  peculiar.  In  the  East  and  else- 
where, the  Tertiary  river-beds  are  in  the  same  places,  but  below  the 
present  river-beds ;  in  California  they  are  far  above,  and  in  many  cases 


FIG.  936.— Map  of  a  portion  of  the  Region  of  the  Deep  Placers  of  the  Ynba  River:  The  black,  lava- 
flows;  the  dotted  spaces,  gravel  (after  Whitney). 

in  different  places — i.  e.,  the  rivers  have  been  displaced  from  their 
former  beds  and  cut  much  deeper.    In  map  (Fig.  936)  we  give  a  portion 


568 


CENOZOIC  ERA— AGE  OF  MAMMALS. 


of  the  country  about  the  upper  Yuba,  and  Fig.  937  is  an  ideal  section 
across  the  river-beds  along  the  line  N  S,  Fig.  936.    It  is  seen  that  there 


si 


FIG.  937. — Section  along  the  Line,  north  and  south:  r'  r',  old  river-beds;  r  r,  present  river-beds;  Z, 

lava;  si,  slate. 

are  remnants  of  old  lava-flows  on  the  divides  between  the  deep  river- 
channels.  Beneath  these  lavas  there  are  river-gravels,  and  beneath  these 
trough-shaped  river-beds,  with  their  smoothly  and  variously  eroded  bed- 
rock. The  section  shows,  moreover,  that  the  present  rivers  have  com- 
menced their  beds  on  the  old  divides  (shown  by  dotted  lines),  but  have 
cut  much  deeper,  leaving  the  old  beds  high  up  on  the  present  divides. 

Such  are  the  facts  The  history  of  the  process  is  briefly  as  follows  : 
At  the  end  of  the  Tertiary  there  was  an  outburst  of  lava  near  the  crest 
of  the  Sierras.*  The  lava  flowed  down  the  river-beds,  filled  them  up, 
and  displaced  the  rivers.  These  immediately  commenced  cutting  new 
beds  on  the  old  divides,  because  the  lava  was  thinner  or  absent  there. 
Now,  coincidently  with  the  lava-flow,  there  was  an  elevation  of  the 
Sierra  crest  %  tilting  of  the  Sierra  crust-Mock  (p.  265),  and  therefore 
increase  of  the  Sierra  slope.  Such  tilting  was  attended  with  enormous 
displacement  or  faulting  on  the  eastern  side,  as  already  explained 
On  account  of  the  increased  slope,  the  rivers  seeking  their  base- 
level  cut  down  far  below  their  previous  level.  This  increase  of  slope 
is  shown,  if  possible,  still  more  plainly,  in  some  of  the  rivers  of  the 
southern  part  of  the  State,  beyond  the  limits  of  the  lava-flow.  Here 
also  the  tilting  and  the  increased  slope  took  place,  but  the  rivers  were 


FIG.  938.— Ideal  Section  across  a  River-bed  in  Southern  California  beyond  the  Region  of  the  Lava- 
flow. 

not  displaced.     They,  therefore,  retained  their  beds,  but  deepened  their 
channels,  leaving  the  old  river-gravels  high  up  on  their  sides  (Fig.  938). 

*  The  great  lava-flooding  of  the  Tertiary  commenced  probably  at  the  end  of  the  Mio- 
cene, and  continued  through  the  Pliocene.  These  flows,  in  California,  seem  to  have  been 
the  last. 


THE   QUATERNARY   PERIOD   IN  EUROPE.  569 

This  elevation  of  the  Sierra  took  place  at  the  end  of  the  Tertiary  or 
beginning  of  the  Quaternary,  and  doubtless  contributed  greatly  to  the 
severity  of  the  glaciation  in  California,  but  must  not  be  confounded 
with  the  northern  continental  movement,  which  occurred  about  the 
same  time,  and  was  far  more  efficient  in  determining  general  glaciation. 
Coincident  with  the  Sierra  elevation  by  block-tilting,  as  already  ex- 
plained (p.  205),  similar  orogenic  movements  took  place  in  the  Basin 
region.  Thus  it  is  seen  that  the  river-beds  of  California  show,  not  con- 
tinental crust-oscillations  like  those  of  the  East,  but  mountain-making 
by  crust-block-tilting. 

We  have  seen  that  the  submarine  channels  of  the  California  coast 
differ  from  those  of  the  Eastern  coast,  in  that  they  are  not  continuous 
with  the  present  subaerial  river-channels.  We  have  also  just  seen  that 
the  river-beds  of  the  Sierra  differ  from  those  on  the  Eastern  coast,  in 
that  they  have  been  displaced  from  their  old  positions,  and  have  cut 
much  deeper.  Now,  the  reason  of  this  difference  is  probably  the  same 
in  the  two  cases,  viz.,  recent  orogenic  changes.  We  have  seen  that  the 
Sierra  took  its  present  form  and  height  at  the  beginning  of  the  Qua- 
ternary. It  is  probable  that  great  orogenic  changes  occurred  at  the 
same  time  in  the  Coast  Range  also.  In  both  cases,  too,  the  orogeny  was 
attended  with  floods  of  lava.  Much  of  the  lava,  and  presumably  many 
of  the  ridges  of  the  Coast  Range,  were  formed  at  that  time.  By  these 
changes  the  mouths  of  the  rivers  were  changed  from  their  original  places. 

History  of  the  Sierra  Range. — This  range  was  born  out  of  the  ocean 
by  horizontal  crushing  and  bulging,  as  already  explained  (p.  252),  at 
the  end  of  the  Jurassic.  During  the  whole  Cretaceous  and  Tertiary  it 
was  subjected  to  erosion,  until  by  the  end  of  that  time  the  rivers  had 
reached  their  base-levels,  and  the  range  was  reduced  to  very  moderate 
height.  The  crest  was  then  about  the  region, of  the  Yosemite,  for  the 
erosion  into  the  granite  is  deepest  about  that  region.  Then  came,  at 
the  end  of  the  Tertiary  and  beginning  of  the  Quaternary,  the  tilting  of 
the  Sierra  earth-block,  the  formation  of  the  great  fault-cliff,  and  the 
transference  of  the  crest  to  the  extreme  eastern  side ;  the  outpouring 
of  the  lava ;  the  displacement  of  the  rivers ;  and  the  cutting  of  the  new 
river-beds.  By  this  great  movement,  the  already  old  Sierra  was  re- 
juvenated, and  entered  upon  a  new  cycle  of  changes  by  erosion,  which 
is  still  progressing. 

The  Quaternary  Period  in  Europe. 

In  Europe  the  phenomena  were  more  irregular,  the  oscillations 
more  numerous,  and  perhaps  more  local,  than  in  America.  This  is  in 
accordance  with  the  general  difference  in  the  geological  history  of  the 
two  continents.  Nevertheless,  the  general  character  of  the  phenomena 
was  similar  in  the  two  countries. 


570 


CENOZOIC  ERA— AGE   OF  MAMMALS. 


1.  Epoch  of  Elevation — Glacial  Epoch. — During  the  Early  Qua- 
ternary the  whole  of  Northern  Europe  seems  to  have  been  elevated 
1,000  to  1,500  feet  and  sheeted  with  ice.  The  continental  margin  was 
considerably  farther  west  than  now,  especially  in  the  region  of  the 
British  Isles,  which  were  then  a  part  of  the  continent,  there  being  then 
no  Baltic  and  North  Sea.  The  area  of  highest  elevation  and  of  thickest 
ice,  and  therefore  of  radial  movement,  was  the  Scandinavian  Penin- 
sula. From  this  area  the  ice  moved  westward  into  the  Atlantic,  as  far 
at  least  as  the  line  of  100  fathoms ;  southwestward  over  the  British 
Isles,  southward  over  the  beds  of  the  Baltic  and  North  Seas  and  into 
Northern  Germany  as  far  as  the  frontiers  of  Bohemia;  and  south- 


FIG.  939.— Map  of  Outline  of  Coast  of  Western  Europe,  if  elevated  600  Feet  (after  Lyell). 

eastward  and  eastward  over  Russia  as  far  as  Moscow,  glaciating  the 
whole  surface  in  its  course.     The  southern  boundary  of  the  ice-sheet 


THE   QUATERNARY   PERIOD    IN   EUROPE. 


571 


has  been  traced.  It  passed  through  Cornwall,  across  Dover  Strait, 
through  Middle  Germany  and  Southern  Russia  to  the  Ural  Mountains, 
following  nearly  the  50th  parallel  of  latitude.  In  Fig.  939  we  give  the 
outline  of  Western  Europe  if  raised  only  600  feet.  The  elevation  was 
much  more. 

At  the  same  time,  the  whole  Alpine  region  of  Middle  Europe,  al- 
though beyond  the  limits  of  the  ice-sheet,  was  mantled  with  snow  to  a 
degree  much  greater  than  at  present,  and  developed  glaciers  on  a  pro- 
digious scale.  Some  of  these  have  been  traced  out  with  great  care  and 
skill.  Especially  has  this  been  done  for  the  great  Rhone  glacier  by 
Guyot,  and  more  recently  by  Favre.  At  that  time  a  great  glacier  came 
down  the  valley  of  the  Rhone,  emerged  on  the  plains,  and  filled  the 
whole  valley  of  Switzerland,  fifty  miles  wide,  between  the  Alps  and  the 
Jura,  forming  a  great  mer  de  glace  50  miles  wide,  150  miles  long,  and 
4,000  to  5,000  *  feet  deep.  A  figure  is  given  below  of  this  great  glacier. 
The  dotted  lines  show  the  direction  of  motion  as  determined  by 
bowlders  left  in  the  valley  or  stranded  high  up  on  the  slopes  of  the 
Jura. 


FIG.  940  —Map  showing  the  Ontline  and  Conine 
of  Plow  of  the  Great  RhOne  Glacier  (after 
Lyell). 


FIG.  941. — Map  showing  the  Lines  of  Debris  ex- 
tending from  the  Alps  into  the  Plains  of  the 
Po  (after  Lyell). 


Lakes  Geneva  and  Neufchdtel  were  filled  and  their  bottoms  scoured 
by  this  great  glacier. 

At  the  same  time,  also,  on  the  southern  slopes  of  the  Alps,  long 
glaciers  stretched  out  on  the  plains  of  Lombardy,  as  shown  by  the  pro- 
digious piles  of  debris  (moraines)  still  left.  Some  of  these  moraines 
are  1,500  feet  high.  Fig.  935  is  a  map  of  these  lines  of  debris. 

*  Archives  des  Sciences,  vol.  Iviii,  p.  159,  1877,  and  vol.  iii,  p.  228,  1880. 


572 


CENOZOIC  ERA— AGE   OF  MAMMALS. 


Evidences  of  glaciers  of  this  time  are  also  found  in  the  Vosges,  in 
the  Pyrenees,  and  other  high  mountains  of  Central  Europe. 

During  this  time  also  Europe  was  probably  connected  with  Africa 
by  one  or  more  highways,  through  the  Mediterranean  Sea. 

In  Europe,  as  in  America,  there  are  evidences  of  a  temporary  re- 
treat and  readvance  of  the  ice-sheet — i.  e.,  of  two  glacial  and  an  inter- 
glacial  period. 

2.  Epoch  of  Subsidence — Champlain. — Following  the  epoch  of  ele- 
vation was  an  epoch  of  subsidence,  during  which  the  same  regions  which 


FIG.  942.— Map  of  the  British  Isles  and  Norway,  if  subsided  1,200  to  2,000  Feet  (after  Lyell).    The 
lower  shaded  portion  was  not  touched  by  Drift. 

were  before  most  elevated  became  now  most  depressed.  It  is  believed 
that  in  Scotland  the  land  was  at  least  2,000  feet  below  the  present 
level  By  this  depression  a  great  part  of  Northern  Europe  was  sub- 
merged, and  Great  Britain  was  reduced  to  an  archipelago  of  small 


SOME   GENERAL  RESULTS  OF  GLACIAL  EROSIOX.  573 

islets.  Over  the  area  thus  submerged  icebergs  loosened  from  the 
Scandinavian  ice-field  drifted. 

At  the  same  time,  partly  by  subsidence,  and  therefore  slackened 
water-currents,  and  partly  by  moderated  climate  and  melting  of  glaciers, 
there  was  a  flooded  condition  of  rivers  and  lakes  in  Middle  Europe, 
France,  Germany,  and  Switzerland.  At  the  same  time,  also,  the  north- 
ern portion  of  Asia  and  the  lake-region  of  that  continent  were  sub- 
merged. The  Caspian  Sea,  Lake  Aral,  and  other  lakes  in  that  region, 
were  probably  then  united  into  one  great  inland  sea,  connected  either 
with  the  Black  Sea  or  the  then  greatly-extended  Arctic  Ocean,  or  with 
both.* 

Evidences  of  this  condition  of  things  are  found  in  old  sea-margins, 
lake-margins,  river-terraces,  and  flood-plain  deposits. 

3.  Epoch  of  Re-elevation— Terrace  Epoch.— The  period  of  subsid- 
ence was  followed,  as  in  America,  by  a  re-elevation,  shown  by  succes- 
sive beaches  and  terraces  on  sea-shores,  about  lakes,  and  along  rivers. 
In  some  places,  the  re-elevation  seems  to  have  gone  beyond  the  present 
level,  and  the  British  Isles  for  a  brief  time  were  again  united  to  the 
continent.  Then  the  land  went  down  again  to  its  present  condition. 

Southern  Hemisphere. 

Similar  phenomena  to  those  described  have  been  observed  also  in 
the  Southern -Hemisphere,  especially  in  New  Zealand;  but  whether 
these  were  contemporaneous,  or  alternating  with  those  of  the  North- 
ern Hemisphere,  is  uncertain. 

Some  General  Results  of  Glacial  Erosion. 

1.  Fiords. — We  have  seen  that  the  phenomena  of  rivers,  in  the 
region  affected  by  the  Drift,  show  elevation,  then  subsidence,  and  then 
re-elevation  to  a  less  height  than  the  first.  The  first  elevation  is  shown 
in  their  deep,  ancient  beds ;  the  subsidence,  in  the  filling  up  of  these 
with  deposit ;  the  re-elevation,  in  the  cutting  down  into  the  deposit,  and 
forming  terraces.  Now,  all  these  changes  are  also  shown  in  the  phe- 
nomena of  fiords  (Dana). 

It  will  be  remembered  (p.  38)  that  the  Norway  coast  is  wonderfully 
bold  and  deeply  dissected,  consisting  of  high,  rocky  headlands,  sepa- 
rated by  deep  inlets  running  50  to  100  miles  into  the  country ;  and  off 
shore  there  is  a  line  of  high,  rocky  isles,  evidently  the  remnants  of  an 
old  shore-line.  These  deep  inlets  are  called  in  Norway  Fiords ;  and 
the  name  is  now  used  for  all  such  deep  inlets  separating  high  head- 
lands. The  coast  of  Greenland  has  a  precisely  similar  structure.  It, 

*  Nature,  vol.  xiii,  p.  74 ;  Natural  History  Magazine,  vol.  xvii,  p.  176 ;  Archives  dcs 
Sciences,  vol.  liv,  p.  427. 


574: 


CENOZOIC  ERA— AGE   OF  MAMMALS. 


also,  consists  of  bold,  rocky  headlands,  separated  by  fiords  running  far 
into  the  country ;  and  off  shore  a  line  of  rocky  isles  2,000  feet  high. 
In  Greenland  these  fiords  are  now  occupied  by  glacial  extensions  of  the 
general  ice-mantle.  The  same  coast-structure  is  found  on  the  western 
side  of  the  continent  in  high  latitudes.  The  coast  of  British  America 
and  Alaska  is  also  bold  and  deeply  dissected  by  fiords  ;  and  in  Alaska 
these  fiords  are  now  occupied  by  great  glaciers  running  down  to  the 
sea  (Fig.  943). 

The  fiords  of  Norway  have  been  attributed  (p.  38)  partly  to  the 
erosive  agency  of  waves  and  tides,  but  it  is  certain  that  they  are  mainly 
due  to  a  partial  subsidence  of  a  bold  coast  deeply  trenched  with  gorges. 
In  a  word,  fiords  are  deeply-eroded  valleys,  which  have  become  half 
submerged  ;  and,  as  glaciers  are  the  most  powerful  of  erosive  agents  in 
these  regions,  they  are  usually  half-submerged  glacial  valleys.  These 
valleys  can  in  most  cases  be  traced  as  submarine  troughs,  far  out  to  sea. 
In  Greenland,  for  instance,  the  extension  of  these  troughs,  deep  below 
the  present  sea-level  and  far  out  beyond  the  reach  of  the  present  gla- 
ciers, shows  a  former  more  elevated  condition ;  and  terraces  and  recent 
deposits  up  to  500  feet  show  a  subsidence  below,  and  a  re-elevation  to, 
the  present  level. 


FIG.  943.— Ideal  Section  through  a  Fiord. 

All  shores  in  northern  regions  are  bold  and  rocky  and  deeply  dis- 
sected, and  have  rocky  islets  off  shore ;  in  other  words,  are  more  or  less 
affected  with  fiord-structure.  They  have  been  elevated,  eroded,  and 
subsided.  It  is  probable  that  during  the  epoch  of  greatest  elevation  a 
broad  continental  connection  existed  between  America  and  Asia,  in- 
cluding the  whole  area  between  the  Aleutian  Isles  and  Bering  Strait. 

2.  Glacial  Lakes. — Lakes  are  found  in  nearly  all  countries,  and  are 
doubtless  due  to  many  different  agencies,  but  the  small  lakes,  so  abun- 
dant in  the  region  covered  by  the  ice-sheet  and  by  ancient  glaciers,  are 
undoubtedly  due  to  glacial  agency.  It  is  only  necessary  to  look  at  a 
good  map  of  the  United  States  to  see  at  once  the  great  contrast  in  this 
regard  between  the  Northern  and  Southern  parts.  In  the  single  State 
of  Minnesota  there  are  several  thousand  lakes.  South  of  the  line  of  the 
ice-sheet  there  is  not  one. 


LIFE  OF  THE  QUATERNARY  PERIOD.  575 

Glacial  lakes  are  formed  in  several  ways :  (a)  They  may  be  rock- 
basins  scooped  out  by  glaciers  where  the  rocks  are  softer  or  else  where 
there  is  a  sudden  change  in  the  slope  of  the  bed  from  a  higher  to  a 
lesser  angle ;  or  (b)  they  may  be  formed  by  the  damming  of  drainage 
waters  behind  terminal  moraines  of  a  retreating  glacier ;  or  (c)  by  the 
disappearance  of  snow  from  old  cirques,  the  fountains  of  ancient 
glaciers.  These  three  kinds  are  very  abundant  in  all  the  highest 
mountains,  such  as  the  Sierra  or  the  Colorado;  the  last  among  the 
highest  summits,  the  first  high  up  the  valleys,  and  the  second  a  little 
way  down.  Again  (d)  along  northern  coasts  elongated  lakes  are 
often  formed  by  the  elevation  of  fiords.  Many  lakes  in  Norway 
and  Scotland  are  formed  in  this  way;  (e)  lastly,  the  thousands  of 
small  lakes  which  over-sprinkle  the  surface  left  by  the  ice-sheet,  es- 
pecially after  its  second  advance,  are  due  to  irregular  dumping  of  gla- 
cial debris. 

It  is  necessary  to  remember  that  lakes  are  ephemeral  features  of 
topography.  They  are  inevitably  in  time  either  drained  away  by  down- 
cutting  of  their  outlets,  or  else  filled  up  by  sediments  brought  down 
from  above.  This  process  is  especially  rapid  in  mountain-regions. 
The  little  glacial  lakes  are  rapidly  being  filled  and  converted  into 
marshes  and  meadows.  Everywhere  in  the  Sierra,  the  region  of  mead- 
ows is  the  region  of  the  old  glaciers.  Lakes,  then — especially  small 
lakes — are  a  feature  of  new  topography.  The  topography  of  all  the 
Southern  States  is  extremely  old,  while  that  of  the  Northern  States  has 
been  largely  determined  by  the  Drift,  and  is  therefore  very  new. 

Life  of  the  Quaternary  Period. 

Plants  and  Invertebrates. — Remains  of  the  life  of  the  Quaternary/ 
both  animal  and  vegetable,  are  very  numerous,  and  often  very  well  pre- 
served. Both  the  plants  and  the  invertebrate  animals  are  almost  wholly 
identical  with  those  now  living  on  the  earth.  We  will  therefore  dis- 
miss these  with  one  important  remark :  The  plants  and  the  marine 
shells  show  an  arctic  climate  in  now  temperate  regions.  The  species 
found  are  still  living,  but  living  farther  north.  There  has  been  a  mi- 
gration of  species  northward  since  Glacial  times.  In  Tertiary  times 
(p.  507),  we  noted  a  migration  of  forms  southward,  indicating  a  con- 
trary change  of  climate  at  that  time. 

Mammals. — But  the  mammalian  fauna  of  the  Quaternary  is  almost 
wholly  peculiar.  It  differs  greatly  from  the  Tertiary  fauna  preceding, 
and  the  present  fauna  succeeding.  The  species  are,  moreover,  very 
numerous,  and  many  of  them  of  extraordinary  size ;  for  it  is  the  culmi- 
nation of  the  mammalian  age.  It  is  necessary,  therefore,  to  describe 
some  of  them,  and  the  conditions  under  which  they  were  preserved^ 
and  thus  to  realize  in  some  degree  the  conditions  under  which  they 


576 


CENOZOIC   ERA— AGE   OF   MAMMALS. 


lived.  We  will  take  our  first  illustrations  from  Europe,  because  the 
remains  are  more  numerous  and  have  been  more  thoroughly  studied 
there. 

Mammalian  remains  of  this  time  are  found  in  Europe — 1.  In  caverns, 
where  in  great  numbers  they  have  become  entombed ;  2.  On  beaches 


and  terraces,  where  their  floating  carcasses  have  become  stranded ;  3. 
In  marshes  and  peat-bogs,  where,  venturing  in  search  of  food,  they  have 


LIFE  OF  THE  QUATERNARY  PERIOD.  577 

mired  and  perished ;  4.  In  ice-cliffs  and  frozen  soils,  where  they  have 
been  hermetically  sealed  and  preserved  to  the  present  time. 

1.  Bone-Caverns. — The  richest  sources  of  Quaternary  mammalian 
remains  are  undoubtedly  bone-caverns.  These  occur  in  nearly  all  coun- 
tries, often  along  the  course  of  streams,  but  high  above  the  present 
stream-level.  Their  formation  and  their  filling  are  in  some  way  con- 
nected with  the  floods  of  the  Interglacial  and  Champlain  epochs. 
They  are  rich  in  organic  remains  to  a  degree  which  is  almost  incredi- 
ble. One  of  the  most  striking  peculiarities  of  these  remains  is,  that 
they  often  consist  of  a  heterogeneous  mixture  of  all  kinds,  carnivorous 
and  herbivorous,  and  all  sizes,  from  the  Elephant  and  Cave-bear  on  the 
one  hand  down  to  Rats  and  Weasels  on  the  other ;  sometimes  perfect, 
more  often  broken,  mingled  with  earth  and  gravel,  forming  unstratified 
bone-rubbish.  Another  peculiarity  of  these  deposits  is  that  they  are 
often  covered  and,  as  it  were,  sealed  by  a  stalagmitic  crust  formed  by 
subsequent  drippings  from  the  roof,  and  thus  preserved  against  even 
the  suspicion  of  disturbance  to  the  present  time.  We  give  (Fig.  944) 
a  section  of  the  cave  of  Gailenreuth,  with  its  bone-rubbish  and  stalag- 
mitic crust. 

Among  the  remains  of  Herbivores  found  in  bone-caverns,  the  most 
remarkable  are  those  of  the  Elephant,  Rhinoceros,  Hippopotamus,  the 
great  Irish  Elk,  besides  Horses  and  Oxen.  Among  Carnivores  are  the 
Cave-bear  ( Ursus  spelaus),  larger  than  the  Grizzly,  the  Cave-hyena,* 
the  Cave-lion,*  the  Saber-toothed  Tiger  (Machairodus  latidens),  with  its 
saber-like  tusks,  ten  inches  long,  besides  smaller  animals  of  the  same 
order.  The  remains  of  the  larger  Carnivora,  especially  the  Cave-bear 


Fio.  945.— Skull  of  Ureas  spelseus,  x  J. 

and  the  Cave-hyena,  are  the  most  abundant.    The  bones  of  the  smaller 
Herbivores  bear  the  marks  of  teeth,  as  if  they  had  been  gnawed.    The 

*  These  are  supposed  to  be  the  same  species  as  the  African  lion  and  hyena  of  the 
present  day,  but  much  larger. 
37 


578  CENOZOIC  ERA— AGE   OF  MAMMALS. 

skeletons  of  the  large  Pachyderms  are  usually  more  perfect.  In  the 
Kirkdale  Cave,  England,  the  teeth  and  other  parts  of  300  individuals  of 
the  Cave-hyena  were  found.  In  the  Gailenreuth  Cave,  Franconia,  the 
remains  of  800  Cave-bears  were  obtained.  In  a  Polish  cave  Homer 
recently  found  the  remains  of  at  least  1,000  Cave-bears,*  and  from  one 
in  Sicily,  twenty  tons  of  hippopotamus-bones  have  been  taken. f  In 


FIG.  946.— Skull  of  Hyena  spelaea,  x  J. 

many  bone-caves  are  found  also  the  bones  and  rude  implements  of 
primeval  man.  Of  these  we  will  speak  more  fully  hereafter. 

Origin  of  Cave  Bone-Rubbish. — When  it  was  supposed  that  the  Drift 
was  caused  by  a  great  wave  of  translation  sweeping  across  the  conti- 
nent and  carrying  ruin  in  its  course,  the  phenomena  of  bone-caves  were 
supposed  to  give  countenance  to  this  view.  Animals  of  all  sizes  and 
kinds  were  supposed  to  have  huddled  together  in  these  caves,  forget- 
ting their  mutual  hostility  in  the  sense  of  a  common  danger,  and  per- 
ished miserably  together  there. 

But  at  present  it  is  usually  believed :  1.  That  these  caves  were  the 
dens  of  the  larger  Carnivores,  especially  the  Cave-bear  and  Cave-hyena, 
which  dragged  their  prey  there  to  devour  them,  and  also  later  the 
abodes  of  men ;  2.  That  also  the  floating  bodies  of  large  Herbivores, 
such  as  the  Elephant,  Ehinoceros,  etc.,  were  carried  into  them  by  the 
flooded  rivers  which  then  ran  at  that  level ;  and  3.  That  during  the 
Champlain  epoch,  when  water  ran  through  these  caves  in  large  quanti- 
ties, bones  and  earth  were  drifted  in  from  above,  through  fissures  and 
subterranean  passages,  and  thus  found  their  lodgment  in  the  caves. 
This  last  was  probably  the  principal  source  of  the  bone-rubbish  in 
most  cases. 

Origin  of  Bone-Caverns. — In  limestone  regions  caverns  are  very 
abundant  everywhere.  They  do  not  seem  to  be  enlarging  now ;  but 
on  the  contrary  to  be  in  most  cases  filling  up  either  with  rubbish  or 
with  stalactitic  and  stalagmitic  deposit.  In  some  cases  streams  still  run 

*  Science,  vol.  iii,  p.  490,  1884.  t  Prestwich,  Geology,  vol.  ii,  p.  508. 


LIFE   OF   THE   QUATERNARY   PERIOD. 


579 


through  them.  It  seems  probable  that  they  are  mostly  due  to  the  ac- 
tion of  subterranean  waters  in  Champlain  times.  At  that  time  full 
streams  ran  through  and  excavated  them,  partly  by  erosion,  partly  by 
solution.  Gradually,  as  the  Terrace  elevation  came  on,  the  great 
streams  into  which  these  cavern  tributaries  ran  cut  down  their  beds  to 
lower  levels,  the  subterranean  waters  sought  lower  levels,  and  the  part 
running  through  the  caverns  was  reduced  to  drippings ;  and  stalagmitic 
crusts  covered  the  Champlain  rubbish  and  preserved  them.  Thus, 
then,  the  date  of  the  caves  is  Champlain ;  of  the  bone-rubbish  is 
Champlain  and  early  Terrace ;  of  the  stalagmitic  crust  is  later  Terrace 
and  Recent. 

2.  Beaches  and  Terraces. — On  these  are  found  the  remains  of  bodies 
which  have  floated  and  become  stranded.  The  most  abundant  of  these 
are  remains  of  Elephas  primiyenius  or  Mammoth.  It  is  believed  that 


PIG.  947.— Skeleton  of  the  Irish  Elk  (Cervus  megaceros),  Post-Pliocene,  Britain. 

the  bones  of  500  individuals  have  been  found  on  the  coast  of  Norfolk 
and  Suffolk,  and  over  2,000  grinders  have  been  dredged  up  by  the  fish- 


580 


CENOZOIC  ERA— AGE   OF  MAMMALS. 


ermen  of  the  little  village  of  Happesburgh  (Woodward).  On  river-ter- 
races associated  with  bones  of  Quaternary  animals  have  been  found  also 
the  rude  implements  of  primeval  man.  We  speak  of  these  more  par- 
ticularly hereafter. 

3.  Marshes  and  Bogs. — As  might  have  been  anticipated,  the  re- 
mains found  in  these  are  mainly  those  of  the  larger  Herbivores — ele- 
phants, oxen,  stags,  etc.      It  is  in  these  that  were  found  most  of 
the  fine  skeletons    of    the    gigantic   Irish  elk   (Cervus    megaceros). 
This  magnificent  elk  was  ten  to  eleven  feet  in  height  to  the  top  of 
its  palmate  antlers,  and  ten  to  twelve  feet  between  the  antler-tips  (Fig. 
947). 

4.  Frozen  Soils  and  Ice-Cliffs. — As  in  these  have  been  found  the  most 
perfect  specimens  of  the  Mammoth  (Elephas  primigenius),  this  seems 
to  be  the  proper  place  to  describe  the  animal. 


FIG.  948.— Skeleton  of  the  Mammoth  (Elephas  primigenhis).  Portions  of  the  integument  still  adhere 
to  the  head,  and  the  thick  skin  of  the  soles  is  still  attached  to  the  feet. 

The  genus  Eleplias  ranges  in  time  from  about  the  latter  part  of  the 
Miocene  to  the  present.  There  are  about  fifteen  fossil  species  known. 
The  genus  seems  to  have  reached  its  maximum  development  in  the 
Quaternary.  During  that  period  three  species  inhabited  Europe,  viz. : 
E.  antiquus,  E.  meridionalis,  E.  primigenius  (Lyell),  besides  two 
dwarf  species,  E.  Melitensis,  four  and  a  half  feet  high,  and  E.  Fal- 
coneri,  three  feet  high,  found  in  the  Quaternary  of  Malta.  Of  these, 


MAMMALIAN   FAUNA  IN  NORTH   AMERICA.  581 

the  largest,  the  most  numerous,  and  the  latest,  was  the  primigenius  or 
Mammoth.  This  species  roamed  in  immense  herds  all  over  Europe, 
from  the  shores  of  the  Mediterranean  to  Siberia,  and  extended  also  over 
the  northern  portions  of  North  America.  In  Siberia  the  tusks  are  so 
abundant  and  so  well  preserved  that  much  of  the  ivory  of  commerce  is 
got  from  this  source. 

The  Mammoth  (Fig.  948)  was  over  twice  the  bulk  and  weight  of 
the  largest  modern  species,  and  nearly  one  third  taller.  It  was  thick- 
ly covered  with  a  brownish  wool,  and  in  parts  with  long  hair ;  and 
was  therefore  well  adapted  to  endure  cold.  It  may  seem  strange  that 
we  should  speak  of  the  hair  and  wool  and  the  color  of  an  extinct 
animal ;  but  perfectly-preserved  specimens  have  been  found  sealed  in 
the  ice  in  Siberia — so  perfectly  preserved  that,  when  first  exposed, 
wolves  and  dogs  of  the  present  epoch  fed  on  the  flesh  of  this  animal 
belonging  to  an  extinct  fauna.  The  whole  skeleton,  with  portions 
of  the  skin,  hair,  wool,  hoofs,  and  eyes  of  this  animal,  is  now  to  be 
found  in  the  museum  at  St.  Petersburg.  The  existence  of  elephants 
so  far  north  does  not  indicate  a  warm  climate,  although  the  Cham- 
plain  epoch  was  doubtless  far  less  rigorous  than  the  Glacial.  These 
elephants  were  covered  with  thick  wool,  as  was  also  the  rhinoceros  of 
Europe. 

Quaternary  Mammalian  Fauna  of  England.— In  England  alone  there 
were,  in  Quaternary  times,  of  Carnivora,  the  great  Cave-bear,  the  Cave- 
hyena,  a  tiger  larger  than  the  Bengal,  the  sabre-toothed  tiger,  as  large, 
with  its  flat,  curved  tusks,  eight  inches  beyond  the  gums,  besides  wolves 
and  lesser  Carnivores.  Of  Herbivores,  there  were  the  Mammoth  in 
herds,  two  species  of  rhinoceros,  one  hippopotamus,  the  great  Irish  elk, 
three  species  of  oxen,  two  of  them  of  gigantic  size,  besides  horses,  deer, 
and  other  smaller  species.  Surely  this  was  the  culmination  of  the 
Mammalian  age  in  England. 

Mammalian  Fauna  in  North  America. 

The  animals  of  North  America,  in  Quaternary  times,  were  equally 
abundant ;  but  the  country  has  been  less  perfectly  explored,  and  the 
collections,  therefore,  less  complete.  Bone-caverns,  the  richest  sources 
of  European  collections,  are  also  far  more  rare. 

Among  Herbivores,  the  most  remarkable  were  the  great  Mastodon 
(M.  Americanus) ;  two  species  of  elephants,  the  E.  Americanus  and  the 
E.  primigenius  ;  at  least  two  gigantic  bisons,  one  of  which  was  prob- 
ably ten  feet  bet  ween  the  horn-tips;*  gigantic  horses ;  gigantic  beavers, 

*  A  specimen  of  Bos  latifrom  has  recently  been  found  in  Ohio,  the  horn-cores  of  which 
were  twenty  inches  around  the  base,  and  more  than  seven  feet  between  the  points.  Be- 
tween the  horn-tips  must  have  been  at  least  ten  feet. 


582  CENOZOIC   ERA— AGE   OF  MAMMALS. 

one  as  big  as  a  bear;  a  gigantic  stag  (Cervus  Americanus),  fully  as  large 
as  the  Irish  elk ;  tapirs,  peccaries,  and  a  large  number  of  Edentates,  an 
order  now  mostly  confined  to  South  America,  to  which  belong  the  sloths 
and  armadillos.  Many  of  these  were  also  of  gigantic  size.  Carnivores 
were  not  so  abundant  as  in  Europe.  The  most  remarkable  were  a  lion 
(Felis  atrox),  as  large  as  the  European,  and  two  species  of  bear  ( Ursus 
pristinus  and  amplidens). 

Bone-Caves. — Caves  are  found  in  limestone  regions  in  America  as 
elsewhere,  but  they  do  not  seem  to  have  been  to  the  same  extent  the 
dens  of  Carnivores.  In  a  vertical  opening  in  limestone  strata  in  Penn- 
sylvania, a  kind  of  cave,  mammalian  remains  have  been  found  belong- 
ing to  thirty-four  species,  among  which  were  six  Edentates,  eight  Un- 
gulates, and  twelve  Eodents.  A  number  have  also  been  found  in  the 
caves  of  Virginia,  and  a  few  in  those  of  Illinois  (Cope). 

Marshes  and  Bogs. — Most  of  the  remains  of  large  Herbivores  have 
been  found  in  marshes  and  bogs.  In  the  Big  Bone  Lick,  Kentucky, 
the  remains  of  one  hundred  mastodons  and  twenty  elephants  are  said 
to  have  been  dug  up.  Many  very  perfect  skeletons  of  the  great  masto- 
don have  been  obtained  from  marshes  in  New  York,  New  Jersey,  In- 
diana, and  Missouri.  One  magnificent  specimen  was  found  in  a  marsh 
near  Newburg,  New  York,  with  its  legs  bent  under  the  body  and  the  head 


Fiu.  949.— Mastodon  Americanus  (.after  Owen). 

thrown  up,  evidently  in  the  very  position  in  which  it  mired.  The  teeth 
were  still  filled  with  the  half-chewed  remnants  of  its  food,  which  con- 
sisted of  twigs  of  spruce,  fir,  and  other  trees  ;  and  within  -the  ribs,  in 


MAMMALIAN  FAUNA  IN  NORTH  AMERICA. 


583 


the  place  where  the  stomach  had  been,  a  large  quantity  of  similar  mate- 
rial was  found.  In  1866  a  very  perfect  skeleton  was  found  in  a  bog  at 
Cohoes,  New  York.  Many  others  have  been  found. 

The  Mastodon  Amencanus  (Fig,  949)  is  probably  the  largest  land- 
mammal  known,  unless  we  except  the  Dinotherium  (Gaudry).  It  was 
twelve  to  thirteen  feet  high,  and,  including  the  tusks,  twenty-four  to 
twenty-five  feet  long.  It  differed 
from  the  elephant  chiefly  in  the  char- 
acter of  its  teeth.  The  difference  is 
seen  in  Figs.  950,  951,  952.  The  ele- 
phant's tooth,  given  below  (Fig.  951), 


Fio.  950.— Tooth  of  Mastodon  Americanos. 


Fio.  951.— Perfect  Tooth  of  an  Elephas, 
found  in  Stanislaus  County,  Califor- 
nia, i  natural  size. 


is  sixteen  inches  long,  and  the  grinding  surface  eight  inches  by  four 
inches. 

The  two  genera  of  Proboscidians,  Elephas  and  Mastodon,  appeared 
together,  or,  more  probably,  the  mastodon  a  little  the  earlier,  in  the 
Miocene  epoch,  they  ranged  together  through  the  rest  of  the  Tertiary, 
the  species,  of  course, 
changing  several 
times.  At  the  end 
of  the  Tertiary,  the 
mastodon  became  ex- 
tinct on  the  Eastern 
Continent,  but  con- 
tinued through  the 
Quaternary,  with  its 

companion,    the    ele- 

,  •        A        • 

phant,    in    America. 

At  the  end  of  the 
Quaternary,  the  mas- 
todon became  extinct 
wholly,  and  the  ele- 

,  .  ,        Fio.  952.— Molar  Tooth  of  Mammoth  (Elephaa  primigenlus):  a, 

phant  in  America  and  grinding  surface;  ft,  side  view. 

Europe,  though  it  still 

continues  in  Asia  and  Africa.     During  the  Quaternary,  therefore,  one 

species  of  mastodon  and  two  species  of  elephant  roamed  in  herds  over 


584:  CENOZOIC  ERA— AGE   OF  MAMMALS. 

North  America  from  the  Gulf  to  arctic  regions.  Of  the  two  species  of 
elephant,  however,  the  primigenius  was  mostly  confined  to  the  higher 
latitudes,  and  the  Americanus  to  the  southern  portions.  The  latter  is 
distinguished  from  the  former  by  less  crowded  enamel  plates  in  the 
grinders  and  less  curved  tusks.  According  to  Cope,  about  fifty  species 
of  Proboscidians  are  known.  Of  these  five  are  Dinotheres,  twenty-five 
Mastodons,  six  Elephants,  and  five  of  uncertain  place.  The  Dino- 
therium  appeared  first,  then  the  Mastodon,  and  last  the  Elephant. 
This  is  also  the  order  of  specialization  of  teeth-structure.  The  order 
of  appearance  and  of  extinction  of  these  three  forms  are  shown  in  di- 
agram (Fig.  953). 

T  E:  F?  - 


EOCENE  M  IOC  EN  E  F»  L.  I O  C  E  N  E  QUATERNARY*        PRESENT 

FIG.  953.— Diagram  showing  Distribution  in  Time  of  Proboscidians. 

Among  Edentates,  a  Megatherium,  a  Megalonyx,  and  several  Mylo- 
dons,  have  been  found  in  North  America  ;  but,  as  their  principal  home 
was  in  South  America,  we  will  describe  them  under  that  head. 

River-Gravels. — In  many  portions  of  the  United  States,  but  espe- 
cially in  California,  remains  of  mastodon  and  elephant,  and  bison,  etc., 
are  found  in  great  numbers  in  river-gravels.  The  river-gravels  of  Cali- 
fornia are  spoken  of  again  further  on. 

Quaternary  in  South  America. — A  large  number  (more  than  100)  of 
species  of  mammals  have  been  found  in  the  soil  of  the  pampas  and  in  the 
caves  of  Brazil.  They  are  mastodons  (different  species  from  the  North 
American),  llamas,  horses,  tapirs,  rodents,  many  species  of  panther-like 
carnivores,  large  saber-toothed  tigers  (Machairodus  neogceus  and  neca- 
tor),  with  curved,  saber-like  tusks  twelve  inches  long  and  eight  inches 
beyond  the  gums  (Fig.  954),  and  especially  a  large  number  of  Edentates 
allied  to  the  sloths  and  armadillos,  but  of  gigantic  size. 

Of  the  Edentates,  the  most  remarkable,  in  fact,  one  of  the  most 
remarkable  animals  which  have  ever  existed,  is  the  Megatherium  (great 
beast)  Cuvieri.  The  genus  Megatherium  ranged  in  Quaternary  times 
through  South  America,  and  into  North  America,  as  far  as  the  shores 
of  Georgia  and  South  Carolina.  At  the  mouth  of  the  Savannah  Eiver 
the  remains  of  several  individuals  of  a  species  of  this  genus  (M.  mira- 
lilis}  have  been  found.  But  the  largest  species  and  the  most  perfect 
specimens  have  been  found  in  South  America. 

The  Magatlierium  Cuvieri,  of  which  we  give  a  figure  (Fig.  955),  was 
larger  than  a  rhinoceros,  but  was  still  more  remarkable  for  the  clumsy 
massiveness  of  its  skeleton  than  for  its  size.  This  is  especially  true  of 
its  hind-legs,  hip-bones,  and  tail.  For  this  reason,  it  is  supposed  to 


MAMMALIAN  FAUNA  IN   NORTH  AMERICA. 


585 


586 


CENOZOIC   ERA— AGE   OF  MAMMALS. 


have  been  able  to  stand  on  its  hind-legs  and  tail,  while  it  used  its  long 
free-moving  arms,  terminated   with  hands  a  yard  long,  to  tear  down 


FIG.  955.— Megatherium  Cnvieri. 

branches  on  which  it  fed.  The  great  skeleton  represented  above  is 
eighteen  feet  long,  and  its  thigh-bones  are  three  times  as  thick  as  those 
of  an  elephant.  The  grinding  surface  of  its  molar  teeth  (it  had  no 


FIG.  956.— Lower  Jaw  of  a  Megatherium,  showing  the  Gradual  Surface  of  the  Teeth  (after  Owen). 


FIG.  957.— Claw-Core  of  a  Megalonyx,  x  $  (drawn  from  a  cast  of  the  original). 


MAMMALIAN  FAUNA   IN   NORTH  AMERICA. 


587 


others)  is  traversed  by  triangular  ridges  admirably  adapted  to  triturate 
its  coarse  food. 

Megalonyx  (big  claw)  (Fig.  957)  is  the  name  of  another  genus  of 
these  gigantic  sloths,  and  Mylodon  of  a  third.  Both  of  these  genera 
extended  into  North  America.  In  fact,  the  Megalonyx  was  first  dis- 
covered in  Greenbrier  County,  Virginia,  and  named  Megalonyx  by 
Thomas  Jefferson.  The  larger  species  of  Mylodon  and  Megalonyx  were 
about  the  size  of  a  buffalo,  or  larger. 


Fio.  958.— Skeleton  of  Mylodon  robustus,  Quaternary,  South  America. 


Of  the  Armadillos  or  mailed  Edentates,  there  were  several  of  gi- 
gantic size  belonging  to  the  genera  Glyptodon,  Chlamydotherium,  and 
Pachytherium.  The  accompanying  cut  represents  one  of  these  eight 


Pio.  959.-— Skeleton  of  Glyptodon  clavipes,  x  J&,  Quaternary,  South  America. 


feet  long,  with  an  invulnerable  coat  of  mail.  Some  species  of  the  genus 
Chlamydotlierium  were  much  larger — one  as  big  as  a  rhinoceros,  and 
of  Pachytherium  as  big  as  an  ox  (Dana). 

^"<<    !£*••••      '»» 

$j>  o?  ran 

TTflrTVTZBSTTVl 


588 


CENOZOIC   ERA— AGE   OF  MAMMALS. 


Australia. — In  Australian  caves,  also,  great  abundance  of  remains 
has  been  found,  and  they  show  the  same  prevalence  of  gigantic  spe- 
cies. As  now,  so  then,  the  mammals  of  Australia  were  almost  all  Mar- 
supials^ but  the  present  species  are 
dwarfs  in  comparison.  The  largest  of 
these  was  the  Diprotodon  (two  front 
teeth),  a  pachydermoid  kangaroo  as  big 
as  a  rhinoceros.  A  reduced  figure  of 
the  skull,  which  was  three  feet  long,  is 
given  herewith. 

Among  other  remarkable  species  of 
marsupials  were  Macropus  (kangaroo) 
Titan  and  M.  Atlas,  of  great  size ;  Nototherium  MitcUelU,  as  large  as 
a  bullock,  and  a  very  remarkable  species,  supposed  by  Owen  to  have 
been  carnivorous,  and  therefore  called  Thylacoleo  (pouched  lion)  carn- 


FIG.    960.— Skull  of  Diprotodon  Aus- 
tralis,  x  £s,  Post-Pliocene,  Australia. 


FIG.  961.— Thylacoleo,  Skull  reduced  (after  Flower). 

if  ex,  as  large  as  a  lion.     The  striking  peculiarity  of  this  animal  was 
the  existence  of  a  broad  trenchant  premolar,  as  shown  in  Fig.  961. 

Geographical  Faunas  of  Quaternary  Times. — We  observe,  then,  that 
already  the  geographical  distribution  of  families  was  similar  to  that 
which  we  find  at  present.  Then,  as  now,  Herbivores  greatly  predomi- 
nated in  America,  while  Carnivores  were  very  abundant,  and  of  great 
size,  in  the  Eastern  Continent.  Then,  as  now,  sloths  and  armadillos 
and  llamas  characterized  the  fauna  of  South  America,  while  Marsupials 
characterized  that  of  Australia.  But  in  each  locality  the  animal  life 
seems  to  have  been  then  more  abundant,  and  the  species  gigantic. 


SOME   GENERAL   OBSERVATIONS  ON   THE   WHOLE   QUATERNARY.  593 

2.  Time  involved  in  the  Quaternary  Period.— If  we  accept  Croll's 
and  Wallace's  view,  then  it  is  possible  to  estimate  with  accuracy  the 
length  of  the  Glacial  epoch  and  the  time  elapsed  since  its  close,  for  it 
is  needless  to  say  that  astronomical  cycles  are  calculable  with  great 
certainty.  The  following  diagram,  taken  from  Mr.  Wallace,  shows  the 


THOUSAND  YEARS  AGO  FROM 

FIG.  904.— Diagram  of  Eccentricity  and  Precession:  Absciss  represents  time,  and  ordinates.  decrees 
of  eccentricity  and  also  of  cold.  The  dark  and  light  shades  show  the  warmer  and  colder  win- 
ters, and  therefore  indicate  each  10,500  years,  the  whole  representing  a  period  of  800,000  years. 

degrees  of  eccentricity  during  the  last  300,000  years,  and  the  recurring 
cycles  of  precession  during  that  period.  If,  as  he  thinks,  the  cold  was 
mainly  due  to  eccentricity  and  geographical  changes,  the  processional 
changes  having  little  effect,  then  this  figure  will  also  represent  the 
degrees  of  cold.  It  is  seen  that,  according  to  Croll  and  Wallace,  the 
Glacial  period  commenced  240,000  years  ago,  lasted  160,000  years,  and 
80,000  years  have  elapsed  since  its  decline.  It  is  seen  also  that  Mr. 
Wallace  makes  but  one  interglacial  period  instead  of  eight,  the  effect 
of  the  shorter  processional  cycles  being  tided  over  by  the  effect  of  the 
accumulated  ice. 

On  any  view  as  to  the  cause  of  the  glacial  climate,  there  can  be  no 
doubt  that  the  changes  which  produced  it  were  effected  very  slowly, 
and  therefore  involved  long  periods  of  time,  so  slowly  that  they  would 
probably  be  unobserved  by  contemporaneous  man,  if  such  existed. 
There  are  changes  by  elevation  and  depression  now  going  on  in  various 
parts  of  the  earth  which  are  probably  as  rapid  as  those  of  the  Glacial 
and  Champlain  epochs.  The  shores  of  the  Baltic  and  of  Norway  are 
now  rising  at  an  average  rate  of  two  and  a  half  feet  per  century.  Con- 
tinue this  rate  for  800  centuries,  and  Norway  would  attain  an  elevation 
as  great  as  that  of  the  Glacial  epoch,  and,  if  such  elevation  produces 
cold,  would  be  again  ice-sheeted.  Depression  at  a  similar  rate  for  the 
same  time  would  bring  about  a  condition  similar  to  that  of  the  Champ- 
lain  epoch.  Yet  these  changes  are  unremarked,  except  by  the  eye  of 
Science.  The  only  difference,  if  any,  between  what  is  in  progress  now 

38 


594  CENOZOIC  ERA— AGE   OF   MAMMALS. 

and  what  took  place  in  Glacial  times,  is  the  comparative  universality 
of  the  oscillations  then,  and  especially  their  coincidence  with  certain 
astronomical  changes,  which  greatly  increased  their  effect  upon  climate. 

Other  and  more  direct  methods  of  estimation,  however,  such  as  the 
recession  of  waterfalls  (p.  15)  and  of  lake-shores  and  the  extreme  fresh- 
ness of  glacial  scorings  and  polishings,  seem  to  indicate  a  much  shorter 
time  since  the  disappearance  of  the  ice-sheet.  This  is  again  a  strong 
reason  for  believing  that  geographical  changes  were  the  main  cause  of 
the  climate. 

3.  The  Quaternary  a  Period  of  Revolution — a  Transition  between 
the  Cenozoic  and  the  Modern  Eras. — We  have  already  seen  (pp.  282  and 
294)  that  between  the  great  eras,  and  perhaps  also  at  other  times,  there 
have  been  periods  of  oscillation  of  the  earth's  crust,  and  therefore  of 
changes  of  physical  geography,  marked  by  unconformity  of  strata;  and 
changes  of  climate,  marked  by  apparently  abrupt  changes  of  species. 
These  have  been  the  critical  periods  of  the  earth's  history — periods 
of  revolution  and  rapid  change.  But  for  that  very  reason  they  are 
also  pe/iods  of  lost  records.  We  have  already  spoken  of  the  lost  inter- 
val at  the  end  of  the  Archaean,  evidently  the  greatest  of  all ;  again,  of  a 
lost  interval  at  the  end  of  the  Palaeozoic,  partly  recovered  in  the  Per- 
mian, evidently  the  next  greatest ;  again,  of  a  lost  interval  at  the  end 
of  the  Cretaceous,  in  a  large  measure  recovered  in  the  Laramie  beds. 
There  are  doubtless  many  others  of  less  extent.  These  periods  are 
always  marked  by  unconformity  of  the  strata  and  change  in  the  life- 
system.  The  old  geologists  regarded  these  changes  as  sudden  and 
cataclysmic.  All  geologists  now  regard  the  suddenness  as  largely  ap- 
parent, and  the  result  of  lost  record. 

Now,  the  Quaternary  is  also  a  critical  period.  It  corresponds 
with  one  of  the  lost  intervals  ;  only,  in  this  case,  on  account  of  its  near- 
ness to  us,  the  record  has  been  recovered.  By  the  study  of  this  period, 
therefore,  we  may  hope  to  solve  many  problems  which  have  heretofore 
puzzled  us.  Here,  for  example,  we  have  oscillations  of  the  crust  on  a 
grand  scale,  producing  great  changes  of  physical  geography  and  cli- 
mate, and  therefore  of  fauna  and  flora.  Here  we  have  unconformity, 
now  being  produced  by  sedimentation  on  old  eroded  land-surfaces  in 
all  the  region  affected  by  the  oscillations — marine  sediments  in  fiords 
and  river  sediments  in.  old  river-channels.  But  we  observe  that  in  this 
case  these  effects  have  been  produced  slowly,  and  that  the  fauna  and 
flora  have  not  been  suddenly  destroyed  and  suddenly  recreated,  but 
have  continued  to  live  throughout,  the  species  gradually  changing. 
But,  what  is  still  more  interesting,  much  light  is  thrown  also  on  the 
hitherto  insoluble  problem  of  the  mode  and  the  cause  of  the  compara- 
tively rapid  change  of  species  in  these  critical  periods.  The  attentive 
study  of  the  Quaternary  shows  that,  in  addition  to  the  direct  effect  of 


SOME  GENERAL  OBSERVATIONS  ON  THE  WHOLE  QUATERNARY.  595 

change  of  climate,  one  great  cause  of  change  of  species  has  been  migra- 
tion :  migration  north  and  south,  enforced  by  change  of  temperature ; 
migration  in  any  direction,  permitted  by  change  of  physical  geography. 
This  point  is  so  important,  that  we  must  explain  it  somewhat  fully. 

It  will  be  remembered  (p.  507)  that  in  Miocene  times  Greenland, 
Iceland,  and  Spitzbergen,  were  covered  with  a  luxuriant  temperate 
vegetation.  The  congeners  of  their  vegetation  at  that  time  are  found 
now  in  California,  along  the  shores  of  the  Southern  Atlantic  States,  and 
in  Southern  Europe.  Evidently  at  that  time  there  was  no  polar  ice- 
cap, and  therefore  no  arctic  plants.  At  the  end  of  the  Pliocene,  the 
vegetation  shows  a  climate  not  greatly  differing  from  the  present.  It 
is  probable,  therefore,  that  the  cold  had  increased  until  an  ice-cap  had 
formed,  such  as  now  exists  in  polar  regions,  with  its  accompaniment 
of  arctic  species.  As  the  Glacial  epoch  came  on  and  culminated,  the 
polar  ice  slowly  extended — its  margin  crept  slowly  southward,  until 
it  reached  40°  in  America  and  50°  in  Europe,  with  local  extensions 
stretching  still  farther  southward,  in  mountain  regions.  The  southern 
polar  regions  were  probably  similarly  affected,  either  simultaneously  or 
alternately. 

We  must  not  confound  this  movement  southward  of  the  southern 
limit  of  the  ice  with  the  current  motion  of  the  ice-sheet  itself.  The 
limit  of  the  ice-cap  is  like  the  lower  limit  of  a  glacier  (p.  48).  It  may 
be  stationary,  or  advancing  or  retreating,  but  the  glacial  stream  flows 
ever  onward.  Again,  the  motion  of  a  glacial  current  is  slow — perhaps 
one  to  three  feet  per  day — but  the  extension  or  recession  of  the  glacial 
limit  is  far  slower,  perhaps  a  few  feet  per  annum.  We  may  thus  easily 
appreciate  the  immense  time  necessary  to  advance  this  limit  of  the  ice- 
cap to  40°  latitude. 

At  the  end  of  the  Glacial  and  the  commencement  of  the  Champlain 
epoch  a  movement  of  the  ice-limit  in  a  contrary  direction — a  retreat 
northward — commenced  and  continued,  with  perhaps  some  alternate 
progressions  and  regressions,  to  its  present  position. 

Now,  the  effect  of  this  advance  and  retreat  of  polar  ice  upon  plants 
and  animals  must  have  been  very  marked.  Temperate  plants,  inhabit- 
ing Greenland  in  the  Miocene,  were  pushed  to  the  shores  of  the  Gulf. 
Arctic  plants — i.  e.,  those  which  haunt  the  margin  of  perpetual  ice — 
were  pushed  to  Middle  United  States  and  to  Middle  Europe ;  and  arc- 
tic shells  were  similarly  driven  southward,  slowly,  generation  after  gen- 
eration. We  say  sloivly,  for  otherwise  they  must  have  been  destroyed. 
With  the  return  of  temperate  conditions,  and  the  retreat  of  the  ice- 
cap, these  species,  both  shells  and  plants,  again  went  northward  to  their 
appropriate  place.  But  the  plant  species,  and  some  land  invertebrate 
species,  such  as  insects,  had  an  alternative  which  the  shells  had  not, 
viz.,  to  seek  arctic  conditions  also  upward  on  mountains.  Many  did 


596  CENOZOIC   ERA— AGE   OF   MAMMALS. 

so  and  were  left  stranded  there.  Thus  is  explained  the  remarkable  fact 
that  Alpine  plant-species  in  Europe  are  similar  to  and  largely  identical 
with  those  in  America ;  and  both  with  the  present  arctic  species.  This 
indicates  a  former  wide  distribution  of  identical  arctic  species  all  over 
Europe  and  America,  and  their  subsequent  retreat  northward  into 
polar  regions  and  upivard  into  Alpine  isolation.  Grote  has  observed 
a  similar  isolation  of  Labrador  insect-species  on  Mount  Washington, 
and  on  the  Colorado  mountains.* 

There  was  probably  a  similar  movement,  to  a  less  extent,  of  temper- 
ate species.  In  the  Taxodium  of  the  Southern  Atlantic  and  Gulf 
swamps,  and  the  Sequoias  of  California,  we  doubtless  have  examples  of 
species  wide-spread  in  Miocene  times,  which  have  been  destroyed  by 
these  climatic  changes,  except  in  certain  limited  areas. 

But  plants  and  lower  species  of  animals  are  far  less  affected'  by 
changes  in  physical  conditions  than  are  the  higher  species  of  animals. 
This  is  shown  by  the  wide  range  both  in  space  and  time  of  the  former 
as  compared  with  the  latter.  Under  these  great  changes  and  enforced 
migrations,  therefore,  plants  and  invertebrate  animal  species  maintained 
their  specific  characters  mostly  unchanged,  or  but  slightly  changed. 
But  in  the  case  of  mammals  destruction  or  change  was  inevitable. 
Both  took  place — destruction  of  some  and  change  of  the  remainder. 

In  America  some  time  during  Quaternary,  perhaps  during  the 
period  of  northern  subsidence,  there  was  probably  a  broad  land-con- 
nection of  North  America  with  South  America  by  the  Caribbean  Sea 
region ;  and  certainly,  as  shown  by  the  similarity  of  plants,  with  North- 
ern Asia  by  the  region  between  the  Aleutian  Isles  and  Bering  Strait. 
Thus  migrations  were  not  only  enforced  by  climatic  changes,  but  per- 
mitted by  geographical  connections  with  adjacent  continents.  Also 
the  great  Pliocene  lake  1,000  miles  long  (p.  505)  which  separated  West- 
ern from  Eastern  North  America  was  abolished,  and  migrations  became 
freer  between  the  East  and  West.  It  is  evident  that  from  all  these 
causes  mammalian  faunas  from  widely-different  regions  were  precipi- 
tated upon  each  other,  and  struggled  together  for  mastery.  Large 
numbers  of  species  were  destroyed,  and  the  fittest  only  survived,  and 
these  only  under  changed  forms.  It  is  quite  possible  that  man  came 
to  America  with  the  Asiatic  mammalian  invasion.  If  so,  his  earliest 
remains  in  America  may  be  looked  for  on  the  Pacific  coast. 

Of  course,  we  use  the  word  migrations  in  its  widest  sense,  as  change 
of  habitat  of  species  as  well  as  of  individuals.  In  the  case  of  plants 
and  many  lower  animals,  the  place  of  species  only  moved  slowly  from 
generation  to  generation.  In  the  case  of  mammals  there  was  more  de- 
cided movement  of  individuals. 


*  American  Journal  of  Science,  1875,  vol.  x,  p.  335. 


SOME   GENERAL  OBSERVATIONS  OX  THE  WHOLE  QUATERNARY.  597 

This  very  important  subject  has  been  more  closely  studied  in  Europe 
than  here,  although  we  believe  that  America  is  the  simplest  and  best 
field  for  its  elucidation.  During  the  Quaternary  probably  at  least  four 
distinct  mammalian  faunas  struggled  together  for  mastery  on  European 
soil :  1.  The  Pliocene  autochthones.  2.  Invasions  from  Africa,  per- 
mitted by  geographical  connection  opening  a  gateway  through  the 
Mediterranean,  since  closed.  3.  Invasions  from  Asia,  by  opening  of  a 
gateway  which  has  remained  open  ever  since ;  with  this  invasion  prob- 
ably came  man.  4.  Invasions  from  arctic  regions.  Probably  more  than 
one  such  invasion  took  place ;  certainly  one  occurred  during  the  second 
Glacial  epoch,  called  on  that  account  the  Reindeer  period. 

The  final  result  of  all  this  struggle  was,  that  the  Pliocene  autoch- 
thones were  destroyed  or  driven  southward  in  Africa;  the  southern 
species  were  mostly  destroyed  or  driven  back  with  changed  forms  and 
diminished  size ;  the  northern  species,  reindeer,  glutton,  etc.,  retreated 
again  northward,  and  the  Asiatics  remained  in  possession  of  the  field, 
but  greatly  changed  by  the  struggle.  Man  was  among  these,  and  cer- 
tainly one  of  the  principal  agents  in  the  change.  Speaking  more  ac- 
curately, the  present  fauna  of  Europe  may  be  said  to  be  a  product  of 
all  these  factors ;  but  the  Asiatic  invasion  seems  to  be  the  largest  factor. 

Thus,  then,  the  gradual  progress  of  evolution  through  all  geological 
time,  and  the  causes  of  the  phenomenon  of  rapid  change  of  species  at 
critical  periods  of  the  earth's  history,  may  be  briefly  summarized  as 
follows : 

1.  A  gradual,  extremely  slow  evolution  of  organic  forms  under  the 
operation  of  all  the  forces  and  factors  of  evolution  known  and  un- 
known, whatever  we  may  conceive  these  to  be.     This  cause  acting 
alone  would  produce  gradual  changes  in  time  (geological  faunas),  but 
without  geographical  diversity. 

2.  This  slow  evolution  takes  different  directions  in  different  places 
and  under  different  physical  conditions,  and  thus  gives  rise  to  geo- 
graphical faunas  and  floras.     Such  geographical  faunas  and  floras, 
if  isolated  by  physical  barriers,  become  more  and  more  diverse  so  long 
as  the  barriers  are  maintained.     This  cause  acting  alone  would  produce 
extreme  geographical  diversity,  and  render  determination  of  synchro- 
nism impossible. 

3.  During  critical  periods  physical  changes  and  consequent  migra- 
tions, partly  enforced  by  changes  of  climate,  partly  permitted  by  re- 
moval of  barriers,  and  the  precipitation  of  adjacent  faunas  and  floras 
upon  each  other,  and  the  cons  .»quent  severe  struggle  for  life,  give  rise 
to  far  more  rapid  changes  of  species,  but  at  the  same  time  to  greater 
geographical  uniformity.     This  more  rapid  change  of  organic  forms 
is  produced  partly  by  severer  pressure  of  external  conditions,  certainly 
one  factor  of  change ;  partly  by  severer  struggle  for  life,  certainly  an- 


598  CENOZOIC   ERA— AGE   OF  MAMMALS. 

other  factor  of  change ;  and  doubtless  partly  also  by  the  more  active 
operation  of  other  factors  of  change,  which  we  do  not  yet  understand. 
This  last  cause  tends  to  produce  not  only  more  rapid  general  evolution, 
but  also  to  destroy  extreme  geographical  diversity ;  and  since  it  oper- 
ates on  animals  rather  more  than  plants,  plant  species  are  more  apt  to 
be  local,  and  are  less  certainly  carried  along  with  the  stream  of  general 
evolution,  and  are,  therefore,  less  reliable  in  determining  geological  age 
than  animals. 

4.  Re-isolations  in  new  positions.  This  would  again  produce  diver- 
gence of  geographical  faunas  and  goras  increasing  with  time,  as  long 
as  the  isolation  continued.  Thus  it  is  seen  that  geographical  diversity 
is  a  product  of  three  factors — viz.,  difference  of  environment ;,  isolation, 
and  time. 

The  last  of  these  critical  periods  was  the  Quaternary.  Therefore  in 
the  changes  of  physical  geography  and  climate  of  this  period  we  find 
the  main  cause  of  the  present  distribution  of  species  ;  and,  conversely, 
this  distribution  furnishes  the  key  to  the  geographical  changes  and  the 
direction  of  migrations  during  the  Quaternary. 

The  principles  enumerated  above  are  so  important,  that  some  ex- 
amples illustrating  seem  necessary. 

1.  Australia. — The  fauna  and  flora  of  Australia  are  the  most  pe- 
culiar known  anywhere.    Confining  our  attention  to  mammals ;  of  about 
one  hundred  and  thirty  species  known  in  Australia,  all  except  two  or 
three  bats  and  rats  (of  all  animals  the  most  likely  to  be  accidentally 
introduced)  are  non-placentals,  i.  e.,  marsupials  and  monotremes.    And, 
moreover,  with  the  exception  of  several  opossums  in  America,  North 
and  South,  non-placentals  are  not  found  anywhere  except  in  Aus- 
tralia and  neighboring  islands.     The  explanation  is  as  follows  :  Of  all 
countries,  Australia  has  been  the  longest  isolated  from  all  other  conti- 
nents.    The  wide  migrations  of  the  Quaternary  which  mingled  the 
faunas  and  floras  of  other  continents  did  not  reach  this  one.     It  will 
be  remembered  that,  in  Jurassic  times,  marsupials  in  great  numbers 
inhabited  Europe  and  America,  and  doubtless  all  other  great  conti- 
nents, Australia  among  the  number.     It  will  be  remembered  also  that 
true  placental  mammals  were  not  introduced  until  the  Tertiary.     It  is 
evident,  then,  that  Australia  was  separated  before  the  Tertiary,  and  has 
been  isolated  ever  since.     The  severe  struggle  which  determined  the 
evolution  of  placentals  elsewhere  did  not  effect  that  continent.     Pla- 
centals  were  not  evolved  there,  nor  could  they  get  there  from  abroad. 

2.  Africa. — The  mammalian  fauna  of  Africa,  south  of  Sahara,  as 
shown  by  Wallace  (Island  Life),  consist  of  two  very  distinct  groups— 
viz.,  a  group  of  small  animals  of  very  generalized  type — insectivores  and 
lemurs ;  and  a  group  of  large,  powerful,  and  highly-specialized  animals 
— carnivores  and  herbivores.     The  animals  of  the  former  group  are 


SOME  GENERAL  OBSERVATIONS  ON  THE  WHOLE  QUATERNARY.  599 

peculiar  to  Africa  and  Madagascar,  and  are  probably  indigenous ;  the 
animals  of  the  latter  group  are  similar  to  the  Pliocene  animals  of  Eu- 
rasia, and  are  probably  invaders.  The  explanation  is  as  follows : 
During  late  Tertiary  times,  Africa  was  separated  from  Eurasia  prob- 
ably by  a  sea,  and  inhabited  only  by  the  group  which  we  called  in- 
digenes. Then  came  the  Glacial  oscillations,  which  opened  a  gateway 
into  Africa,  and  the  concomitant  climatic  changes  which  drove  the 
Eurasian  Pliocene  animals  southward.  These  invaders  soon  domi- 
nated the  weaker  indigenes  and  were  subsequently  isolated  in  their 
new  home.  The  struggle  which  followed  has  produced  considerable 
change  in  both  groups,  but  especially  in  the  indigenes. 

3.  Madagascar. — The  mammalian  fauna  of  Madagascar  is  very  re- 
markable ;  nearly  all  the  species  being  peculiar  to  that  island.     There 
is,  however,  a  general  resemblance  to  the  indigenes  of  Africa.     The 
explanation  is  as  follows :  During  Tertiary  times,  Madagascar  was  a 
part  of  the  African  Continent,  and  both  inhabited  by  the  same  animals, 
viz.,  the  indigenes.     But  in  Pliocene  times,  before  the  northern  inva- 
sion, it  was  separated,  and  therefore  the  invasion  did  not  reach  it. 
Meanwhile  by  long  isolation,  the  Malagasian  fauna  changed  slowly  to 
its  present  state,  but  the  change  was  not  so  great  as  in  their  African 
congeners,  who  had  to  bear  the  brunt  of  the  struggle  with  invaders. 
Therefore,  we  have  in  the  Malagasian  fauna  a  somewhat  nearer  ap- 
proach to  the  Tertiary  fauna  of  both. 

4.  British  Isles. — The  fauna  and  flora  of  the  British  Isles  are  almost 
but  not  quite  identical  with  those  of  Europe.     Between  the  two  there 
are  strong  varietal  but  not  specific  differences.     They  are  also  some- 
what less  rich,  some  species  being  wanting  which  are  found  on  the 
continent.     This  is  especially  true  of  Ireland.     The  explanation  is  as 
follows :  The  climatic  changes  of  the  Glacial  epoch,  and  especially  the 
submergence  of  the  Champlain  (Fig.  942)  completely  destroyed  the 
indigenous  species  of  these  islands.     But,  during  the  Terrace,  they 
were  again  broadly  connected  with  the  continent,  and  therefore  colo- 
nized by  continental  species.     They  have  been  again  separated,  and 
divergence  of  organic  forms  has  again  commenced  ;  but  the  period  of 
connection  was  so  brief  that  the  colonization,  especially  in  the  extreme 
parts,  was  not  completed  before  re-isolation ;  and  the  time  since  re- 
isolation  has  been  too  short  for  the  divergence  to  go  very  far ;  it  has 
reached  only  varietal  differences. 

5.  Coast  Islands  of  California. — Along  the  coast  of  the  southern 
part  of  California  there  is  a  string  of  bold,  rocky  islands,  two  thousand 
feet  high,  and  about  fifty  miles  off  shore.     The  flora  of  these  islands, 
as  shown  by   Prof.  Greene,*  is  very  remarkable.      Of  nearly  three 

*  Bulletin  of  the  California  Academy  of  Sciences,  No.  7. 


600  CENOZOIC   ERA— AGE   OF   MAMMALS. 

hundred  species  found  there,  about  fifty  are  entirely  peculiar — being 
found  nowhere  else  in  the  world.  Of  the  others,  all  are  characteristic 
California  species.  Now  for  the  explanation :  During  late  Tertiary 
and  early  Quaternary  times  the  continent  was  higher  than  now,  and 
these  islands  were  a  part  of  California.  We  have  already  given  proof 
of  this  fact  on  page  562.  During  that  time  California,  including  these 
islands,  was  occupied  by  a  flora  not  greatly  different  from  that  of  the 
islands  now.  By  the  oscillations  of  the  Quaternary  the  islands  were 
separated.  Then  came  the  northern  invasion  of  -species,  changing 
some  of  the  native  species  and  destroying  others,  and  forming  the  Cali- 
fornia flora  of  to-day.  The  islands  were  spared  this  invasion  by  isola- 
tion. It  is  probable,  therefore,  that  in  the  island  flora  we  have  a  some- 
what near  approach  to  the  flora  of  California  before  the  invasion.* 

Thus,  then,  regarding  the  Oenozoic  and  the  Modern  as  consecutive 
eras,  and  the  Quaternary  as  the  transitional,  revolutionary,  or  critical 
period  between,  we  see  a  great,  and,  if  we  had  lost  the  Quaternary,  an 
apparently  sudden,  change  of  species.  Yet  this  change,  as  great  as  it 
is,  is  not  to  be  compared  in  magnitude  with  that  which  separates  the 
great  eras  or  even  ages  from  each  other.  Evidently,  therefore,  we  must 
regard  the  lost  interval  between  the  Archaean  and  Palaeozoic,  and  that 
between  the  Palaeozoic  and  Mesozoic,  yes,  even  that  between  the  Meso- 
zoic  and  Cenozoic  (as  small  as  this  latter  is  in  comparison  with  the 
others),  as  all  of  them  far  greater  than  the  whole  Quaternary  period  ; 
or  else  the  forces  of  evolution  must  have  been  far  more  active  in  those 
earlier  times  than  more  recently. 

4.  Drift  in  Relation  to  Gold. — We  have  already  stated  (p.  240)  that 
gold  occurs  in  two  positions,  either  in  quartz- veins  intersecting  meta- 
morphic  slates  (quartz-mines)  or  in  drift-gravels  (placer-mines).  The 
auriferous  slates  may  be  of  various  ages.  In  the  Appalachian  chain, 
and  in  the  Ural  Mountains,  and  in  Australia,  the  slate  or  schist  is 
metamorphic  Silurian.  In  California  it  is  Jura-  Trias.  The  placer 
gold  deposits  are  everywhere  Quaternary  drift-gravels. 

There  has  been  throughout  all  geological  time  a  progressive  con- 
centration of  gold,  as  well  as  many  other  metals,  in  a  more  and  more 
available  form  :  1.  It  was  first  disseminated  in  excessively  small  quan- 
tities, too  small  to  be  detected,  through  the  slates,  derived  doubtless 
from  the  sea,  in  the  waters  of  which  it  is  detectable  in  very  small  quan- 
tities. 2.  After  the  upheaval,  crumpling,  metamorphism,  and  fissuring 
of  these  slates,  the  gold  was  dissolved,  and  accumulated,  along  with 
silica  and  metallic  sulphides,  in  these  fissures,  as  auriferous  veins.  3. 
Atmospheric  agencies  acting  on  these  outcropping  veins  dissolved  away 
the  sulphides,  and  left  the  gold  in  a  still  more  available  form  along  the 

*  American  Journal  of  Science,  vol.  xxxiv,  p.  457,  1887. 


SOME  GENERAL  OBSERVATIONS  ON  THE  WHOLE  QUATERNARY.  601 

backs  of  the  veins.  4.  Then  came  the  ice-sheet  and  the  glaciers  of 
the  Quaternary,  like  a  plow,  cutting  away  the  backs  of  the  quartz- 
veins,  together  with  the  containing  slates,  and,  like  a  mill,  grinding  all 
to  gravel,  and  heaping  it  away  in  moraines.  Some  of  the  placer-mines 
are  in  these  moraines,  but  most  of  the  gold  has  been  subjected  to  still 
another  process.  5.  Lastly,  in  the  Champlain  epoch,  the  river-floods 
washed  these  moraine  heaps  down  the  rivers,  sorting  them  and  deposit- 
ing where  the  velocity  of  the  current  diminished.  These  river-gravels, 
thus  sorted,  cradled,  panned  by  the  action  of  currents,  and  therefore 
with  the  coarse  gold  near  the  bottom  and  high  up  the  gulches,  consti- 
tute the  richest  placer-mines. 

The  placers  of  California,  however,  are  of  two  kinds,  viz.,  the  ordi- 
nary or  superficial  placers,  and  the  deep  placers.  The  superficial  placers 
are  gravel-drifts  in  the  present  river-beds.  The  deep  placers  are  gravel- 
drifts  in  old  river-beds.  These  old  river-beds,  as  already  stated  (pp. 
248,  567),  are  in  many  cases  covered  up  with  lava.  Usually  the  general 
direction  of  the  old  bed  coincides  with  that  of  the  present  river-system, 
but  sometimes  the  present  river-system  cuts  across  the  old  river-system. 
In  all  cases,  however,  it  is  evident  that  the  old  river-gravels  were 
formed  before  the  lava-flow,  and  the  newer  gravels  after  the  lava-flow. 
In  all  cases  also  the  present  river-system  has  cut  down  far  below  the 
old  beds,  in  this  respect  entirely  different  from  the  old  river-beds  of  the 
eastern  portion  of  the  continent.  The  reason  of  this  has  already  been 
explained  (p.  567). 

The  following  figures  are  ideal  sections  altered  a  little  from  Whit- 
ney's :  Fig.  965,  of  a  case  in  which  the  old  and  the  present  river-beds 
are  parallel  to  each  other ;  Fig.  966,  where  the  latter  cut  through  the 
former.  In  the  former  case  the  section  is  across  the  lava-flow,  as  well 
as  across  the  river-beds ;  in  the  latter  case  it  is  in  the  direction  of  the 
lava-flow,  and  therefore  of  the  old  river-bed,  but  across  the  present 
river-bed. 

In  Fig.  965,  which  is  a  section  across  Table  Mountain,  in  Tuolumne 
County,  California,  L  is  the  lava-cap,  140  feet  thick,  beneath  which  is 


FIG.  965.— Section  across  Table  Mountain.  Tuolnmne  Connty.  California:  L,  lava;  G,  gravel;  S, 
slate;  R,  old  river-bed;  R',  present  river-bed. 

the  old  river-bed,  7?,  with  its  gravel,  (7,  now  worked  by  a  tunnel,  driven 
through  the  rim-slate  S.    More  recent  gravels,  G',  are  seen  in  the  pres- 


602 


CENOZOIC   ERA— AGE   OF   MAMMALS. 


ent  river-beds,  R'.     In  this  locality  G  represents  the  deep  placers,  and 
O'  the  superficial  placers. 

The  history  of  changes  shown  in  these  sections  is  sufficiently  obvi- 
ous. In  the  time  of  the  old  river-system,  R  was  a  river-bed,  doubtless 
with  a  ridge  on  either  side  represented  by  the  dotted  lines.  In  this 
bed  accumulated  gravel,  containing  gold.  Then  came  the  lava-flow, 
which  of  course  ran  down  the  valley,  displacing  the  river  and  covering 
up  the  gravels.  The  displaced  rivers  now  ran  on  either  side  of  the 
resistant  lava,  and  cut  out  new  valleys,  2,000  feet  deep,  in  the  solid 
slate,  leaving  the  old  lava-covered  river-beds  and  their  auriferous  gravels 
high  up  on  a  ridge.  The  deeper  cutting  was  the  result  of  the  higher 
slope.  In  other  cases  the  convulsion  which  ejected  the  lava  also 
changed  greatly  the  direction  of  the  slope  of  the  country,  ajid  there- 
fore the  direction  of  the  streams.  In  such  cases  of  course  the  present 
river-system  cuts  across  the  old  river-beds  and  gravels,  and  their  cover- 
ing lavas,  as  shown  in  Fig.  966. 


FIG.  966.— Lava-Stream  cut  through  by  Rivers:  a,  a,  basalt;  b,  b,  volcanic  ashes;  c,  c.  Tertiary; 
d,  d,  Cretaceous  rocks:  R,  R,  direction  of  the  old  river-bed;  R',  R',  sections  of  the  present 
river-beds  (from  Whitney). 

Age  of  the  River-Gravels. — The  age  of  the  old  river-gravels  is  still 
doubtful ;  that  of  the  newer  river-gravels  is  undoubtedly  Champlain  or 
early  Terrace.  Below  we  give  a  list,  taken  from  Whitney,  of  the  re- 
mains found  in  these  gravels  : 


Newer  placers. 


Deep  placers. 


Great  mastodon. 

Mammoth. 

Bison. 

Tapir,  modern. 

Horse,  modern. 

Man's  works. 

Great  mastodon.* 

Mammoth. 

Mylodon. 

Tapir,  modern. 

Rhinoceros  (ally). 

Hippopotamus  (ally). 

Camel  (ally). 

Horse,  extinct  species. 


It  will  be  seen  that  the  fauna  of  the  deep  placers  unite  Pliocene 
and  Quaternary  characters.  The  great  mastodon,  the  mammoth,  the 

*  Whitney  states  (Geological  Survey  of  California,  vol.  i,  p.  252)  that  neither  the 
mastodon  nor  the  mammoth  is  found  in  deep  placers ;  but  both  have  since  been  found 
there. 


PSYCHOZOIC  ERA— AGE  OF  MAN— RECENT   EPOCH.  6Q3 

tapir,  and  mylodon,  are  distinctively  Quaternary,  while  the  others  are 
Pliocene.  The  plants,  according  to  Lesquereux,  are  decidedly  Pliocene. 
Therefore  Whitney  has  not  only  put  the  deep  placers  in  the  Pliocene, 
but  made  them  the  representatiye  of  the  whole  Pliocene,  and  probably 
Miocene,  and  the  lava-flow  as  the  dividing-line  between  the  Tertiary 
and  Quaternary.  But,  all  the  facts  considered,  it  seems  most  probable 
that  both  the  filling  of  the  old  river-beds,  and  their  protection  by  lava, 
took  place  comparatively  rapidly,  and  were  together  the  closing  scene 
of  the  Tertiary  drama.  The  deep  gravels,  therefore,  may  be  placed 
indifferently  in  the  latest  Pliocene  or  earliest  Quaternary.  The  newer 
gravels  are  undoubtedly  Quaternary  and  recent.  Certain  it  is  that  the 
deep  placer-gravels  are  similar  in  all  respects  to  the  Quaternary  gravels 
all  over  the  world,  except  that,  by  percolating  alkaline  waters  contain- 
ing silica,  they  have  been  cemented  in  some  cases  into  grits  and  con- 
glomerates. This  is  because  they  are  covered  with  lava  which  yields 
both  the  alkali  and  the  soluble  silica,  as  already  explained  (p.  248). 

In  any  case,  we  have  here  an  admirable  illustration  of  the  immen- 
sity of  geological  times.  The  whole  work  of  cutting  the  hard  slate- 
rock  2,000  feet  or  more  has  been  done  since  the  lava-flow,  and  therefore 
certainly  since  the  beginning  of  the  Quaternary.  But  it  is  necessary 
to  remember  that,  on  account  of  the  high  slope  of  the  new  river-beds, 
the  work  was  exceptionally  rapid. 


CHAPTER  VI. 
PSYCHOZOIC  ERA— AGE  OF  MAN— RECENT  EPOCH. 

Characteristics. — The  Quaternary,  and,  indeed,  all  previous  ages, 
were  reigns  of  brute  force  and  animal  ferocity.  A  condition  of  things 
prevailed  which  was  inconsistent  with  the  supremacy  of  man.  The  age 
of  man,  on  the  contrary,  is  characterized  by  the  reign  of  mind.  There- 
fore, as  was  necessary,  the  dangerous  animals  decreased  in  size  and 
number,  and  the  useful  animals  and  plants  were  introduced,  or  else 
preserved  by  man. 

Distinctness  of  this  Era. — In  regard  to  the  distinctness  and  impor- 
tance of  this  era,  there  are  two  views  which  will  probably  ever  divide 
geologists,  depending  on  the  two  views  regarding  the  relation  of  man 
to  Nature.  From  the  purely  structural  and  animal  point  of  view,  man 
is  very  closely  united  with  the  animal  kingdom.  He  has  no  department 
of  his  own,  but  belongs  to  the  vertebrate  department,  along  with  quad- 
rupeds, birds,  reptiles,  and  fishes.  He  has  no  class  of  his  own,  but  be- 


60± 


PSYCHOZOIC   ERA— AGE   OF  MAN— RECENT   EPOCH. 


longs  to  the  class  Mammalia,  along  with  quadrupeds.  Neither  has  he 
an  order  of  his  own,  but  belongs  to  the  order  of  Primates,  along  with 
monkeys,  lemurs,  etc.  Even  a  family  of  his  own,  the  Hominidw,  is 
grudgingly  admitted  by  some.  But  from  the  psychical  point  of  view 
it  is  simply  impossible  to  overestimate  the  space  which  separates  man 
from  all  lower  things.  Man  must  be  set  off  not  only  against  the 
animal  kingdom,  but  against  the  whole  of  Nature  besides,  as  an 
equivalent :  Nature  the  book  —  the  revelation  —  and  man  the  inter- 
preter. 

So  in  the  history  of  the  earth  :  from  one  point  of  view  the  era  of 
man  is  not  equivalent  to  an  era,  nor  to  an  age,  nor  to  a  period,  nor  even 
to  an  epoch.  But  from  another  point  of  view  it  is  the  equivalent  of 
the  whole  geological  history  of  the  earth  besides.  For  the  history  of 

the  earth  finds  its  consummation,  and  its  interpreter, 

and  its  significance,  in  man. 

But  there  is   still   another  and  perhaps  a  better 

reason  for  making  this  a  primary  division.    There  is 

now  going  on  under  our  eyes,  and  by  the  agency  of 


FIG.  967.— Dinornis  giganteps,  x  -fa  (from  a  pho-       FIG.  968.— Aptornis  didifonnis,  x  &  (from   a 
tograph  of  a  skeleton  in  Christchurch  Mu-  photograph  cf  a  skeleton  in  Christchurch 

seum,  New  Zealand).  Museum,  New  Zealand). 

man,  a  change  of  fauna  and  flora  as  sweeping,  and  far  more  rapid, 
than  any  which  has  ever  taken  place  in  the  history  of  the  earth.  We 
do  not  sufficiently  appreciate  this,  only  because  we  are  in  the  midst  of 


PSYCHOZOIC   ERA— AGE   OF   MAX— RECENT   EPOCH. 


605 


it.     The  change  will  be  completed  when  civilized  man  dominates  the 
whole  earth. 

The  rocks  of  this  epoch  are  the  present  river-deposits,  lake-deposits, 
sea-deposits,  volcanic  ejections,  etc.,  already  treated  of  in  Part  I.  The 
fauna  and  flora  of  this  epoch  are  the  species  still  living  on  the  earth. 
These  are  different  from  those  of  the  Tertiary,  and  largely  from  those 
of  the  Quaternary,  times ;  but  the  change,  as  we  have  already  shown, 
has  been  gradual,  not  sudden;  man  himself  being  one  of  the  chief 
agents  of  change. 

The  Change  still  in  Progress— Examples  of  Recently-Extinct  Species. 
—The  gradual  change  of  fauna  has  been  going  on  through  many  ages, 
and  is  still  going  on  under  our  eyes.      Many  remarkable 
Quaternary  species  have  lingered,  and  become  extinct  by 
the  agency  of  man,  even  in  historic  times.     Among  the 
most  remarkable  of  these  are  the  huge  wingless  birds,  the 
remains  of  which  have  been  discovered  in  New  Zealand, 
Madagascar,  and  Mauritius,  viz.,  the  Dinornis  (huge  bird), 
(tall  bird),  Palapteryx  (old  wingless  bird),  the 
Solitaire,  and  the   Dodo.     Through  the  kindness  of  Mr. 

C.  D.  Voy,  I  am  able  to  give 
good  figures  of  the  skeletons 
of  several  of  these  extraor- 
dinary-extinct birds,  taken 
from  photographs  (Figs. 
9G7,  9G8). 

The  Dinornis  giganteut 
of  New  Zealand,  and  the 
jfflpiornis  of  Madagascar, 
were  probably  twelve  feet 
high.  The  tibia  of  the 
former  has  been  found  near- 
ly a  yard  long,  and  as  thick 
as  the  tibia  of  a  horse>  and 
the  egg  of  the  latter,  well 
preserved,  thirteen  inches 
long  and  nine  inches  in  di- 
ameter, with  a  capacity  of 
two  gallons.  The  toe-bones 
of  the  D.  elephantopus  (Fig.  9G9)  rivaled  in  size  those  of  the  elephant 
(Owen).  These  huge  birds  must  have  been  capable  of  making  tracks 
nearly  as  large  as  those  of  the  supposed  birds  of  the  Connecticut  Valley 
sandstone  (p.  455).  Such  tracks  have  indeed  been  recently  found  in 
New  Zealand,  in  a  very  soft  sandstone.  The  Dodo,  of  Mauritius,  a 
heavy,  clumsy  bird,  of  fifty  pounds'  weight,  with  loose,  do'wny  feathers, 


FIG.  969.— Dinornis  elephantopus,  x  ^  (after  Owen). 


606 


PSYCHOZOIC   ERA— AGE   OF   MAN— RECENT  EPOCH. 


and  imperfect  wings,  like  a-  new-born  chicken,  became  extinct  only  about 
150  or  200  hundred  years  ago.  The  Apteryx,  to  which  of  all  living  birds, 
the  Dinornis,  Aptornis,  etc.,  are  most  nearly  allied,  still  survives,  ready 
to  disappear  (Fig.  970). 

The  Bos  primigenius,  the  gigantic  ox  of  Quaternary  times,  is  sup- 
posed to  be  the  same  as  ths  Urus  of  Caesar,  and  therefore  became  ex- 


FIG.  970.— Apteryx  Australis. 

tinct  since  Roman  times.  The  Quaternary  bison  of  Europe  would 
have  been  now  entirely  extinct,  but  for  the  imperial  edict  which  pre- 
serves a  few  in  the  forests  of  Lithuania.  The  lion,  the  tiger,  the  bison, 
the  elephant,  and  the  rhinoceros,  and,  in  fact,  all  the  fiercer  and  larger 
animals,  are  even  now  disappearing  before  the  advance  of  civilized  man. 
Thus,  in  passing  from  geological  to  present  times  we  trace  rocks 
into  sediments  and  soils ;  geological  agencies  into  chemical  and  physi- 
cal agencies,  now  in  operation ;  extinct  faunas  and  floras  into  the  liv- 
ing fauna  and  flora  ;  in  a  word,  geology  into  chemistry  and  physics,  and 
paleontology  into  zoology  and  botany. 


ANTIQUITY   OF   MAN.  607 

Now,  in  this  gradual  change  of  fauna,  when  did  man  first  appear 
upon  the  scene,  and  what  was  the  character  of  primeval  man  ?  This 
introduces  us  to  two  very  important  but  very  difficult  and  obscure  sub- 
jects. 

I. — ANTIQUITY  OF  MAX. 

On  this  interesting  subject  the  three  sciences — History,  Archaeology, 
and  Geology — meet  and  co-operate ;  and  the  recent  rapid  advance  has 
been  the  result  of  this  union,  and  especially  of  the  application  of  geo- 
logical methods  of  research. 

Archaeologists  have  long  ago  divided  the  history  of  human  civiliza- 
tion into  three  epochs  or  ages,  named,  from  the  materials  of  which 
weapons  and  tools  are  made,  respectively  the  Stone  age,  the  Bronze 
age,  and  the  Iron  age.  We  are  here  concerned  only  with  the  Stone 
age ;  the  others  belong  to  history. 

Closer  study  has  again  divided  the  Stone  age  into  two,  viz.,  the 
Palaeolithic  (old  Stone  age)  and  the  Neolithic  (newer  Stone  age). 
During  the  former,  only  chipped  stone  implements  were  used ;  while 
in  the  latter  polished  stone  implements  were  also  used.  It  is  princi- 
pally with  the  Palaeolithic  that  we  are  here  concerned. 

Still  closer  study,  in  connection  with  geology,  has  again  divided  the 
Palaeolithic  into  an  earlier  and  a  later.  The  earlier,  being  contempora- 
neous with  the  mammoth,  is  called  the  Mammoth  age  ;  and  the  latter, 
for  similar  reasons,  the  Reindeer  age.  The  mammoth,  however,  existed 
also  in  this  latter  age.  The  former  seems  to  correspond  with  the 
Champlain  or,  perhaps,  interglacial  epoch  in  geology,  for  these  are 
often  confounded,  and  the  latter  with  the  Terrace  of  America,  or  Sec- 
ond Glacial  epoch  of  Europe.  The  Neolithic  commences  the  Psycho- 
zoic  era,  or  reign  of  man — the  period  when  man  had  established  his 
supremacy.  The  following  table  expresses  these  views  : 

3.  Iron  age } 

2.  Bronze  age j.  Psychozoic  era. 

{Neolithic — Domestic  animals.  ) 
PaiowiiutTn  J  Reindeer  age    =  Terrace  or  perhaps  Second  Glacial  epoch. 
c'  }  Mammoth  age  =  Champlain  epoch  or  perhaps  interglacial. 

These  divisions  and  their  relations  to  geological  epochs  have  been 
established  in  Europe.  They  would  probably  apply  also  to  some  parts 
of  Asia  and  Africa,  for  in  portions  of  these  old  countries  man  has 
doubtless  passed,  successively  and  slowly,  through  all  these  stages.  But 
all  these  stages  are  not  represented  in  all  countries,  nor  do  they  neces- 
sarily correspond  to  the  geological  epochs  mentioned  above.  The  South- 
Sea-Islanders,  for  example,  are  still  in  the  Stone  age.  The  American 
Indians  were  in  the  Stone  age  only  three  centuries  ago. 

The  table  given  above  carries  man  back  to  the  Champlain  or  even 


608 


PSYCHOZOIC  ERA— AGE   OF   MAN— RECENT   EPOCH. 


the  interglacial  epoch.  There  are  some  geologists  who  think  they  find 
evidence  of  a  much  earlier  existence  of  man.  We  will,  therefore,  very 
rapidly  review  the  evidences  of  the  antiquity  of  man.  In  doing  so, 
however,  we  shall  accept  none  but  thoroughly  reliable  evidence.  There 
has  been  recently  far  too  much  eagerness  to  find  facts  which  overthrow 
accepted  beliefs,  and  to  accept  them  on  this  account  alone.  We  will 
take  up  European  localities  first,  because  the  subject  has  been  more 
carefully  studied  there. 

Primeval  Man  in  Europe. 

Supposed  Miocene  Man — Evidence  unreliable. — The  earliest  period 
in  the  strata  of  which  any  supposed  evidences  of  the  existence  of  man 

have  been  found  is  the  Mio- 
cene. These  evidences, 
however,  are  confessedly 
meager,  and  by  all  careful 
investigators  considered  un- 
reliable. Some  flint-flakes 
(Fig.  971),  so  rough  that 
they  may  be  the  result  of 
physical  instead  of  intelli- 
gent agencies ;  some  bones 
of  animals,  marked  with 
parallel  scratches,  as  if 
scraped,  but  the  scratches 
may  have  been  produced  by 
currents,  or,  as  Lyell  thinks, 
by  the  teeth  of  Kodents ; 
some  more  positive  evi- 
dences of  man's  agency, 
but  in  strata  of  doubtful 
age,  or  else  the  result  of 
accidental  mixture  not  con- 
temporaneous with  the  de- 
posit itself  —  such  is,  in 
brief,  the  evidence.  The 
Miocene  man  is  not  ac- 
knowledged by  a  single 
careful  geologist.  Mortillet 
thinks  that  there  may  have  existed  in  Miocene  times  a  tool-making 
animal,  but  not  true  man. 

Supposed  Pliocene  Man. — The  evidence  of  the  existence  of  man 
during  the  Pliocene  period  is,  if  possible,  still  more  meager  and  unre- 
liable. M.  Hamy  thinks  he  has  found  undoubted  evidence  of  human 


FIG.  971.— Flint  Flakes  collected  by  Abbe  Bourgeois  from 
Miocene  Strata  at  Thenay  (after  Gaudry).    Natural  size. 


PRIMEVAL   MAN   IN  EUROPE.  609 

agency  in  flint  implements  in  Pliocene  strata  at  Savone ;  but  the  con- 
temporaneousness of  the  flints  and  the  deposit  is  regarded  as  doubtful. 
Again,  Palaeolithic  implements  have  been  found  in  Madras  in  strata 
supposed  by  Falconer  to  be  Pliocene ;  but  more  recent  investigations 
make  the  strata  Quaternary.*  Of  the  supposed  Pliocene  man  in  Cali- 
fornia we  will  speak  further  on.  Suffice  it  to  say  that  Dawkins,  sum- 
ming up  the  evidence  in  1882,f  Boule  in  1888,J  and  Evans  in  1890,* 
decide  that  the  existence  of  Tertiary  man  is  yet  unproved. 

Quaternary  Man— Mammoth  Age. — But  of  the  existence  of  man  in 
Europe  and  America,  as  early  as  the  middle  of  the  Quaternary  period, 
there  seems  to  be  abundant  evidence.  We  shall  select  only  a  few 
striking  examples : 

a.  In  River-Gravels. — In  the  terraces  of  the  river  Somme,  near 
Abbeville,  were  found,  nearly  twenty  years  ago,  by  M.  Boucher  de 
Perthes,  chipped  flint  implements,  associated  with  bones  of  the  mam- 
moth, rhinoceros,  hippopotamus,  hyena,  horse,  etc.  The  doubts  with 


FIG.  972.— Section  across  Valley  of  the  Somme:  1,  peat,  twenty  to  thirty  feet  thick,  resting  on 
gravel,  a;  2,  lower-level  gravels,  with  elephant-bones  and  flint  implements,  covered  with  river- 
loanf  twenty  to  forty  feet  thick;  3.  upper-level  gravels,  with  similar  fossils  covered  with  loam, 
in  all,  thirty  feet  thick;  4,  upland  loam,  five  to  six  feet  thick;  5,  Eocene-Tertiary. 

which  the  first  announcement  of  these  facts  was  received  have  been  en- 
tirely removed  by  careful  examination  of  the  locality  by  many  scientists, 
both  of  France  and  England. 

The  findings  were  in  undisturbed  gravels,  both  lower  (2)  and  upper 
(3),  beneath  river-loam  twenty  to  thirty  feet  thick.  Supposing  that 
the  upper  loam  (4)  represents  the  full  Champlain  flood-deposit,  then 
3  and  2  represent  the  later  Champlain  or  early  Terrace  epoch. 

In  England,  also,  at  Hoxne,  similar  flint  implements,  associated  with 
bones  of  extinct  animals,  were  found  in  strata  underlying  the  higher- 
level  river-gravels^  but  overlying  the  bowlder-drift  or  true  glacial  de- 
posit. This  fixes  the  age  as  Champlain.  Many  other  examples  of 
similar  findings  might  be  cited. 

1).  Bone-Caves — Engis  Skull. — In  the  caves  of  Belgium  and  Germany 
have  been  found  human  bones  associated  with  extinct  animals.  The 
best  example  is  that  of  the  skull  found  in  a  cave  at  Engis,  on  the  banks 
of  the  Meuse,  near  Liege.  Of  the  great  antiquity  of  this  skull  there 
seems  to  be  no  doubt.  It  was  found  in  bone  breccia,  associated  with 
bones  of  Quaternary  extinct  species  and  living  species,  beneath  a  stal- 

*  American  Journal  of  Science,  1875,  vol.  x,  p.  232. 

\  Revue  d'Anthropologie,  vol.  iii,  p.  679.  f  Nature,  vol.  xxvi,  p.  434. 

*  Nature,  vol.  xlii,  p.  508.     1890. 

39 


610 


PSYCHOZOIC  ERA— AGE  OF  MAN— RECENT  EPOCH. 


FIG.  973.— Engis  Skull,  reduced  (after  Lyell;. 


agmitic  crust.     This  association  unmistakably  indicates  the  middle  or 
latter  part  of  the  Quaternary  period. 

Neanderthal  Skull. — In  a  cave  at  Neanderthal,  near  Diisseldorf,  was 
found  a  very  remarkable  human  skeleton,  which  has  greatly  excited  the 

interest  of  scientific  men.  The 
limb-bones  are  large,  and  the  pro- 
tuberances for  muscular  attach- 
ments very  prominent ;  the  skull 
very  thick,  very  low  in  the  arch, 
and  very  prominent  in  the  brows. 
It  has  been  supposed  by  some  to  be 
an  intermediate  form  between 
man  and  the  ape ;  but,  according 
to  the  best  authority,  it  is  in  no 
respect  intermediate,  but  truly 
human.  It  is  probably  the  skel- 
eton%of  a  man  exceptionally  mus- 
cular in  body  and  low  in  intelli- 
gence. The  evidences  of  antiqui- 
ty are  of  the  same  kind,  but  less 
complete  than  in  the  case  of  the 
Engis  skull,  though  it  probably 
belongs  to  the  same  or,  perhaps, 
even  an  earlier  epoch.  The  Engis 
skull,  on  the  other  hand,  is  a  well- 
shaped  average  human  skull.  A 
figure  of  the  Engis  skull  is  given 
above  (Fig.  973),  and  a  comparison  in  outline  of  the  Neanderthal  with 
the  ape  and  European  (Fig.  974). 

Recently  there  have  been  found  in  a  cave  at  Spy,  Belgium,  two  nearly 
complete  skeletons,  which  seem  to  be  of  the  same  type  as  the  Neander- 
thal man,  and  with  the  latter  are  supposed  to  belong  to  a  distinct  and 
very  early  race.  They  are  believed  to  have  been  men  of  short  stature, 
broad-shouldered,  bowed  thighs,  slightly-bent  knees,  and  semi-erect 
posture,  but  nevertheless  distinctly  human.  The  skeletons  were  found 
associated  with  the  remains  of  all  the  characteristic  Quaternary  ani- 
mals and  implements  of  the  rudest  kind.  Their  age  was  either  Cham- 
plain  or  interglacial.* 

Mentone  Skeleton. — Several  years  ago  an  almost  perfect  skeleton 
of  a  Palaeolithic  man  was  found  in  a  cave  at  Mentone,  near  Nice.  It 
is  that  of  a  tall,  well-formed  man,  with  average  or  more  than  aver- 
age-sized skull,  and  a  facial  angle  of  85°.  The  antiquity  of  this  man 


FIG.  974.— Comparison  of  Forms  of  Skulls:  a, 
European;  b.  the  Neanderthal  man;  c,  a 
chimpanzee  (after  Lyell). 


*  Nature,  vol.  xxxv,  p.  564,  1887. 


PRIMEVAL   MAN  IN  EUROPE. 


611 


is  undoubted,  for  his  bones  are  associated  with  those  of  the  cave-lion, 
cave-bear,  rhinoceros,  reindeer,  together  with  living  species.  The  bones 
of  the  skeleton  are  all  in  place,  surrounded  with  the  implements  of  the 
chase  (flint  implements),  and  the  spoils  of  the  chase,  viz.,  the  bones  of 
reindeer,  perforated  teeth  of  stag,  etc.  Of  the  latter,  twenty-two  lay 
about  his  head.  These  are  supposed  to  have  been  worn  as  a  chaplet.  This 
Quaternary  man  seems  to  have  laid  himself  down  quietly  in  his  cave- 
home  and  died,  and  Nature  covered  his  grave  with  a  tablet  of  stalagmite. 
All  these,  and  many  more  which  might  be  mentioned,  belong  to 
the  early  Paleolithic,  although  the  last  is  probably  a  transition  to  the 
next  or  Reindeer  age.  They  were  contemporaneous  with  the  mam- 
moth, the  rhinoceros,  the  hippopotamus,  the  cave-bear,  the  cave-lion, 
the  cave-hyena,  and  other  extinct  animals ;  but  the  reindeer  had  not 
yet,  to  any  extent,  invaded  Middle  Europe  from  the  north.  They  seem 
to  have  been  savages  of  the  lowest  type,  living  by  hunting  and  dwell- 
ing in  caves,  and  their  implements  were  of  the  rudest  kind.  There  is 
no  evidence  of  agriculture  or  of  domestic  animals.  In  many  cases 
there  have  been  found  some  anatomical  characters  of  a  low  or  animal 
type,  such  as  flattened  shin-bones,  very  prominent  occipital  protuber- 
ance, less  than  usual  separation  between  the  temporal  ridges,  large 
size  of  the  wisdom  teeth,  and,  in  the  case  of  the  Neanderthal  race,  a 
very  low  arch  of  the  skull,  and  bent  knees,  etc.  But  all  these  charac- 
ters, unless  we  except  the  last  two,  are  found  now  in  some  savage  races, 
either  as  racial  or  as  individual  peculiarities. 
The  earliest  men  yet  found  are  in  no  sense 
connecting  links  between  man  and  ape.  They 
are  distinctively  human. 

Reindeer  Age  or  Later  Palaeolith- 
ic.— During  this  age  man  was 
still  associated  in  Middle 
Europe  with  Quater- 
nary animals, 
but  also  now 
with      arctic 
animals,     es- 


pecially the 
reindeer.  It 
probably  cor- 

with  broken,  burnt,  and  gnawed  bones  of  extinct  and  living  mammale,  also  ,        .., 

hearth-stones  and  works  of  art;  d,  deposit  with  similar  contents;  e,  talus  responds  Wltn 

washed  down  from  hill  above;  f  q,  slab  of  stone  which  closed  the  vault;  ,  v          m 

ft,  rabbit-burrow,  which  led  to discovery.  the       lerrace 

or      perhaps 

Second  Glacial  epoch.     The  implements  were  still  chipped,  but  much 
more  neatly. 

Aurignac  Cave. — This  sepulchral  cave  and  its  rich  contents  were 


Fio.  975.— A  Section  of  the  Aurignac  Cave:  a,  vault  in  which  remains  of  seven- 
teen human  skeletons  were  found;  6,  made  ground,  two  feet  thick,  in  which 
human  bones  and  entire  bones  of  extinct  and  living  mammals,  and  works 
of  art,  were  imbedded;  c,  layer  of  ashes  and  charcoal,  eight  inches  thick, 


612 


PSYCHOZOIC  ERA— AGE  OF  MAN— RECENT  EPOCH. 


accidentally  discovered  by  a  French  peasant.  Fig.  975  is  a  diagram 
section  of  the  cave,  taken  from  Lyell. 

On  removing  the  talus,  e,  a  slab  of  rock,/"*/,  was  exposed,  covering 
the  mouth  of  the  cave,  a.  In  this  cave  were  found  seventeen  human 
skeletons  of  both  sexes  and  of  all  sizes,  together  with  entire  bones  of 
extinct  animals  and  works  of  art.  Outside  of  the  cave  was  found  a 
deposit,  c  and  d,  consisting  of  ashes  and  cinders,  mingled  with  burnt 
and  split  and  gnawed  bones  of  recent  and  extinct  animals,  and  works 
of  art.  The  conclusion  reached  by  M.  Lartet  is,  that  this  was  a  family 
or  tribal  burial-place;  that  in  the  cave  along  with  the  bodies  were 
placed  funereal  gifts  in  the  form  of  trinkets  and  food ;  and  that  the 
funereal  feast  was  cooked  and  eaten  on  the  level  space  in  front  of  the 
cave ;  and,  finally,  that  carnivorous  beasts  gnawed  the  bones  left  on  the 
spot.  It  is  evident  that  the  Aurignac  men  practiced  religious  rites 
which  indicated  a  belief  in  immortality. 

The  following  is  a  list  of  the  animals  the  remains  of  which  were 
found  in  and  about  the  cave  ;  those  marked  f  are  either  wholly  extinct 
or  extinct  in  this  locality  : 


FAUNA  OF  AURIGNAC  CAVE. 


CAKN1VORES. 


f  Cave-bear 5  or  6 

Brown  bear 1 

Badger 1  or  2 

Polecat 1 

fCave-lion 1 

Wild-cat 1 

f  Cave-hyena 5-6 

Wolf 3 

Fox..  ..18-20 


HEBBIVOBE8. 


f  Mammoth 2  molars. 

•[Rhinoceros 1 

fHorse 12-15 

fAss 1 

Hog 1 

Stag 1 

flrishelk 1 

Roebuck 3-4 

fReindeer 10-12 

•f  Aurochs 32-15 


Perigord  Caves. — In  Southwestern  France,  along  the  course  of  the 
river  Vezere,  are  found  many  caves  in  which  are  preserved  interesting 


FIG.  976.— Drawing  of  a  Mammoth  by  Contemporaneous  Man. 


NEOLITHIC  MAN.  613 

relics  of  man  ranging  from  early  to  late  Palaeolithic.  The  Palaeolithic 
Aquitanians  seem  to  have  been  somewhat  more  advanced,  and  of  a  more 
peaceful  temper,  than  the  early  Palaeolithic  men  already  described.  Al- 
though there  is  no  evidence  of  agriculture,  they  lived  by  fishing  as  well  as 
by  hunting.  This  is  shown  by  the  number  of  fishing-hooks  of  bone  found 
there.  They  seemed  also  to  have  had  a  taste  and  some  skill  in  drawing, 
for  they  have  left  some  drawings  of  contemporaneous  but  now  extinct 
animals,  especially  the  mammoth,  the  reindeer,  and  the  horse.  Fig.  976 
is  a  piece  of  reindeer-horn  on  which  is  a  rude  etching  of  the  mammoth. 
Conclusions. — It  seems  evident  that  in  Europe  the  earliest  men  were 
contemporaneous  with  a  large  number  of  now  extinct  animals,  and  were 
a  principal  agent  in  their  extinction ;  that  they  saw  the  flooded  rivers 
of  the  Champlain  epoch,  and  the  great  glaciers  of  the  Second  Glacial 
epoch ;  but  there  is  no  reliable  evidence  yet  of  their  existence  before 
the  First  Glacial  epoch. 

Neolithic  Man  ;   Ref use- Heaps  ;  Shell- Mounds  ;  Kitchen- Middens. 

In  Northern  Europe,  especially  in  Denmark,  are  found  shell-mounds 
of  great  size,  1,000  feet  long,  200  feet  wide,  and  ten  feet  high.  They 
are  probably  the  accumulated  refuse  of  annual  tribal  feasts.  The  early 
races  of  men  in  all  countries  seem  to  have  had  the  custom  of  gathering 
in  large  numbers  at  stated  intervals,  and  feasting  on  shell-fish  and 
other  animals,  and  leaving  their  remains  in  large  heaps  to  mark  the 
spot  of  assembly.  The  evidences  of  a  very  marked  advance  are  found 
in  these  heaps.  The  implements  are  many  of  them  carefully  shaped 
or  else  polished  by  rubbing.  There  are  no  longer  any  remains  of  ex- 
tinct animals,  but  only  of  living  animals;  and  there  are  now  found 
remains  of  at  least  one  domestic  animal,  viz.,  the  dog,  though  not  yet 
any  evidence  of  agriculture.  We  have  evidence  also  at  this  time  of 
organized  communities. 

Transition  to  the  Bronze  Age— Lake-Dwellings. — In  the  Swiss, 
Austrian,  and  Hungarian  lakes  are  found  abundant  evidences  of  a  more 
advanced  race  than  any  yet  mentioned,  which  had  the  singular  custom 
of  dwelling  in  houses  constructed  on  piles  in  the  lakes,  and  connected 
with  the  land  by  mean  of  piers  or  bridges.  Similar  lake-dwellings  are 
found  now  in  New  Guinea  and  in  South  America,  and  very  recently,  by 
Lieutenant  Cameron,  in  Africa.*  By  means  of  dredging,  a  great  num- 
ber and  variety  of  implements  of  polished  stone  and  of  bronze  have 
been  obtained.  Some  of  these  ^were  evidently  used  for  ornament,  some 
for  domestic  purposes,  some  for  agriculture ;  some  were  weapons  of  war, 
some  fishing-tackle.  Many  of  these  are  wrought  with  great  skill  and 
taste.  Domestic  animals — ox,  sheep,  goat,  and  dog ;  cereal  grains — 

*  Nature,  vol.  xiii,  p.  202,  January,  1876. 


614 


PSYCHOZOIC  ERA— AGE   OF  MAN— RECENT  EPOCH. 


wheat  and  barley ;  fruits — wild  apples,  blackberry,  etc. ;  coarse  cloth, 
not  woven  but  plaited — have  also  been  found.  In  a  word,  we  have 
here  all  the  evidences  of  communities  far  above  the  state  of  savagism. 


FIG.  977.— Lake-dwellings,  restored  (after  Mortillet). 

From  this  time  the  history  of  man  may  be  traced,  by  means  of  his 
remains,  through  the  time  of  Megalithic  structures,  through  the  Eo- 
man  age,  step  by  step,  to  the  present  time.  But  this  belongs  to  the 
archaeologist,  not  the  geologist.  The  Neolithic  may  be  regarded  as 
the  beginning  of  the  Psychozoic  era — the  connecting  link  between 
geology  and  archaeology.  The  Bronze  age  and  all  that  follows  it  belong 
clearly  to  archaeology. 

Primeval  Man  in  America. 

Supposed  Pliocene  Man— Calaveras  Skull. — Several  cases  are  re- 
ported of  human  bones  and  works  of  art  having  been  found  in  the 
sub-lava  drift  described  on  page  601.  These  cases  are  none  of  them 
thoroughly  well  attested,  though  the  evidence  is  such  as  to  make  us 
suspend  our  judgment.  The  best  attested  cases  are  the  Calaveras  skull 
mentioned  by  Whitney,  and  the  Table  Mountain  skull  reported  by 
C.  F.  Winslow.  Besides  these  there  are  several  cases  reported  of  mor- 
tars and  pestles  found  in  the  sub-lava  deposit.  Many  claim  these  as 
evidence  of  the  existence  of  man  in  a  somewhat  advanced  stage  of 
progress  (at  least  as  much  so  as  the  Neolithic  man  of  Europe),  on  the 
Pacific  coast,  during  the  Pliocene  period.  The  doubts  in  regard  to 
this  extreme  antiquity  of  man  are  of  three  kinds,  viz. :  1.  Doubts  as 
to  the  Pliocene  age  of  the  gravels — they  may  be  early  Quaternary. 
2.  Doubts  as  to  the  authenticity  of  the  finds,  no  scientist  having  seen 
any  of  them  in  situ.  3.  Doubts  as  to  the  undisturbed  condition  of 
the  gravels,  for  auriferous  gravels  are  especially  liable  to  disturbance. 


PRIMEVAL   MAX   IN   AMERICA. 


615 


4 


i 


V 


*. 


« 


The  character  of  the  implements  said  to  have  been  found  gives  pe- 
culiar emphasis  to  this  last  doubt,  for  they  are  not  Palaeolithic,  but 

Neolithic. 

In  any  case,  and  whatever  be  the  geological  age  of  the  sub-lava 

drift,  if  man  should  be  undoubtedly  found  there,  it  would  show  an 
immense  antiquity;  for,  since  the  lava-flow, 
caflons  have  been  cut  by  the  present  rivers 
2,000  or  3,000  feet  deep  in  solid  slate-rock. 

Carson  Footprints. — In  1882  scientific  at- 
tention was  first  drawn  to  certain  remarkable 
tracks,  resembling  those  of  gigantic  men,  in 
the  sandstone-quarry  near  Carson,  Nevada. 
The  floor  of  the  quarry  (which  constitutes  the 
yard  of  the  State  Prison)  is  a  level  area  of 
II  Mr  about  two  acres.  The  whole  surface  of  this 

b^  6  w  area  is  covered  with  the  tracks  of  many  kinds 

of  animals.  The  depth  of  the  tracks  shows 
that  the  material  was  soft  mud  at  the  time 
the  tracks  were  made.  The  most  remarkable 
are  undoubted  tracks  of  elephants  (mammoth) 
and  especially  certain  strangely  man -like 
tracks  of  enormous  size.  These  were  eighteen 
to  twenty  inches  long  and  eight  inches  wide. 
The  stride  was  about  a  yard,  and  the  distance 

between  right  and  left  series  was  nineteen  inches. 

There  has  been  much  discussion  as  to  the  nature  of  these  tracks. 

Some  think  that  they  are  human,  and  account  for  their  great  size  by 

supposing     that     the 

men  wore  large  san- 
dals.     Others    think 
.,    that     they     are     the 

tracks     of     a     large 

ground-sloth  such   as 

the  mylodon,  which  is 

known  to  have  lived 

on   the   Pacific   coast 

in   Quaternary  times. 

Both  in  size  and  shape 

they     are      certainly' 

much  like    the    hind-    FlG'  979-~Left  kind-foot  of  Mylodon  rofcuetus,  x  }  (after  Owen). 

foot  of  the  mylodon  (Fig.  979).  But  if  made  by  a  quadruped,  the 
larger  hind-foot  must  have  obliterated  the  impression  of  the  fore-foot, 
for  there  are  apparently  but  two  series  of  tracks ;  and  the  feet  must 
have  been  clogged  with  mud,  for  no  impression  of  toes  is  seen.  It  is 


Fio.  978.— Two  Series  of  Tracks 
in  Carson  Prison-yard. 


616 


PSYCHOZOIC  ERA— AGE  OF  MAN— RECENT  EPOCH. 


significant,  however,  that  the  elephant-tracks,  also,  formed  but  two 
series. 

The  weight  of  evidence  is  probably  in  favor  of  the  mylodon,  but 
in  any  case  there  seems  no  reason  to  believe  the  age  of  the  strata  to  be 
earlier  than  the  Quaternary.  The  only  reason  for  assigning  them  to 
an  earlier  period  (Pliocene)  is  their  lithified  condition.  But  the  pres- 
ence in  the  quarry  of  hot  springs,  containing  abundance  of  lime-carbon- 
ate, sufficiently  accounts  for  this. 

Quaternary  Man. — Leaving  out  all  doubtful  cases,  the  first  appear- 
ance of  man  in  America  seems  to  have  been  about  the  same  time  as 
or,  perhaps,  a  little  later  than  in  Europe.  On  the  Pacific  coast  his 
implements  are  found  in  great  abundance  in  river-gravels,  associated 
with  remains  of  the  mammoth,  the  great  mastodon,  and  the  horse. 
On  the  Eastern  part  of  the  continent,  also,  the  existence  of  man  before 
the  ice-sheet  had  disappeared  from  the  United  States,  is  distinctly 
proved.  One  of  the  best  examples  of  this  is  found  in  the  discovery  by 
Miss  Babbitt,  at  Little  Falls,  Minnesota,  of  rude  flint  implements  in 
deposits,  which  were  formed  during  the  final  retreat  of  the  ice-sheet 
from  that  region.*  Another  good  example,  is  the  discovery  by  Abbott, 
in  gravels  near  Trenton,  New  Jersey,  of  rude  flint  implements,  similar 
to  Palaeolithic  implements  everywhere.  The  gravels  are  acknowledged 
to  have  been  formed  during  the  retreat  of  the  ice-sheet  from  New  Jer- 
sey. We  give  here  a  figure  of  one  of  these  flints  (Fig.  980).  Still 

more  recently  hu- 
man implements 
have  been  found 
in  Ohio,  under 
conditions  which 
prove  that  man 
lived  there  while 
the  northern  part 
of  the  Mississippi 
Valley  was  still  ice- 
sheeted  (Wright). 

There  seems  to 
be  no  doubt,  there- 
fore, that  in  Amer- 
ica, as  in  Europe, 
man  saw  the  retreating  ice-sheet  and  the  flooded  lakes  and  rivers  of 
the  Champlain  times. 

The  history  of  the  American  man  can  be  traced  onward  in  refuse- 


FIG.  980.— Palaeolith  found  by  Abbott  in  New  Jersey,  slightly  reduced 
(after  Wright). 


*  American  Naturalist,  vol.  xviii,  pp.  594,  697,  1884;  and  Wright's  Ice  Age,  p.  538 
et  seq. 


PRIMEVAL  MAN  IN  AMERICA.  617 

heaps  and  shell-mounds  ;  in  the  great  mounds  of  the  so-called  mound- 
builders,  scattered  over  the  whole  Eastern  part  of  the  continent,  but  es- 
pecially abundant  in  the  valley  of  the  Mississippi ;  and,  finally,  in  the 
wonderful  cliff-dwellings  and  buried  cities  of  New  Mexico  and  Arizona. 
But  all  this,  though  of  extreme  interest,  belongs  to  archaeology  rather 
than  geology. 

Quaternary  Man  in  Other  Countries. — In  India*  Palaeolithic  imple- 
ments, precisely  like  those  found  in  Europe,  and  elsewhere,  were  found, 
in  1873,  associated  with  extinct  species  of  elephant,  hippopotamus, 
rhinoceros,  and  bear,  in  Quaternary  deposits.  In  the  South  American 
bone-caverns  human  remains  have  been  found  associated  with  Quater- 
nary animals. 

Man,  therefore,  has  been  traced  back  with  certainty  to  the  Cham- 
plain  and  even  to  the  interglacial  epoch.  It  is  possible  that  he  may  be 
hereafter  traced  farther  to  the  Glacial  or  pre-Glacial  period.  Some 
confidently  expect  that  he  will  be  traced  to  the  Miocene,  but  this  seems 
extremely  improbable,  for  the  following  reasons : 

a.  He  has  been  diligently  searched  /or,  without  success.    Now, 
while  negative  evidence  is  rightly  regarded  as  of  little  value  in  geol- 
ogy, yet,  in  this  instance,  it  is  undoubtedly  of  far  more  than  usual 
value,  because  man's  works  are  far  more  numerous  and  far  more  im- 
perishable than  his  bones. 

b.  Man  probably  came  in  with  the  present  mammalian  fauna.    We 
repeat  here  the  diagram  illustrating  the  law  of  extinction  and  appear- 

T     I      A     R       Y         I  QUATERNARY     lRCC£NT~ 


Ltft  f/iuiuub  r 

EOCENE 

|  MIOCENE 

|  PLIOCENE: 

\1&LAC 

CHAM 

TER 

RECENT 

Fio.  881. 

ance  of  species.  It  is  seen  that  lower  species  are  far  less  rapidly 
changed  than  higher.  Living  foraminifers  may  be  traced  back  into 
the  Cretaceous ;  living  shells  and  other  invertebrates  to  the  beginning 
of  the  Tertiary :  but  living  mammals  pass  out  rapidly  and  disappear 
in  the  Middle  Quaternary.  Not  a  single  species  of  mammal  now  living 
is  found  in  the  Tertiary.  Shall  man,  the  highest  of  all,  be  the  only 
exception  ?  Man  is  one  of  the  present  mammalian  fauna,  and  came  in 
with  it. 

But,  again,  several  distinct  mammalian  faunas  have  appeared  and 

*  American  Journal  of  Science,  1875,  vol.  x,  p.  232. 


618 


PSYCHOZOIC  ERA— AGE  OF  MAN— RECENT  EPOCH. 


FIG.  982.— Diagram  illustrating  the  Appearance  and  Extinction 
of  Successive  Mammalian  Faunae. 


disappeared  since  the  beginning  of  the  Miocene.  The  Miocene  mam- 
malian fauna  is  totally  different  from  the  Eocene ;  the  Pliocene  totally 
different  from  the  Miocene ;  the  Quaternary  from  the  Pliocene ;  and 
the  present  from  the  Quaternary.  This  is  graphically  represented  in 
the  diagram,  Fig.  982,  in  which  the  alternate  shaded  and  white  spaces 
•  , ,  represent  five  con- 

secutive mammalian 
faunas  (there  are 
really  many  more 
than  five)  overlap- 
ping each  other,  but 
substantially  distinct. 
It  seems  in  the  high- 
est degree  improbable  that  man,  a  mammal,  should  survive  the  appear- 
ance and  disappearance  of  several  mammalian  faunas. 

Or,  again,  to  put  it  still  another  way :  We  have  seen  (p.  537,  Fig. 
917)  that,  speaking  generally,  existing  mammalian  species  commenced 
to  be  introduced  in  the  Quaternary ;  existing  genera  in  the  Pliocene ; 
and  existing  families  in  the  Miocene.  If,  therefore,  a  tool-making 
animal  should  be  found  in  the  Miocene,  as  some  believe,  it  might  be  of 
the  family  of  Hominidce,  but  not  the  genus  homo.  If  such  should  be 
found  in  the  Pliocene,  it  might  be  of  the  genus  homo,  but  not  the  spe- 
cies sapiens.  Even  the  earliest  Quaternary  man — the  so-called  Nean- 
derthal race — is  supposed  by  Mortillet  to  have  been  a  different  species 
from  existing  man. 

Time  since  Man  appeared. — Geology  reckons  her  time  in  periods, 
epochs,  etc. ;  History  hers  in  years.  It  is  impossible  to  express  the 
one  chronology  in  terms  of  the  other  except  in  a  very  rough  approxi- 
mative way,  for  want  of  a  reliable  common  measure.  If  Mr.  CrolPs 
theory  of  glacial  cold  should  indeed  prove  true,  then  we  might  hope  to 
measure  man's  time  on  the  earth  with  some  degree  of  accuracy.  But 
in  the  absence  of  confidence  in  this  theory,  our  only  resource  is  to  use 
the  measure  which  we  have  already  used  on  several  occasions,  viz.,  the 
effects  of  causes  now  in  operation.  This  measure,  however,  can  give 
but  very  rough  approximate  results. 

There  is  no  doubt  that  very  great  changes,  both  in  physical  geog- 
raphy and  in  the  mammalian  fauna,  have  taken  place  since  man  ap- 
peared. Judging  by  the  rate  of  changes  still  in  progress,  we  are  natu- 
rally led  to  a  conviction  of  a  lapse  of  time  very  great  in  comparison 
with  that  recorded  in  history  On  the  other  hand,  some  attempts  to 
estimate  more  accurately  by  means  of  the  growth  of  deltas  in  which 
have  been  found  implements  of  the  Eoman  age,  the  Bronze  age,  and 
the  Stone  age ;  and  by  the  progressive  erosion  of  lake-shores  and  the 
recession  of  waterfalls,  which  is  supposed  to  have  commenced  after 


CHARACTER   OF   PRIMEVAL   MAN.  619 

the  Ghamplain  epoch,  have  led  to  very  moderate  results,  viz.,  7,000  to 
10,000  years.  While  these  results  can  not  be  received  with  any  confi- 
dence, yet  it  is  hoped  that  many  such  will  continue  to  be  made. 

In  conclusion,  we  may  say  that  we  have  as  yet  no  certain  knowledge 
of  man's  time  on  the  earth,  unless  we  adopt  C roll's  theory  of  the  Gla- 
cial climate.  It  may  be  100,000  years,  or  it  may  be  only  10,000  years. 

II. — CHARACTER  OF  PRIMEVAL  MAN. 

In  regard  to  the  second  question,  viz.,  the  character  of  primeval 
man,  we  will  make  but  one  remark.  We  have  seen  that  the  earliest 
men  yet  discovered  in  Europe  or  America,  though  low  in  the  scale  of 
civilization,  were  distinctively  human,  and  not  in  any  sense  an  inter- 
mediate link  between  man  and  the  ape.  Nevertheless,  we  must  not 
forget  that  the  cradle  of  mankind  was  probably  in  Asia.  Man  came  to 
Europe  and  America  by  migration.  The  intermediate  link,  if  there 
be  any  such,  must  be  looked  for  in  Asia.  This  question  can  only  be 
settled  by  a  complete  knowledge  of  the  Quaternary  of  that  country. 

In  any  case,  man  is  the  ruler  only  of  the  modern  era.  The  presence 
of  man  in  Quaternary  times  must  be  regarded  as  an  example  under  the 
law  of  anticipation  (p.  280).  He  only  fairly  established  his  supremacy 
in  the  Recent  epoch,  and  therefore  the  age  of  man  and  the  Psychozoic 
era  ought  to  date  from  that  time. 


LIST  OF  THE 

PRINCIPAL  AUTHORITIES  FOR  THE  ILLUSTRATIONS  IN  THIS  WORK, 
AND  THE  BOOKS  FROM  WHICH  THEY  HAVE  BEEN  TAKEN. 


AGASSIZ,  L.     Etudes  sur  les  Glaciers ;  Poissons  Fossiles. 

ASHBURNER,  CHARLES  A.     Anthracite  Fields  of  Pa. 

AUTHOR.  American  Journal  of  Science,  III,  1872-'89;  also  many  (about 
150)  diagrammatic  illustrations  throughout  this  work. 

BAILEY,  J.  W.     Am.  Jour,  of  ScL,  II,  i. 

BEECHER.     Am.  Jour,  of  Sci.,  1889. 

BRADLEY,  F.  H.     Geological  Chart  of  the  U.  S. 

BROGNIART,  A.     Histoire  des  Vegetaux  Fossiles. 

BUCKLAND,  W.     Bridgewater  Treatise. 

CHAMBERLIN,  T.  C.     Kettle  Moraine.     Trans.  Wis.  Acad.  Sci.,  1879. 

CONRAD,  T.  A.     Jour.  Acad.  Sci.,  Philadelphia. 

COPE,  E.  D.  Hayden's  U.  S.  Geog.  and  Geol.  Survey,  vol.  ii — Cretaceous 
Vertebrates;  Newberry's  Ohio  Survey  Pal. — Reptiles  of  the  Coal;  Proc.  Am. 
Phil.  Soc.,  vols.  xvii  and  xix — Permian  and  Jurassic  Reptiles;  Origin  of  the 
Fittest. 

DADDOW,  S.  H.     Coal,  Iron,  and  Oil. 

DANA,  J.  D.  Wilkes's  U.  S.  Explor.  Exped. — vol.  on  Gfeology ;  Manual  of 
Geology. 

DAVIS,  W.  M.     Trias  of  Conn.  River.     Am.  Jour,  of  Sci.,  1889. 

DAWSON,  J.  W.     Acadian  Geology. 

DE  LA  BECHE,  H.  Geological  Observer — Sections  and  Views  of  Geological 
Phenomena. 

DE  LA  NOE  and  DE  MARGERIE.     Les  Formes  du  Terrain. 

DE  MARGERIE  and  HEIM.     Dislocation  de  1'Ecorce  Terrestre. 

D'ORBIGNY,  A.     Paleontologie  et  Geologic. 

EMMONS,  E.     Rep.  Geol.  of  N.  Y. ;  Rep.  Geol.  of  N".  C. 

EWING.     Seismograph. 

FAVRE,  Prof.  ALPH.     Archives  des  Sciences,  vol.  Ixii. 

FONTAINE,  W.  M.  Flora  of  Potomac  Formation,  U.  S.  Geol.  Survey.  Mono- 
graph. 

FORBES,  J.     Alps  of  Savoy. 

FOSTER  and  WHITNEY.     Rep.  on  Geology  of  L.  Superior  District. 

FRITSCH.     Permian  Fauna. 


LIST  OF  AUTHORITIES.  621 

GABB,  W.  M.     Whitney's  Geol.  Survey  of  California. 

GAUDRY,  A.     Monde  Animale. 

GEIKIE,  A.     Text-Book  of  Geology. 

GEIKIE,  J.     Great  Ice  Age. 

GILBERT,  G.  K.     Geology  of  the  Henry  Mountains. 

GRATACAP.     Concretions  or  Nodules.     Am.  Nat.,  1884. 

GiiNTHER,  A.     Trans.  Roy.  Soc.,  1871. 

GUYOT,  A.     Physical  Geography. 

HALL,  J.  Rep.  Paleontology  of  N.  Y. ;  Rep.  Geol.  of  Iowa;  Rep.  on  State 
Cabinet  of  N.  Y. 

HAYDEN,  F.  V.     Rep.  Geog.  and  Geol.  Survey  of  Territories,  1871-73. 

HEER,  Prof.     Primeval  World  of  Switzerland. 

HILGARD,  E.  W.     Rep.  Agric.  and  Geol.  of  Miss.,  1860. 

HITCIICOCK,  C.  H.     Geol.  Map  of  U.  8. 

HITCHCOCK,  E.     Ichnology  of  Mass.,  1858. 

HOLMES,  W.  H.     Drawing  of  Geyser  Eruption. 

HOWELL,  E.  E.     U.  8.  Geog.  Survey  by  Wheeler,  vol.  iii— Geology. 

JUKES  and  GEIKIE.     Manual  of  Geology. 

HUXLEY,  T.  H.  Manual  of  Anat.  of  Vertebrates;  Anat.  of  Invertebrates; 
Rhynchosaurs.  Quar.  Jour.  Geol.  Soc.,  1887. 

JACKSON,  W.  H.     Photograph  of  Geyser  Eruption. 

JOHNSTONS,  A.  K.     Phys.  Atlas,  last  edition. 

KINO,  CLARENCE.     Geol.  Survey  of  40th  Parallel,  vol.  i. 

LEIDY,  J.  Cretaceous  Reptiles  of  U.  8. ;  Smithsonian  Contributions,  1865 ; 
Fossil  Vertebrates  of  U.  8. ;  Hayden's  Geol.  Survey  of  Terr.,  vol.  i. 

LESLEY,  J.  P.     Manual  of  Coal  and  its  Topography. 

LESQUEREUX,  L.  Owen's  Rep.  Geol.  of  Ky. ;  Owen's  Rep.  Geol.  Ark. ; 
Hayden's  Geog.  and  £eol.  Survey,  vol.  vi ;  Cret.  Flora  of  U.  8. 

LOGAN,  W.     Rep.  Geol.  Canada. 

LYELL,  C.     Principles  of  Geology ;  Elements  of  Geology ;  Antiquity  of  Man. 

MALLET,  F.  R.     Barren  Island.     Geol.  Survey  of  India. 

MANTELL,  G.  A.     Fossils  of  British  Museum. 

MAOUT  and  DECAISNE.     General  System  of  Botany. 

MARSH,  O.  C.  Jurassic  and  Cretaceous  Reptiles  and  Birds,  and  Jurassic 
and  Tertiary  Mammals;  Am.  Jour,  of  Sci.,  1871-'90. 

MEEK  and  WORTHEN.     Geol.  Survey  of  111.,  vols.  ii,  iii,  iv,  v,  vi. 

MEEK,  F.  B.  Whitney's  Geol.  Survey  of  California,  vol.  i;  Newberry's 
Geol.  Survey  of  Ohio  Pal.,  vols.  i  and  ii;  Palaeontology  of  Upper  Missouri; 
Smithsonian  Contributions,  1864. 

MURCHISON,  R.  I.     Siluria. 

NEWBERRY,  J.  8.  Rep.  Geol.  Survey  of  Ohio;  Geol.  of  Macomb  Expedi- 
tion ;  Pacific  R.  R.  Reports,  vol.  vi. 

NICHOLSON,  H.  A.  Manual  of  Palaeontology ;  Manual  of  Zoology ;  Ancient 
Life  History. 

OSBORN,  H.  F.  Mesozoic  Mammals;  Jour.  Acad.  Nat.  Sci.,  Philadelphia, 
1888;  Mammalia  of  Uintah  Formation.  Mem.  Am.  Phil.  Soc.,  1889. 

OWEN,  D.  D.     Rep.  Geol.  of  Wisconsin,  Iowa,  etc. 

OWEN,  R.  British  Fossil  Mammals ;  Palaeontology ;  Trias  Reptiles ;  Quar. 
Jour.  Geol.  Soc.,  1887. 


622  LIST  OF  AUTHORITIES. 

PACKARD,  A.  S.  Life-Histories;  Manual  of  Zoology;  Syncarida.  Mem. 
Jour.  Nat.  Acad.  Sci. 

PHILLIPS,  J.     Manual  of  Geology ;  Geology  of  Oxford. 

PICTET,  F.  J.     Traite  de  Paleontologie. 

POWELL,  J.  W.  Exploration  of  Colorado  River ;  Geology  of  Uintah  Mount- 
ains. 

PRESTWICH.     Geology. 

ROGERS,  H.  D.     Rep.  Geol.  of  Pennsylvania. 

RUSSELL,  I.  C.  Lake  Lahontan;  Southeastern  Oregon.  U.  8.  G.  8.  Mon- 
ograph, 11.  Annual  Report,  1884. 

SAFFORD,  J.  M.     Rep.  Geol.  of  Tennessee. 

SEELEY,  H.  G.     Geol.  Mag.,  vol.  viii,  1881. 

SCUDDER,  S.  H.  Worthen's  Rep.  Geol.  of  111.,  vol.  iii.  Eighth  Annual 
Report  U.  S.  G.  S. 

SEKIYA,  S.     Seism.  Soc.  of  Japan,  vol.  xi. 

SHARPE,  D.     Quar.  Jour.  Geol.  Soc.,  vol.  iii,  1847. 

SORBY,  H.  C.     Philosophical  Magazine,  2d  series,  vol.  xi. 

STEVENSON,  J.  J.     Wheeler's  U.  S.  Geol.  Survey,  vol.  iii — Geology. 

TAYLOR,  R.  C.     Statistics  of  Coal. 

TRAQUAIR.     Devonian  Fishes.     Ann.  and  Mag.  Nat.  Hist.,  1890. 

TYNDALL,  J.     Glaciers  of  the  Alps. 

UPHAM,  WARREN.     Ice  Sheet  Moraine;  Geol.  Survey  of  Minn.,  1880.    - 

WAILES,  B.  L.  C.     Rep.  Agric.  and  Geol.  of  Miss.,  1854. 

WALCOTT,  C.  D.     Rep.  N.  Y.  Cabinet  of  Nat.  Hist.,  1877. 

WALLACE,  A.  R.     Geographical  Distribution  of  Animals ;  Island  Life. 

WARD,  H.     Illustrated  Catalogue  of  Casts. 

WARD,  LESTER  F.     Laramie  Flora;  U.  8.  G.  S.  Bulletin,  37. 

WHEELER,  G.  M.     U.  S.  Geog.  Survey  west  of  100th' Meridian. 

WHITE,  C.  A.  Wheeler's  Survey,  vol.  iv— Palaeontology.  U.  S.  G.  S.  An- 
nual Report. 

WHITNEY,  J.  D.  Geol.  Survey  of  California ;  Geol.  of  L.  Superior  District ; 
Auriferous  Gravels  of  California. 

WOODWARD,  S.  P.     Manual  of  Mollusca. 

WORTHEN.     Geol.  Survey  of  Illinois. 

ZITTELL.     Trait6  de  Paleontologie. 


INDEX 


Abbot H6 

Acanthotelson  Stimpsoni 896 

Acanthoteuthis  antiquus 488 

Acephals,  or  Bivalves 813 

Acer  trilobatum 509 

Acervularia  Davidsoni 381 

Acid,  humus 4 

Acidaspis  crosotus 823 

Acrodua  minimus 418 

—  nobilis 486 

Acrogens,  age  of 282,  845 

Actinoceras 818 

^Epiornis 605 

JSschna  eximia 435 

Agassiz,  A 134,  160 

Louis 157,  481 

Lake 556 

Agencies,  aqueous 9 

—  atmospheric 8 

igneous 88 

organic 140 

Age  of  acrogens  and  amphibians 345 

fishes. 827 

invertebrates 296 

mammals 501 

man 608 

reptiles 414 

Ages 282 

Agnostus  interetrictus 299 

Aitkin 68 

Alecto  auloporoidcs 810 

Alethopteris  lonchitica 364 

Massilonis 363 

Whitneyi 459 

Alkaline  lakes 79 

Allorisma  pleuropistha 395 

ventriccsa 395 

Alnus  grewiopsis 497 

Alps 260 

AmblypteniB  macroptenia 399 

Ambonychia  bellistriata 316 

American  mud-fish 338 

Amia 338 

Ammonites  bifrons 431 

cordatus 431 

Chicoensis  ...  . .  482 


PACK 

Ammonites  Humphreysianns 430 

Jason 431 

Jurassic 430 

—  margaritanus 431 

Ammophila  inferna 514 

Amphibians,  age  of 282,  345 

carboniferous 400 

Amphitherium 448 

—  Prevostii 448 

Amygdaloid 215 

Amygdules 215 

Anchithere 541 

Ancyloceras  pcrcostatus 482 

Andesite 208 

Andrias  Scheuchzeri 520 

Japouica 520 

Andromeda  vaccinifoliee  aifinis 508 

Angiosperms 474 

Animals,  Carboniferous 390 

Cretaceous 477 

Devonian 382 

Jurassic 428 

—  J  ura-Trias 453 

Permian 411 

Quaternary 575 

Silurian 304 

Tertiary 511 

—  Triassic 416 

Annelids,  Silurian 321 

Annularia  inflata 371 

Anomalocardia  Mississippiensis 512 

Anomodonts 419 

Anomoepus  minor 456 

Anoplotherium  commune,  restored 524 

Anoura 400 

Anthophyllitis  Devonicus 331 

Anthracite 354 

—  region  of  Pennsylvania,  map 349 

section,  magnified 352 

Anthracopupa  Ohioensis 394 

Anthracosaurus 403 

Anthrapaltemon  gracilis 396 

Anthrobycosa-antiqua 897 

Anticline 178 

Antiquity  of  man 607,  618 

Apateon 403 

Apatorni* 489 


624: 


INDEX. 


PAGE 

Apiocrinus  Roissiantis 429 

Apis  Adamitica 514 

Aporrhais  f  alcif  ormis 481 

Appalachian  chain 258 

—  coal-field 375 

—  revolution 377,  409 

Apteryx  Australia 606 

Aptornis  didif ormis 604 

Aqueous  agencies 9 

Aqueo-igneous  fusion 91 

Aralia  digitata 496 

Araliaephyllum  obtusifolium 476 

Araucaria,  cone 427 

Araucariae : 361 

Araucarites  gracilis 359 

Archaean  or  Eozoic  age 285 

and  Palaeozoic  eras,  interval  between . . .  294 

era,  time  represented 288 

—  times,  physical  geography 287 

evidences  of  life 288 

Archaaocidaris  Wortheni 393 

Archaeopteryx  macroura 445 

Berlin  specimen 445 

Archegosaurus 402 

Archimedes  Wortheni 391 

Areuicolites  didymus 300 

Armadillos 587 

Armstrong 351 

Artesian  wells ' 75 

Arthrophycus  Harlani 303 

Articulates 320 

Artiodactyls 539 

Asaphus  gigas 324 

Aspidura  loricata   416 

Astarte  excavata 429 

Astartella  Newberryi 395 

Asteria  lombricalis. 429 

Asteroids,  Silurian 310 

Asterophyllites  foliosus 371 

latifolia 330 

Atlantic  Ocean,  currents  of 41 

Atlantochelys  gigas 486 

Atlantosaur  beds 460 

Atlantosaurus  immanis 461 

Atmosphere,  mechanical  agencies  of 8 

Atmospheric  agencies 3 

Atolls 148 

small - 149 

Aucella  Erringtonii 479 

Augite 204 

Auriferous  quartz  veins 240 

Aurignac  Cave 611 

Avicula  contorta 417 

socialis 417 

Trentonensis d!6 

Aviculopecten  parilis 333 

Axes,  anticlinal 178 

synclinal 178 

B 

Babbage's  theory  of  movements  of  the  earth's 

crust 138 

Bache...  ..  126 


PAGE 

Baculites  anceps 482 

Bad  Lands 268,  504 

Lands,  Miocene  mammals 535 

Baieropsis  foliosa 476 

Bakewellia  parva 411 

Balanced  stones 57 

Banks,  submarine 43 

Baphetes * . .  403 

Baptanodon  discus 466 

Barraude 324 

Barren  Island,  section 96 

Bars 32 

Basalt 208 

columnar  structure 212 

Base-level  of  rivers 21 

Basin,  hydrographical 10 

Bat,  fore-limb. 447 

Batocrinus  Chrystii 392 

Beaches  and  terraces 579 

Becker 246,  248 

Belemnites 432 

clavatus 433 

densus 458 

fossil  ink-bags 433 

hastatus 433 

—  impressus 481 

Owenii 433 

unicanaliculatus 433 

Bellerophon  Newberryi 333 

sublaevis 395 

Belodon 520 

Beryx  Lewesiensis 484 

Big  Bone  Lick 582 

Bird,  fore-limb 447 

Birds,  Cretaceous 488 

\ —  Jurassic. : 444 

origin 448 

Tertiary £  20 

gigantic  extinct,  of  New  Zealand 605 

toothed 48 

Bischof 79,  82,  240,  385,  422 

Bitumen,  geological  relations 386 

origin 389 

Bituminous  coal 354 

Blandf  ord 96 

Blastids,  Carboniferous 391 

Blatta  Helvetica 397 

Blattina  f ormosa 435 

Bog-iron  ore 143 

Bombus  jurinei 514 

Bone-caverns 577,  582,  609 

origin 578 

Bone-rubbish,  cave,  origin 578 

Bores 32 

Bos  primigenius. 606 

Bowlders 548 

of  disintegration 6 

Brachiopods,  general  description .314 

Carboniferous 394 

Cretaceous 478 

Devonian 332 

Jurassic 428 

Silurian 313 

Brachiospongia  Rcemerana 305 


r 


IXDEX. 


625 


PAGE 

Brachyphyllum 459 

Brains  of  coryphodon,  dinoceraa,  and  bron- 

totherium  compared 538 

Bnunathere 526 

Branner 32 

Breccia 214 

Brid^er  beds 688 

Brogniart 398 

Brontops  restored 463 

Brontosaurus 463 

excelsis .' 462 

Brontotheridte 535 

Brontothcriiim,  skull  and  brain. 688 

Bronto/oum  giganteum 455 

Bronze  age 607 

—  transition  to 613 

Bmwen 107,  109,  110 

Buprcstidium 435 

Buthotrephis  gracilis 303 

—  succulens 303 

Buttes 17 

Buttes  of  the  Cross  . .  .16 


Calamite,  restoration 372 

Catamites  and  their  allies 871 

cannaef  ormis 871 

Calaveras  skull 614 

Calc-spar 235 

California  Miocene  shells 618 

Callipteris  Sullivanti 863 

Calymene  Blumcnbuchii 322 

senaria 822 

Camarasaurus 461 

Cambrian  system 296 ' 

Camptosaurus  dispar 464 

Cancellaria  vetusta 513 

Canon,  Grand 17 

Canons,  how  formed 15  j 

Cape  May 86 

Caprina  adverea 480 

Carboniferous  age 845 

animals 890 

bivalve  and  univalve  shells 392 

—  brachiopods 894 

conifers',  affinities 861 

corals 391 

crustaceans 896 

echinoderms 892 

fishes 398 

fresh-water  shells 892 

goniatites 895 

insects 397 

—  period  proper,  estimate  of  time 377 

period  proper,  rock-system 346 

plants,  structure  and  affinities 858 

system  and  age,  subdivisions 845 

vertebrates 398 

Carcharodon  augustidens 518 

-megalodon 618 

Carcinas  moenas,  development 435 

Cardiocarpon 360 

Cardiocarpum  Baileyi 831 

40 


PAGE 

Cardiola  interrnpta 316 

Cardium  Hillanum 184 

—  Meekianum 513 

—  Kha'ticum • 417 

Carpolitnes  irregularis 508 

Carson  footprints 615 

Caryocrinus  ornatus 312 

Casts  of  organic  remains 194 

Caruthers 362 

Catskill  period 828 

Caulopteris  primeva 865 

Cave  bear 577 

Gailenreuth 576 

—  hyena 577 

Caves,  limestone 76 

Cenozoic  era 501 

divisions 501 

—  general  characteristics 501 

Cephalaspis  Lyelli 336 

Cephalopods,  Carboniferous 892 

Cretaceous 480 

Devonian 333 

—  diagram  showing  distribution  in  time.. .  434 

—  Jurassic 428 

—  Silurian 317 

—  enture  and  siphon 431 

Ceratites,  nodosus 417 

Whitneyi 460 

CeratoduB 839 

—  altus,  dental  plate 418 

—  Foeterii 838 

—  Berratus,  dental  plate 418 

—  structure  of  limbs 841 

Cervus  Americanus 582 

megaceroe,  skeleton 579 

Ceatracion  Phillippi 338 

Ceteosaur 441 

Chalk 470 

cliffs 191 

—  continuity 492 

—  foraminifera  of 471 

—  origin 472 

—  seas  of  cretaceous  times,  extent  in  Eu- 
rope    478 

—  seen  under  the  microscope 471 

Chalybeate  waters 79 

Chamserops  Ilelvetica 509 

Chamberlio 246 

Champlain  in  Europe 572 

epoch 545,  555 

Chance 846 

Cheirotherinm 420 

Chemical  effects  of  subterranean  waters 76 

Chemnng  period 828 

Chlamydotherium 587 

Chlorite-schist 220 

Choke-damp 356 

Chonetes  Dalmaniana 894 

Chronology,  geological,  manner  of  construct- 
ing   199 

Chrysalidina  gradata 471 

Church  of  Recnlvere 87 

Cimolomys  gracilis 500 

Cinder-cone,  section 94 


G26 


INDEX. 


PAGE 

Cinnamomum  Mississippiense 508 

polymorphum 509 

Circulation,  illustrations  of  law 249 

Cladodus  spinosus 399 

Clay  formation 7 

slate 220 

Claypole  254 

Cleavage,  association  with  contorted  laminae.  184 

association  with  foldings  of  strata 184 

crystalline 182 

flag-stone 182 

organic 182 

—  physical  theory  of • 185 

planes 182 

—  slaty,  Sharpe's  theory 183 

Sorby's  theory 185 

structure 181 

theory,  geological  application. . . .'. 187 

Tyndairs  theory 186 

Clinometer 177 

Clisiophyllum  Gabbi 391 

Club-moss  compared  with  lepidodendron 367 

Clupea  alta 518 

Clypeus  Plotii 429 

Coal  areas  of  different  countries  compared. .  351 
areas  of  the  United  States 350 

calamites 370 

— -  conifers 358 

Cretaceous 473,  498 

estuary  or  raft  theory 373 

extra-carboniferous 351 

fat  or  fusing 354 

ferns 362 

field,  Appalachian 375,  377 

field,  central 376 

field,  Richmond  and  North  Carolina 456 

field,  Western 376 

formation,  estimate  of  time 377 

formation  of 350 

Jura-Trias 456 

Jura-Trias,  fossils  457 

lepidodendrids *. 365 

measures,  iron-ore 383 

measures,  Jurassic 425 

measures,  plication  and  denudation 348 

measures,  thickness  of  strata 346 

metamorphic 356 

modes  of  occurrence 346 

origin; '. 352 

peat-bog  theory 373 

period,  climate 379 

period,  physical  geography 378 

plants,  fruits 360 

plants,  general  conclusions 372 

plants,  living  congeners 359 

—  plants,  principal  orders 358 

plants,  where  found • 358 

—  relative  production 351 

—  seams,  faults 349 

seams,  number  and  thickness. 349 

sigillarids 368 

—  steam 354 

—  theory  of  accumulation 373 

varieties . .  353 


PAGE 

Coal,  varieties,  origin 354 

vegetable  structure  in 353 

—  water  present  during  accumulation 373 

Coast  Range  of  California 259 

Range,  time  of  formation 544 

Coccoliths 471 

Coccospheres 471 

Coccosteus 339 

—  decipiens 336 

Cochliodus  contortus 399 

Coelurus  f ragilis 460 

Colorado  canon 16 

Colossochelys  Atlas 520 

Columbia  River  falls 14 

Columnaria  alveolata 306 

Columnar  structure  of  rocks 212 

Columns,  granitic 227 

Comanche  group 473 

Comatula  rosacea 311 

Compsognathus 442 

Concretions,  limestone 190 

Conformable  strata 179 

Conglomerate,  true 171 

volcanic 214 

Conifer,  trunk  of  Carboniferous 358 

Coniferous  wood,  fossil  and  recent 328 

Conifers  of  Jura-Trias 459 

—  Triassic 415 

Coniopteris  Murrayana 427 

Connecticut  River  sandstone 452 

Conocardium  trigonale 333 

Continental  form,  laws  . . . ; 169 

Conularia  Trentonensis 317 

Cope  ....  404,  413,  449,  460,  461,  486,  487,  488,  494 

Copper- veins 239 

Coral,  compound,  or  corallum 145 

forests 145 

growth,  conditions  of 147 

islands 146 

islands,  amount  of  vertical  subsidence. .  153 

islands,  area  of  land  lost 153 

islands,  crater  theory 150 

-, —  islands,  Murray's  theory 152 

islands,  rate  of  subsidence 154 

islands,  subsidence,  geological  applica- 
tion   155 

islands,  subsidence,  theory  of .•  150 

islands,  subsidence,  time  involved 155 

polyp 145 


reefs 146,  147 

reefs,  barrier  and  circular,  theories 150 

reefs,  Darwin's  theory 150 

reefs,  Murray's  theory 152 

reefs,  Florida 156' 

reefs,  Pacific 147 

Corals.  Carboniferous 391 

..  304 


cup 


304 


cyathophylloid 

Devonian 332 

—  Favositid 304 

Halysitid 304 

Jurassic , 428 

Silurian 304 

Corbicula  f  racta 498 


INDEX. 


627 


PAGE 

Cordaites 861 

—  Robbii 331 

Corniferoue  period 328 

Cornulites  serpentarius 

Corydaloides  Scudderi  . .   397 

Coryphodon  beds 530 

—  hamatus 531 

—  skull  and  bruin 538 

Cretaceous 469 

—  animals 477 

—  birds 488 

—  coal 473,  498 

—  echinoderms 478 

—  fishes 482 

—  ma  in  nulls    492 

—  mollusks 478 

—  period,  physical  geography  in  America.  469 

—  plants 474 

—  reptiles 484 

-  rocks 470 

—  rocks,  area  in  America 469 

—  sponges 477 

—  subdivisions 478 

Crinoids,  Carboniferous 891 

—  distribution  in  time 893 

—  Jurassic 428 

—  living 810 

—  Silurian 810 

—  Triassic 416 

Crioceras 482 

Cristellaria  subart natula 472 

Critical  periods 410,  594 

Crocodilians 439 

Croll . .  89,  65 


Croll's  theory  of  glacial  climate 590 

Crossopterygians 839 

Crust  of  the  earth,  elevation  and  depression.  133 

Crustaceans,  Carboniferous . .  393 

Devonian 333 

—  Jurassic 434 

—  Silurian 320 

Crnziana  bilobata 303 

Ctenacanthus MB 

—  vetustus 837 

C'tenacodon  serratus 467 

Ctenopistha  antiqua 333 

Cuneolina  pavonia 471 

Cupriferous  veins 239 

( 'yuthophylloid  corals 304 

Cycadeoidea  megalophylla 428 

Cycads,  Triassic 415 

Cycas  circinalis 428 

—  cross-section  of  stem 370 

Cyclopteris  Jacksoni 330 

—  obtusa 330 

Cyprea  Matthewsonii 481 

Cypris 394 

Cyrtolites  compressus 317 

Dyeri 317 

Trentonensis 317 


Dadoxylon  Ouangondiannm 330 

Dalmania  limulurus ...  324 


PAGE 
Dalmania  pleuropteryx 321 

—  punctata 334 

Dames 445 

Dana. .  .34,  40,  42,  40,  51,  89,  224,  225,  382,  401,  452 

Daonella  Lominelli 417 

I)'  Archiac ' 50 

Darwin,  C 150 

Darwin,  G.  W 168 

Daubeny 380 

Daubree 222,  224,  227 

Dav  is 269 

Dawkins 345 

Dawson,  J.  W 3,W,  370,  401 

Dawson,  G.  M 473 

Dawsonella  Meekii 394 

Decay  of  rocks 7 

De  la  Bcche 240,  275 

Delesse 224 

Deltas 26 

formation 28 

rate  of  growth 29,  30 

Dendrerpeton 401 

—  Acadeanum,  jaw  and  tooth 402 

Dendrograptus  Hallianus 309 

Denudation 273 

agents 273 

amount 274 

geological  time  estimated  by 276 

Deposits,  chemical  in  seas. 82 

from  icebergs 72 

—  from  wave-action 39 

in  lake* 79,  81 

—  in  springs 77 

—  shell 160 

137 
136 
137 


Depression  of  coast  of  South  Atlantic  States 

of  deltas  of  rivers 

of  earth-crust  in  Pacific  Ocean 

Devonian  age,  anticipations 

age,  division  into  periods 

age,  life-system 

—  age.  physical  geography 

animals 

brachiopods 

cephalopods 

corals  

— *-  Crustacea 

fishes . . . 


327 


fishes,  general  characteristics 

fishes,  nearest  living  allies 

fishes,  rank 

insects 

land-plants 

—  plants 

• radiates 

system 

system,  area  in  United  States. . . 

Diabase 

Diatoms  of  Tertiary 

Diatryma  gigantea 

Diccras  arietina 

Diclonius  mirabilis 

Dicotyledons,  first  appearance 

Dictyopyge  macrura 

Dicynodon  lacerticeps 


340 
339 
I J2 
334 


827 
327 
204 
510 
521 
429 
499 
477 
457 
420 


628 


INDEX. 


PAGE 

Didymograptus  V-f ractns 308 

Dikes,  definition 209 

age,  how  determined 212 

effect  on  intersected  strata 210 

—  radiating,  of  volcanoes 94 

Dinichthys  Terrellt 335 

Dinoceras  ruirabile 532 

—  skull  and  brain 538 

Dinocerata 532 

Dinornis  elephantopus 605 

giganteus 604 

Dinosaurs 439,  460 

Dinotherium  giganteum,  head 525 

Diorite 203 

Dip,  definition 176 

Diphyphyllum  Archiaci 331 

Diplacanthus  gracilis 337 

Diplocynodon  victor 467 

Diplograptus  pristis 308 

—  simplex 299 

Diprotodon  Australis,  skull - 588 

Dirt-beds,  Jurassic 425 

Discoidea  cylindrica 478 

Disintegration  of  rocks 5 

Divides,  migration 272 

Dodo •. 605 

Dolerite 208 

Dollo 441 

Drift 546 

in  relation  to  gold 600 

theory  of  origin 551 

timber • 143 

Dromatherium  sylvestre,  jaw 458 

Drumlins 547 

Dryptosaurus 485 

Dunes 8 

Dutton 131,  216,  230,  264,  272 


Eads 33 

Eagres 32 

Earliest  reptiles,  general  observations 404 

Earth,  constitution  of  the  interior 84 

crust  of,  definition 166 

crust  of,  thickness 85 

crust  of,  gradual  oscillations 133 

crust  of,  means  of  geological  observa- 
tion   166 

—  density , 165 

—  form 163 

general  surface  configuration 167 

Earthquake  bridges 124 

depth  of  focus 128 

determination  of  epicentrum 130 

determination  of  focus ,  131 

effect  of  moon  on 132 

—  fissures 124 

great  sea- wave 125 

phenomena,  explanation 117 

relation  to  seasons  and  atmospheric  con- 
ditions   133 

shocks  less  severe  in  mines 124 

shocks  more  severely  felt  in  mines 123 


PAGE 

Earthquake  wave,  spherical,  determination 
of  velocity  ................................  116 

—  waves,  definition  .......................  lie 

—  waves,  their  kinds  and  properties  .......  114 

—  waves,  velocity  .........................  119 

Earthquakes  ................................  ill 

-  connection  with  other  forms  of  igneous 
agency  ....................................  ill 

-  circle  of  principal  destruction  ..........  123 

—  elevation  or  depression  during  .....  112,  134 

—  explosive  ...............................  117 

-  frequency  ..............................  Ill 

--  horizontally  progressive  ................  118 

—  minor  phenomena  ......................  122 

-  motion  .................................  122 

--  originating  beneath  ocean  ..............  125 

—  proximate  cause  ........................  114 

—  sounds  ........................  .........  122 

-  ultimate  cause  ..........................  113 

-  vorticose  ....  .......................  ....  120 

Echinoderms,  Carboniferous  ................  391 

-  Cretaceous  .............................  478 

-  Jurassic  ................................  428 

-  Silurian  ................................  309 

—  Triassic  ................................  416 

Echinorachnis  Brewerianus  .................  513 

Edestosaurus  (clidastes)  .....................  486 

Edestes  minor  .  .  ............................  398 

Elephas  Americanus  ........................  581 

-  antiquus  ...............................  580 

-  Falconeri  ...............................  580 

—  •—  Ganesa  .................................  526 

-  Melitensis  ..............................  580 

-  meridionalis  ............................  580 

-  primigenius  ............................  580 

Elevation  and  depression  of  earth's  crust, 

gradual  ...................................  133 

—  theories  ................................  138 

—  Babbage's  theory  .......................  138 

-  general  theory  ..........................  139 

—  Herschel's  theory  .......................  139 

-  gradual,  in  Greenland  ..................  136 


-  gradual,  in  Italy 


134 


-  gradual,  in  Scandinavia  .................  135 

-  gradual,  in  South  America  ..............  134 

-  of  Northern  Europe  in  Glacial  epoch.  .  .  570 
Elk,  Irish  ...................................  579 

Elvanite  ....................................  206 

Emmons  ....................................  457 

Enaliosaurs  .................................  437 

Encrinus  liliformis  .........................  .  416 

Endlich  .....................................  211 

Engis  skull  .................................  609 

Entomostraca  ...............................  325 

Eocene  basin  of  Paris  .......................  523 

—  epoch  .  .................................  502 

-  lower,  mammals  ........................  529 

-  marine,  of  Alabama  ....................  528 

-  middle,  mammals  ......................  532 

—  Tertiary  shells  ...............  ...........  512 

Eohippus  ...................................  540 

Eosaurus  Acadianus  ........................  403 

Eoscorpius  carbonarius  .....................  397 

EozoOn  Canadense  ..........................  238 


INDEX. 


629 


PAGE 

Ephemera,  larva 453 

Epicentrtim,  determination 130 

Equus 541 

Eras 281 

—  prehistoric 285 

Erosion,  average 10,  275 

—  by  glaciers 55 

—  by  rain  and  rivers 10 

—  general 273 

—  glacial,  some  general  results 573 

—  examples  of  great 12 

—  of  continents,  rate 10 

Erosive  power  of  water,  law  of  variation 11 

Eruption,  modes  of 208 

Eruption  of  volcanoes 89 

Eruptive  rocks 206 

Eryon  arctiformis 434 

—  Barrovensis 434 

Estuaries 31 

—  deposits  in 82 

—  mode  of  formation 81 

Etna,  volcano 88 

Etimicrotis  Hawnii 411 

Euomphalus  subquadratus 895 

Euphoberia  armigera 897 

Euprofips  Dana; 896 

Eurypterids,  Devonian 833 

—  Silurian 826 

Eurypterus  remipes 825 

Evolution,  general  process 280 

in  geologic  history 280 

—  of  coal  plants 872 

—  of  early  reptiles 404 

—  of  early  birds 444 

of  early  mammals 448,  688 

of  organic  kingdom,  illustrated  by  De- 
vonian fishes 843 

—  the  central  idea  in  geology 405 

Ewing 129 

Exogyra  Texana 479 


Fagns  ferruginea  ............................  508 

—  polyclada  ..............................  475 

Faults  .......................................  228 


—  in  coal-measures  .......................  349 

—  law  of  slip  ..............................  231 

-  two  kinds  ..............................  231 

Fauna  and  flora,  geological  ..................  195 

-  first  distinct  ............................  801 

-  Quaternary  mammalian,  in  North  Amer- 
ica ........................................  581 

—  Quaternary  mammalian,  of  England.  :  .  .  581 

-  still  changing  ...........................  605 

Favosites  hemispherica  ..............  .......  331 

Favre  ...................................  256,  473 

Faye  ........................................  169 

Feldspar  .................................  7,  204 

Felisatrox  .................................  682 

Fenestella  elegans  ..........................  810 

Ferns,  coal  ..................................  362 

Ficus  pyriformis  ..........................  513 


PAGE 

Fingal's  Cave 213 

Fiords,  how  formed 573 

Fire-clay 347 

Fire-damp £56 

Fisher 100.  264 

Fishes,  age  of -. 327 

Cretaceous 482 

Carboniferous 398 

—  Devonian 334-344 

Jurassic 436 

—  sudden  appearance 344 

—  Tertiary 518 

—  Trias*  ic 416 

Fissures 227 

cause 228 

Flabellina  rugosa 471 

Flint-flakes  from  Miocene 608 

Flint-veins  in  gneiss 5 

Flood-plain  deposits 24,  557 

Florida  reefs 156 

—  compared  with  other  reefs 159 

formation 157 

history  of  changes 157 

Fluor-spar /"/...  236 

Flustra  truncata 309 

Folding 174 

Fontaine 477 

Foraminifers 161 

of  chalk '.471 

shells  of  living 472 

Forbes's  theory  of  glaciers 61 

Forbesiocrinus  Worthcni 802 

Fordilla  Troyensis 890 

Forel 49 

Forest,  fossil,  ground  plan  of  Carboniferous.  375 

fossil,  Jurassic 425 

Formation,  geological,  definition 181,  190 

Formica  lignitum 514 

Fossils,  definition 189 

degrees  of  preservation 191 

distribution  in  strata 194 

increasing  likeness  to  existing  forms.. . .  196 

nature  determined  by  age 195 

nature   determined  by  country  where 

found 195 

nature  determined  by  kind  of  rock 194 

origin  and  distribution 190 

—  primordial.  American 299 

primordial,  foreign 300 

stratified  rocks  classified  by  means  of . .  198 

Fouqud 116 

Fractures 227 

Free  crinoid,  living 311 

Frost,  geological  action 8 

Fusing-point,  not  the  same  for  all  depths  in 

earth..  86 


Gabbro 204 

Gailenreuth  Cave 676 

Galerites  albogalerus 478 

Galesaurus  planiceps 420 

Ganges,  average  erosion 11 


630 


INDEX. 


PAGE 

Ganocephala 403 

Ganoids,  Carboniferous 402 

—  Devonian 335 

Jurassic 436 

Gar-fish .338 

Gas,  smoke,  and  flame  from  volcanoes 93 

natural 386 

Gasteropods,  Carboniferous 392 

Devonian 333 

—  Cretaceous 480 

—  Silurian 316 

—  Tertiary 511 

Gastornis  Edwardsii 521 

Gault 424 

Geikie 254 

Genesis  of  existing  orders,  families,  etc 539 

Geographical  Fauna  of  Quaternary  times 575 

Geological  chronology,  mode  of  construct- 
ing    199 

—  fauna  and  flora  differ  more  than  geo- 
graphical   187 

horizon,  definition 196 

observation,  means 166 

—  period,  tested  by  life-system 196 

period,  tested  by  rock-3ystem 196 

Geology,  definition 1,2 

departments 1 

dynamical 3 

—  historical 279 

structural .' 163 

German  Ocean,  tides 43 

Geysers,  Bunsen's  artificial 110 

—  theories  of  eruption 106 

-. —  Bunsen's  investigations  of 107 

—  definition 101 

description 101 

—  Mackenzie's  theory 106 

—  phenomena  of  eruption 103 

—  of  the  Yellowstone 103 

Giant's  Causeway 213 

Gibson 422 

Gigantitherium  caudatum 455 

Gilbert 9,  14,  80,  113,  211,  232,  288,  423 

Ginko,  evolution 361 

Ginkophyllum 361,  412 

Glacial  epoch 545,  546 

climate,  Croll's  theory 590 

climate,  Wallace's  views 592 

—  epoch,  first 563 

—  epoch,  drift-materials 546 

—  epoch,  in  Europe 570 

—  epoch,  second 570 

erosion,  general  results 573 

lakes 58,  574 

— -  scorings 57,  549 

—  times  in  America,  probable  condition 
during 552 

valley,  section  across 58 

Glaciatio'n 57,  549 

Glacier,  great  RhSne 571 

Glaciers,  advance  and  retreat. 48 

as  a  geological  agent 55 

—  conditions  necessary  for 46 

definition .  45 


PAGE 
Glaciers,  irregularities  of  surface 51 

—  earth  and  stones  on  surface 53 

evidences  of  former  extension 58 

fissures 67 

—  general  description 50 

—  graphic  illustration 48 

—  in  Western  North  America 563 

line  of  lower  limit 49 

—  motion 48 

motion  and  its  laws 59 

—  motion,  theories  of 61 

—  Croll's  theory  of 65 

—  Forhes's  theory  of 61 

Thompson's  theory  of 66 

—  Tyndall's  theory  of 63 

—  physical  theory  of  veins 69 

—  ramifications 46 

structure 66 

—  transporting  power 57 

veined  structure 68 

Glaphyroptera  gracilis 435 

—  pterophylli 417 

Globigerina  bulloides 162,  472 

ooze 102 

Glyptocrinus  decadactylus 312 

Glyptodon  clavipes 587 

Glyptolemus  Kinairdii 337 

Gneiss 220 

—  decay 7 

Gold,  auriferous  veins 241,  247 

drift  in  relation  to 600 

Goniatites,  crenistria 395 

—  lamellosus 333 

..  395 


Lyoni . 


Goniopygus  major 

Goodfellow 

Gorges,  how  formed 

Gossan 

Grand  Caflon  of  the  Colorado 

Granite,  decay '. 

—  graphic. 

origin 

—  porphyritic 

syenitic 

veins 

Granitic  rocks,  chemical  composition   and 

kinds 

rocks,  mode  of  occurrence 

Graphite 

Graptolites 

Clintonensis 

Graptolithus  Logani 

Greenland  coasts 

Green  River  Basin,  Wahsatch  beds 

—  River  Basin,  Bridger  beds 

Greensand ' 

Green-stones 

Gryphsea  calceola 

—  Pitcheri 

—  speciosa 

Gulf  Stream,  probable  agency  in  forming 

reefs , 

Guppy 

Guyot 


473 
113 

15 
239 

17 
7 

203 
223 
203 
203 
205 


204 
354 
308 
303 
308 
136 
530 
532 
474 
206 
458 
479 
460 

159 
160 


IXDEX. 


631 


Gyranophiona 

Gypsum  deposited  from  springs. 
Gyracanthus 


PAGE   I  PACK 

.  402  !  Hymenophyllites  splendens 864 

..    79     Hyolithes  primordialis 299 

. .  398     Hyrachyus 533 


H 

Hadrosaurus 485 

Hall 407 

Halodon  sculptus 500 

Halysites  catenulata '. . .  306 

Hamilton  period 328 

llamites 480 

Haughton. .   187 

Hay 4*1 

Hayden 968 

Heavy  spar 236 

Hedera'pjiylluin  angulatum. 478 


II. 


425 


Heiioceras  Robertianus 482 

Heiuerobioides  gigantcus 435 

Hemicidaris  crenularis 489 

Hemitelites  Brownii 427 

ilenessey 164 

Ucnchel 34,  35,  39,  74,  88,  80, 180 

—  theory  of  movements  of  earth's  crust. . .  132 

Hesperornis  regalis 490 

Heterocrinus  simplex 313 

Uilgard 31 

Hill 478 

Hipparion 541 

—  gracile,  restored 526 

Hippnrites  Toucasiana 480 

Hitchcock 452 

Holme* 211 

Holoptychiiw  Hibberti,  tooth 899 

nobilissimus 836 

Homocrinus  scoparius 813 

Hopkins 86 

Horizon,  geological 196 

Hornblende 204 

Hornblende  schist 220 

Horse 237 

Horse  family,  diagram  of  changes 542 

genesis 540 

Howell 232 

Iliimboldt 83,  85 

Humphrey 11 

Humus  acid 4 

Hunt,  E.  B 382 

— ,  T.  S 224,882 

Huronia 818 

Ilnxley 403,  450 

Ilybodus  apicalis 418 

reticulatus,  spine  and  tooth 436 

Hydrographical  basin 10 

Hydrothermal  fusion 91,  222 

Hydrozoa,  living 307 

Silurian 308 

Hyena  spelaea,  skull 578 

Hylaeosaur 441 

Hylerpeton 403 

Hylonomus 403 

Hymenocaris  vermicauda 800 

Hymenophyllites  aiatus 364 


I 

Ice,  agency  of 45 

—  floating 70 

Icebergs  as  a  geological  agent 72 

—  deposits  from 72 

—  formation 70 

—  number 71 

Ice-cliffs  containing  remains  of  mammoth.. .  580 

Ice-pillars,  formation 51 

Ice-sheet,  limit  moraine 554 

Ichneumon  inf emails 514 

Ichthyocrinus  sublajvis 812 

Ichthyornis 489 

—  dispar 490 

—  victor 489 

Ichthyosaurs  of  Jura-Trias 466 

Ichthyosaurus  communis 437 

—  paddle-web 438 

Igneous  agencies 83 

Igneous  rocks,  classification 202 

'Iguanodon 440 

—  Bernessartensis .' 441 

Imhoffla  pallida 514 

Inachus  Kaempferi 326 

Infusorial  earth,  Richmond 510 

earths,  origin 511 

Inoceramus  diniidius 478 

Insects,  Carboniferous 397 

—  Devonian 334 

—  Jurassic 435 

—  Tertiary 514 

Intercalary  beds 211 

Interior  heat  of  the  earth 83 

—  of  earth,  increasing  temperature 84 

—  of  earth,  rate  of  increase  of  tempera- 
ture      85 

Interval  between  Archaean  and    Palaeozoic 

eras 294 

Intrusive  rocks 205 

Invariable  temperature,  stratum  of 83 

Invertebrates,  age  of 996 

Irish  elk,  skeleton 579 

Iron  age 607 

—  hat  of  copper  vein : 289 

ore  of  the  coal-measures 883 

—  springs,  deposits  in 79 

Irving 223 

Islands,  coral '46 

bordering 45 

mangrove 158 

Isogeotherm 84 

Isopods 325 

Isotelus  gigas 323 


Jointing,  regular,  of  limestone 227 

Joints 182,  226 

Judd 


632 


INDEX. 


PAGE 

Jakes 286 

Julian 4 

Jupiter  Serapis,  temple  of 135 

Jura  Mountains,  section 424 

Jurassic  animals 428 

ammonites 430 

belemnites 432 

birds 444 

—  cephalopods 428 

coal-measures 425 

Crustacea 434 

fishes 436 

insects 435 

— -  mammals 448 

period 424 

plants 426 

—  reptiles 437 

Jura-Trias,  bird-tracks 454 

distribution  of  strata 451 

disturbances  which  closed  it 468 

ichthyosaurs 466 

in  America 450 

life-system 452 

mammals .' .  467 

of  Connecticut  Valley 452 

of  interior  plains  and  Pacific  coast 458' 

of  Richmond  and  North  Carolina  coal- 
fields  456 

physical  geography  of  America  during. .  467 

plants 459 

tracks,  reptilian 454 


Kames 547 

Kaolin,  formation 7 

Kilauea,  volcano 87 

Kimmeridge  clay 424 

King 211,  229,  257,  276,  409,  469 

King-crab,  larva 324 

Kitchen-middens 613 

Krakatoa 89 

Krummell 167 

Kutorgina  pannula 299 


Labyrinthodonts 404,  418 

—  teeth 404,  419 

Laccolites 211 

Lagoonless  islands 149 

Lake-dwellings 613 

Lakes,  alkaline 79 

—  chemical  deposits  in 79 

flooded 556 

glacial 

glacial,  origin 575 

history  of  the  great 560 

salt 80 

Lake  Agassiz 556 

Bonneville 566 

Mono 366 

Lahontan 566 

Superior,  effect  of  waves  on  shore 36 

Tahoe,  map  of  southern  end 565 


PAGE 

Lamellibranchs 313 

Carboniferous 395 

Cretaceous 478 

Devonian 333 

—  Jurassic 428 

Silurian 316 

Triassic 417 

Lamination,  oblique  or  cross 174 

Lamna  elegans 518 

Land  formed  by  oceanic  agencies 44 

Land-surfaces  and  sea-bottoms,  cause 167 

Langley 381 

Laosaurus  altus 463 

Laramie  animals 498 

—  epoch 495 

—  group,  area 497 

—  plants 497 

Laurentian  rocks,  evidences  of  life 288 

area  in  North  America 287 

system  of  rocks 285 

Laurus  Nebrascensis 477 

Lava 90 

—  composition 92 

fields...  ..  506 


hardened . , 

sheets 

Lead  veins. 

Lebias  cephalotes 

Leidy 

Legumenosites  arachioides 

Lepadocrinus  Gebhardii 

Lepidodendrids '. 

Lepidodeudron 

compared  with  club-moss 

corrugatum 

—  diplotegioides 

—  Gaspianum 

ideal  section 

modulatum 

politum 

rigens 

Lepidoganoids,  Devonian 

Lepidophloios  Acadianus 

Lepidosiren 

Lepidosteus 

Lepidostrobus 

Lesley 

Lesquereux 304,  379, 

Lestornis  crassipes 

Lestosaurus  simus 

Levies,  natural  and  artificial 

Lewis,  C.  A.  W 

Lias 

Libellula. . . 


210 
240 
519 
485 
496 
312 
365 
365 
367 
366 
366 
330 
367 


475 

490 

487 


424 
435 


574_LichasBoltom. 


Life-system  a  test  of  formation 196 

Lime-accumulations 145 

Limestone  caves 76 

concretions 188 

decay 7 

nummulitic 512 

Limnerpeton  laticeps 412 

Limnohyus  (Palaeosyops) 534 

Limuloids. . .  . .  325 


INDEX. 


633 


PAGE 

Limnlus  Moluccanu? 326 

—  trilobitc  stage 334 

—  young 324 

Lingula  anatina 314 

Lingulella  celata 299 

—  ferruginea 300 

Liparite 207 

Liquidarabar  integrifolium 474 

—  Europeum 509 

Lisbon  earthquake 126 

LithodomuH 135 

Lithostrotion  Califuruienee 391 

Lituites  cornu-arietis 320 

—  Graf  tonensis 820 

Lituola  nautiloides 471 

Loess,  origin 559 

Logan 285,  886 

Lousdaleia  floriformis 306 

Lwkout  Mountain 267 

Lower  Helderberg  period 296 

Loxolophodon 532 

Lucina  Ohioensis. 333 

Lycosaurus 420 

Lyell ......  26,  89,  136,  143,  164,  217,  375,  401,  473 

Lymnohyus 532 


McOee 478 

Machseracanthus  major 887 

Machaerodus  cultridens 527 

—  latidens 577 

—  necator 585 

McKenzie 

Macrocheilus  Newberryi 

Macrourans 

Maelstrom 

Malacostraca 

Mallet....  100,  111,  116,  118,  123,  131,314, 
Mammals,  age  of 

Cretaceous 

—  Eocene 

Genesis  of  orders 680 

Jurassic 448 

Laramie 600 

origin 449 

—  Triassic 421 

—  first,  affinities '. 44fl 

of  Tertiary,  general  remarks  on 538 

—  of  Jura-Trias 467 

Mammoth 580,  5*3 

—  dr;i\ving  of,  by  contemporaneous  man..  612 
Man,  age  of 603 

—  antiquity 607,  618 

—  Miocene,  supposed 608 

Neolithic 618 

—  Pliocene,  supposed 608,  614 

—  primeval,  character 619 

—  primeval,  in  America 614 

—  in  Europe 608 

—  Quaternary 609,  616 

Mangrove  Islands  in  land- formation 158 

Marble 220 

Marcou ..473 


100 

MB 
fl 


501 

I'.ts 

:,.:{ 


9 

183 


PAGE 

Mariacrinus  nobilissimns 313 

Marly  soil,  formation 7 

Mareh.. . .  284,  403,  443,  445,  457,  460-462,  466. 

467,  485,  486,  488,  491 
Marshes  and  bogs,  Quaternary  mammals  in 

580,  582 

Marsupials 449 

Mastodon  Amcricanus 582 

Maatodonsaurus  Jajgeri 418 

Mauna  Loa.  volcano as 

Mauvaises  Terres 208,  504 

Miocene  mammals 535 

Mechanical  agencies  of  the  atmosphere K 

—  agencies  of  water 

—  theory  of  slaty  cleavage,  Sharped 

Medlicot '.'»; 

Megalonyx,  claw-core 586 

Megalosaurus 441 

Megaphyton 362 

—  leaf-near  of 3(15 

Megatherium  Cuvieri 586 

—  mirabilis 584 

Melania  Wyomingensis 45)8 

Mehan 51 

Mentone  skeleton 610 

Mesas 17 

Mesohippua 541 

Mesopithecus  Pantelici 527 

M«  -i./oic  animals 416 

....  414 

49t 

....  414 

....  4U4 

...  226 


era. 


era,  disturbance  which  closed 

era,  subdivisions 

—  general  observations 

Metadiorite 

Metamorphism 

alkali  as  agent 

crushing  as  cause  of  heat  in 

explanation  of   phenomena  aitocUitod 

with 

general 

.heat  as  agent 

—  local . . 


mechanical 

—  pressure  as  agent 

theory 

—  water  as  agent 

Metasyenite 

Mer  de  Glace 

Miamia  Dan» 

Mica-schist 

Microlestes  antiquus 

Milne Ill,  122, 

Minnehaha  falls 

Mineral  veins 

Mines,  placer 

Miocene  epoch 

insects 

mammals  of  Siwalik  Hills 

—  man,  supposed 

of  Nebraska 

shells,  California 

Miohippus 

Mississippi,  delta 

erosion  by 


221 
£21 
226 

55 
397 
220 
421 
131 

14 
234 
240 
502 
514 


535 

513 

541 

27 

11 


634 


INDEX. 


PAGE 

Mississippi,  flood-plain 24 

River,  history • 561 

Modiolopsis  solvensis 300 

Mollusks,  age  of 293 

—  Cretaceous 478 

—  Silurian 313 

Monkeys 528 

Monoclinal  axes 178 

Monograptus  priodon. . . ' 308 

Mono,  Lake 80 

Monotremes 449 

Mont  Blanc  glacier  region 47 

Monticules 90 

Moraines 54 

in  Colorado 565 

—  of  ice-sheet 553 

Morosaurus  grandis 461 

Mosasaurs 486 

Mosasaurus  princeps 487 

Mosely 65 

Moulins 53 

Mountain-ranges,  age 261 

cause  of  pressure  producing 263 

—  fissure-eruptions  in 262 

—  general  form,  and  how  produced 251 

history  of 261 

made  of  thick  sediments 257 

metamorphism 256 

monoclinal 264 

—  ranges,  occurrence  of  fissures,  slips,  and 
earthquakes  in 262 

—  once  marginal  sea-bottoms 258 

—  proof  of  elevation  by  lateral  pressure. . .  253 

structure  and  origin 250 

volcanoes  in 263 

Mountain-formation,  rate 261 

Mountain-forms  resulting  from  erosion 267 

Mountain-origin 251 

Mountain-sediments,  thickness 257 

Mountain-sculpture 266 

Mountain-structure 252 

Murchisonia  gracilis 316 

Murray 152 

Myalina  Permiana 411 

Mylodon  robustus 587 

left  hind-foot 615 

Myophoria  lineata 417 

Myrmica  tertiaria 514 


N 

Naiadites 394 

Nanosaurus  agilis 462 

Nautilus  pompilius 317 

Neanderthal  skull 610 

Neolimulus  falcatus 396 

Neolithic  age 607 

—  man 613 

Neuropteris 458 

—  flexuosa : 363,  364 

hirsuta 364 

—  linsef olia 458 

—  polymorpha 330 

Newberry 247,  287,  335,  337 


PAGE 

Newfoundland,  Banks  of 44 

Niagara  Falls,  description 12 

gorge,  time  necessary  to  form 15 

—  period 296 

Nile,  flood-plain 24 

delta 27 

Nodular  or  concretionary  structure 188 

Nodules,  flattened  by  pressure 190 

—  flint,  in  chalk-cliffs 190 

form 189 

—  kinds  found  in  different  strata. 190 

Noeggeratria 361 

Norfolk  cliffs,  effect  of  waves  on 37 

NordenskiOld 494 

Norway,  effect  of  waves  on  the  coast 38 

Notidamus  primigenius 518 

Nototherium  Mitchell! 588 

Nummulina  laevigata 511 

Nummulitic  formation 512 


Obolella  crassa 299 

: sagittalis 300 

Obsidian 207 

Oceanic  agencies,  land  formed  by 44 

—  currents,  geological  agency 42 

—  theory 39 

Ocean-waves,  effect  of 34 

Ochsenius 423 

Odontolcse 491 

Odontopteris  gracillima 364 

—  Wortheni 364 

Odontopteryx 521 

—  toliapicus,  skull 521 

Odontornithes 491 

Odontotormse 491 

Oil-bearing   strata  of   the   Eastern   United 

States 388 

Oil-formations 387 

Oldhamia  antiqua  : 300 

Olenus  mucrurus 300 

Olenellus  Gilbert! 299 

Oligoporus  nobilis 393 

Onychaster  flexilis 393 

Onychodus  sigmoides 335 

OOlite 424 

OQlitic  limestones,  origin 424 

Ooze,  deep-sea 472 

globigerina 162 

Ophiderpeton 403 

Ophiomorpha 400 

Orange  sand.  Mississippi 547 

Orbulina  universa 162,  472 

Orders,  genesis  of  existing 539 

Oreodon , 535 

Ores 236 

metallic,  formation 245 

Organic  agencies 140 

remains,  decomposition  prevented 191 

Organisms,  progressive  change  in 406 

Ormoceras 318 

tenuifilum 319 

Ornithes.  .  491 


INDEX. 


635 


PAGE 

Ornithotarenp 485 

Orodus  mammilare 399 

Orohippus 541 

Orthis  Davidsonii 315 

_  Hicktui 300 

—  Livia 332 

—  porcata 315 

Orthisina  transversa 299 

Orthoceras  Duseri 319 

medullare 819 

—  multicameratum 319 

restoration 318 

—  vertebrale 319 

Orthoclase 203 

Orthoceratite 31? 

Ortliont'ina  Xew  berry  i 833 

Orthonota  parallela 816 

Orton 887 

Osborn 450,  457 

Osmeroides  Mantelli 484 

OsU-olepis 337 

Ostrea  Caroliniensis 514 

—  Georgiana 512 

1 1 1 1 1  :i  •  •  1 1  - ;  > 478 

—  Marehii 480 

—  sellaef  ormis 512 

—  Sowerbyi 430 

—  Titan 513 

Otodus 488 

Otozamites  Macombii 459 

Otozoum  Moodii 454 

Oudenodon  Bainii 420 

Outcrop 177 

Owen 419,  421 

Oxford  clay 424 

Oyster,  first  appearance 428 


Pachyderms '. 539 

Pachypteris  lanceolate 427 

Pachytherium 667 

Palieaster  Shaefferi 313 

Paloeocarus  typus 396 

Palaeolithic  age 607 

Palaeoniscus  aculeatus 396 

restoration 412 

Palteophonus 511 

Palseopteris,  leaf-scars 365 

Palseopternus 826 

Palaeosyops 532 

Pala?otherinm  magnum 523 

Palaeozoic  era 282,  289 

era,  chemical  changes  during 405 

—  era,  general  observations 405 

era,  physical  changes  during 405 

—  era,  physical  geography  on  American 
Continent 292 

era,  subdivisions 293 

—  fauna  compared  with  Neozoic 407 

—  rocks,  area  in  the  United  States 291 

rocks,  thickness 290 

times,  general  picture 407 

transition  from,  to  Mesozoic 409 


PAGE 

Paradoxides  Bohemicns 301,  324 

—  Harlani 301,  324 

Paris,  Eocene  basin 523 

Peat,  alternation  with  sediments 143 

—  bogs  and  swamps 140 

—  composition  and  properties 141 

—  mode  of  growth 141,  142 

Pecopteris  f alcatus 458 

—  Strongii 303,  304 

Pecten  cerrocensis 513 

—  fibrosus 430 

—  nuperum 512 

—  Valoniensis 417 

P616's  Hair 91 

Pemphyx  Sueurii 417 

Peneroplis  planatus 162,  472 

Pentacrinus  Caput-Meducae 310 

Pentamenis  Knightii 315 

Pentremites  Burlingtoniensis 392 

cervinus 392 

gracilis 892 

—  pyriformis 892 

P6rigord  caves 612 

Periptychus  rhabdodon 530 

Perissodactyls 539 

Permian  period .'. .  409 

—  reptiles,  affinities 413 

—  rocks,  area  in  United  States 413 

—  shells 411 

Pe  rry Ill 

Petalodus  destructor 399 

Petrifaction 191 

—  theory  of 192 

Petroleum,  geological  relations 386 

kinds  of  rocks  which  bear 888 

laws  of  interior  distribution 887 

origin,  theories  of 880 

origin  of  varieties 890 

Phacops  latif rons 834 

Phascolotherium 448 

Phenacodus  primaevus 530 

Phillips,  A 246,  247,  248,  249 

,  J 78,  232,  273,  347 

Phillipsia  Lodiensis 396 

Phonolite 208 

Phryganea  cases 516 

Phyllocladus 359 

Phyllograptus  typus 808 

Phyllopods 325 

Physical  geography  of  America  and  Europe 

compared •  345 

Pine-cone,  Jurassic 427 

Placer-mines 240,  001 

Placoderms 339 

Placo-ganoids 339 

Placoids,  Carboniferous 399 

Cretaceous 482 

Devonian 335,  337 

distribution  in  time 484 

Jurassic 486 

—  Tertiary 513,  514 

Plagioclase 204 

Plagiaulax 448 

Plants,  Carboniferous 358 


636 


INDEX. 


PAGE 

Plants,  Cretaceous 476 

Devonian 327,  329,  330 

Jurassic 429,  431 

—  of  Jura-Trias 460 

Silurian 304 

—  Tertiary 518 

Platanus  aceroides 509 

Platephemera  antiqua 334 

Platysomus  gibbosus 412 

Plesiosaurus 438 

—  dolichodeirus 437 

Pleuracanthus 398 

Pleurocystites  squamosus 312 

Pleurophorus  subcuneatus 411 

Pleurotomaria  agave 316 

—  dryope 316 

scitula 395 

Pliocene  epoch 502 

—  man,  supposed 608 

Pliohippus 541 

Pliosaurus 439 

Plumbiferous  veins 240 

Plumularia 307 

Plutonic  rocks 203 

Po,  river 26 

Pocket 236 

Podogonium  Knorrii 509 

Podozamites  crassifolia 459 

—  Emmonsi 415,  457 

Polypterus 338 

Polyzoa,  living 309 

—  Silurian 309 

Ponera  veneraria 514 

Populus  cuneata 496 

Porphyrite 206 

Portheus  niolossus,  tooth 483 

—  restored 484 

Potomac  formation 473 

Potsdam 296 

Powe,ll 229,  232,  255,  271 

Prestwich 53,  101,  283 

Primary  rocks 289 

Primeval  man,  character 619 

in  America 614 

—  in  Europe 608 

Primordial  beach  and  its  fossils 298 

—  period 296 

Prionastrea  oblongata 429 

Proboscidians 525,  540 

Prodryas  persephone 517 

Productus  mesialis 394 

—  punctatus 394 

Propylite 207 

Protaster  Sedgwickii 313 

Protaxites 329 

Protohippus 541 

Protophyllum  quadratum 475 

Protozoa,  Cretaceous 477 

Silurian 304 

Protypus,  Hitchcocki 299 

Peeudocrinus 312 

Psilophyton  princeps 330 

Psychozoic  era 603 

Pteranodon . . .  ..  486 


PAGE 

Pteraspis 336 

Pterichthys  cornutus 336 

Pterodactyl 442 

Pterophyllum  comptum 427 

Jaegeri 415 

Pteropods,  Silurian 300 

Pterosaurs 442,  485 

Pterygotus  Anglicus 325 

Gigas 326 

Ptychodus  Mortoni 483 

Ptyonius 403 

Puerco  beds 529 

Pumice 92 

Pupa  vetnsta 394 

Puzzuoli,  temple  of  Jupiter  Serapis  near 135 

Pyrites,  copper '..: 239 

—  iron 240 

Pythonomorpha 486 


Quartzite 220 

Quartz  veins,  auriferous 240 


in  gneiss. 


Quaternary,  a  period  of  revolution 594 

climate,  cause 589 

climate,  CrolPs  theory 590 

—  mammalian  fauna  of  England 581 

—  mammalian  fauna  in  North  America. . . .  581 
man 609 

—  period 545 

—  period,  cause  of  climate 589 

—  period,  characteristics 545 

—  period  in  Australia 588 

—  period  in  Eastern  North  America 546 

—  period  in  Europe 569 

—  period  in  South  America 584 

—  period,  mammals 575 

—  period,  migration  of  species  during 595 

period  on  the  western  side  of  America. .  562 

period,  plants  and  invertebrates. 575 

period,  subdivisions 545 

period,  time  involved  in 593 

period,  general  observations 589 

—  times,  geographical  fauna 588 

Quercus  crassinervis 508 

—  primordialis 474 

Saffordi 508 


Radiates,  Devonian 332 

—  Silurian 304 

Radiolites  cylindriasus 480 

—  mammellaris 480 

Rain-prints 400 

—  sculpture 12 

Raniceps 4C3 

Rankine 18 

Ravines,  how  formed 15 

Reade 234 

Recent  epoch 603 

Recent  extinct  species,  examples ~  605 

Receptaculites  f ormosus 305 


INDEX. 


637 


PAGE 

Reefs,  coral,  of  Florida 156 

—  coral,  of  the  Pacific 147 

Refuse-heaps 618 

Resolution  theory  of  glaciers,  of  Tyndall 63 

Reindeer  age 607,  611 

Renevier 254 

Reptiles,  age  of 414 

Reptiles,  Carboniferous 400 

—  Cretaceous 4*1 

—  ganoids  allied  to 34-3 

—  Jurassic 437 

—  Tertiary 519 

—  Triastnc 417 

Reptilian  footprints,  Carboniferous 400 

—  footprints  of  Jura-Trias 454 

Requienia  patagiata 479 

Texana 479 

Rhabdocarpon -360 

Rhamphorhynchtis  phyllurus 443 

Rhizocrinus  Lofotensis 310 

Rhombus  minimus 518 

RhOne,  delta 28 

Rhynchonella  eulcata 314 

—  varians 430 

Rhynchosaurs 430 

Rhyolite 307 

Rib 236 

Ribboned  structure 236 

Richtofen's  classification  of  Tertiary  erup- 

tives 218 

Rink 51,70 

Ripple-marks,  how  formed 80 

Rivers,  agency 9 

—  erosion  of 10 

—  transporting,  law  of  deposit 19 

River-beds  of  California,  old  and  new 567 

Rivers  as  indicators  of  crust-movements 186 

River-deposits,  age  of ,. . .    30 

River-gravels 594 

—  age  of  the 602 

Rivers  during  the  Quaternary  period 567 

—  erosion 9 

—  winding  course  of 23 

River-swamp 24 

River- terraces 557 

Roches  moutomi6es 56,  549 

Rock-broth 91 

Rock-disintegration 6 

Rocking  stones 6T  57 

Rock-salt,  mode  of  occurrence 422 

—  origin 421 

—  theory  of  accumulation 422 

Rock-system,  as  a  test  of  a  formation 196 

Rocks,  classes 170 

definition 170 

—  eruptive  or  volcanic 206 

igneous 201 

—  igneous,  classification 202 

—  igneous,  different  modes  of  classifying.  216 

—  igneous,  origin 215 

—  inetamorphic 219 

—  metamorphic,  principal  kinds 220 

Plutonic 203 

Plutonic,  mode  of  occurrence 204 


PAGE 

Rocks,  stratified  or  sedimentary  .............  170 

-  stratified,  cause  of  consolidation  .......  172 

—  stratified,  classification  .................  197 

—  stratified,  comparison  of  fossils  ........  198 

-  stratified,  have  been  gradually  depos- 

ited .................................  173 

—  stratified,  kinds  ........................  171 

—  stratified,  lithological  characters  ........   n>8 

-  stratified,  are  consolidated  sediments.  .  .  172 

—  stratified,  originally  nearly  horizontal.  .  173 

—  stratified,  order  of  superposition  ........  19V 

—  structure  and  position  ..................  170 

-  structure  common  to  all  ................  226 

—  trappean,  general  characteristics  ........  205 

—  trappean,  varieties  ____  .................  200 

-  unst  ratified  or  igneous  .......  ...........  201 

-  volcanic  .....................  .......  ____  206 

—  volcanic,  modes  of  eruption  ...........     208 

-  volcanic,  modes  of  occurrence  ..........  209 

Rogers  ......................................  301 

Rose  ........................................  ±>4 


|  Rotalia  concainerata  ....................  162,  472 

I  Ruminants  ..................................  539 

j  Rush  Creek,  section  on  .....................  547 

Russell  .............................  ..  423 


8 

Sabal  major 509 

Saccocoma  pectinata 429 

Sackenia  arcuata 517 

Safford 239 

Saliferoux  group 421 

Salina  period 296 

Salisburia 359 

Salix  protese  folia 475 

Salt-lakes,  formation 79 

—  deposits  in gi 

Sand-spits 44 

Sandstone,  Connecticut  River 452 

Sandstones,  decay 7 

Sanidin 208 

Sassafras  araliopsis 475 

cretaceum 475 

Mudgei 475 

Sauropoda 403 

Sauropus  primjevus 400 

Saururae . .  491 

Scalaria  Sillimani 481 

Scalea  saussureana 514 

Scandinavian  sea-beaches 135 

Scaphiocrinus  scalaris 392 

Scaphites  sequalis 482 

Scelidosanr 442 

Schists 220 

Scorpion,  Silurian 826 

Scotland,  effect  of  waves  on  coast 37 

Scudder 398 

Scrope 95 

Sea-islands 45 

Sea-margins,  old 555 

Seas,  chemical  deposits  in 82 

during  the  Quaternary  period 562 

Sea-waves  produced  by  earthquakes 125 


638 


INDEX. 


Sediments,  transportation  and  distribution,  18,  42 
thick,  material  for  mountain-ranges 257 

—  thick,  why  lines  of  yielding 260 

Seebach 132 

Seismographs 128 

Sekeya 117,  130 

Selvage 235 

Sepia,  living 432 

Sequoia  ambigua 476 

—  Langsdorfii 508 

Senarmont 224 

Serapis,  temple  of 135 

Serpentine 220 

Sertularia  pinnata 307 

Shale,  black,  of  coal-measures 347 

Sharpe 183 

Shasta,  volcano 88 

Shell-deposits 160 

Shell-mounds 613 

Shells,  bivalve  and  univalve,  Carboniferous. 

394,  395 

—  distorted 183,  184 

as  a  rock-forming  agent 161 

Permian 411 

Shore-ice 72 

Sierra  Nevada , 259,  265,  569 

Sigillaria  elegans,  leaf 368 

Grseseri 368 

— -  laevigata 368 

obovata 368 

restoration 370 

reticulata 368 

section  of  stem 370 

Sigillarids 329,  368 

Silica  deposited  from  geysers 105 

—  deposited  from  springs 79 

Silurian  age,  general  life-system 302 

age,  physical  geography 297 

—  animals 304 

—  plants 304 

—  scorpions 326 

system,  area  in  America 296 

system,  rocks 296 

system,  subdivisions 296 

Siphonia  ficus 477 

Sivatherium  giganteum 525 

Siwalik  Hills,  India,  Miocene  of 524 

Slate-rocks,  decay 7 

Slaty  cleavage 181 

Slip,  law  in  faults 231 

Smilodon 585 

Soils,  depth 5 

—  how  formed 4 

Solenomya  anodontoides 395 

Sorby 185,  225,  244 

Sorting  power  of  water 20 

Southern  coast  of  United  States,  wave-ac- 
tion      35 

Sphenophyllum  erosum 371 

Sphenothallus  angustif  olius 303 

Spirifer 416 

Cumberland!* 315 

— -  fornacula 332 

hysterica 814 


PAGE 
..  332 

..  394 
..  314 
.  .  394 
. .  333 


Spirifer,  perextensus 

—  plenus 

—  striatus 

Spirorbis 

-  Arkonensis 

—  omphalodes £33 

Sponges,  Cretaceous 477 

Springs 74 

carbonated 77 

—  chemical  deposits  in 77 

—  fissure 75 

Spy.  cave  near 610 

Squalodonts 436 

Squatina  acanthoderma 436 

Stagonolepis 520 

Stalactites 77 

Stalagmites 77 

St.  Anthony,  falls  of 14 

Stegocephali 413 

Stegosaurus  ungulatus 465 

—  stenops 466 

Sterna  cantiaca 492 

Stigmaria  flcoides 369 

Stone  age 607 

Stones,  balanced 57 

Strata,  elevated,  inclined,  and  folded 174 

—  outcrop,  definition 176 

Stratification 22,  170 

Strike,  definition 176 

Stromatopora  concentrica 305 

—  rugosa 304 

Strombodes  pentagonus 306 

Strophomena 416 

rhomboidalis 332 

Structural  geology 163 

Subangular  stones 546 

Sub-Carboniferous  period 345 

Submarine  banks 43 

Subsidence  during  the  Quaternary,  evidence  555 

—  of  Northern  Europe 572 

of  Pacific  floor 137 

of  Southern  Atlantic  States 137 

area  of  land  lost 153 

amount  of  vertical 153 

rate 154 

Sulphur  deposited  from  springs 79 

Superior,  Lake,  erosion  of  shores 36 

Surface-rock  underlying  drift 519 

Syenite 203 

Syncline 178 

Syringopora  verticillata 306 


Table  mountains  of  Cumberland  plateau 267 

Table-rocks 13 

Tallulah  River  Gorge 18 

Tachylite 207 

Taeniopteris  elegans 459 

Tail-fin,  heterocercal 341 

homocercal 341 

Talcose  schist 220 

Talus 8 

Tapirus  Tndicus 523 


INDEX. 


639 


Taylor 

Teleosaurus  brevidens 

Teleosts,  Cretaceous 

Terebratula  digona 

flavescens 

—  sphaeroidalis 

Terrace  epoch S45* 

—  epoch  in  Europe 

Terraces,  river 

Tertiary  animals 

American  localities 

birds 

—  coal 

—  diatoms 

—  fishes 

—  insects 

—  mammals 

—  mammalian  fauna,  general  observations. 

—  period 

period,  general  observations 

—  period,  physical  geography. . . 

—  plants 

—  reptiles 

—  rocks,  area  in  the  United  States 

—  rocks,  character 

—  subdivisions 

—  times,  map  of  United  States  in 

Tetragonolepis 

Textularia  variabilis 162, 

Theca  Davidii — 

Theriodonts 

Theropody 

Thin-crust  theory  of  earth. 

Thomassy " .* 

Thomson,  J 

--,W 

Thylacoleo  carnifex 

Tides,  effect 

Tiger,  saber-toothed 

Tillodontia 

Time,  geological  divisions  and  subdivisions. 

involved  in  the  Quaternary  period 

since  man  appeared 

geological,  estimate 

Tinoceras  ingens 

Titanotherlum 

Tooth,  ganoid,  structure 

Torreya 

Trachyte 

Transition  period 

Transportation  of  sediments 

by  glaciers 

Transporting  power  of  waves 

Trap 

Travertine 

Tree-fern,  living 

Tree-ferns  of  Coal  period  ...   

Trees,  erect  fossil,  in  coal-measures 

Trematosaurus 

Trenton  period 

Triassic  conifers  and  cycads 

fishes 

mammals 

period 


606 
D :  ' 
518 

.Ml 
v.'J 

588 

548 

51  •  i 
501 
519 
508 
508 

188 

m 

BOO 

I!'.* 

MM 

M 

88 

66 
87 

see 

85 
677 
58 1 

m 

598 

618 

276 

533 

588 

342 

£61 

207 

409 

18 

57 

88 

206 

78 


Triaesic  period,  subdivisions 415 

—  reptiles 417 

Triceratops  flabellatus 499 

Triconodon 448 

Trigonia  clavellata 429 

—  longa,  shell  and  cast 194 

—  pandicosta 460 

Trigonocarpon,  or  Trigonocarpus 360 

Trilobite,  larva 324 

Trilobites,  affinities  of 325 

Devonian 333 

Silurian  320 

Trinucleus  Pongerardi 323 

Trocholites  Ammonius 320 

Tuditanus  radiatus 404 

Tufa 91 

Turritella  alveata 512 

Turrulites  catenatus 482 

Tylosaurus  micromus 487 

dyspelor 487 

Tyndall 64,65,69,  186 

Tyndall's  theory  of  Glaciers 63 


U 

Uintah  basin 503 

Uintatherium 532 

Umbrella  planulata 512 

Unconformity 179 

between  Silurian  and  Laurentian 294 

Underclay  of  coal-seam 347 

Ungulates,  diferentiation  of  families 540 

Unio  Holmesianus 498 

Univalves,  Silurian 316 

Urodela 400 

Ursus  amplidens 588 

—  pristinua 582 

spehcus 577 


374 

418 
296 
415 
416 
421 
415 


Vanessa  Pluro 

Vein-stuffs 

Veins,  age  how  determined 

—  auriferous  quartz 

auriferous,  of  California 

—  cupriferous 

fissure 

metalliferous 

metalliferous,  contents 

metalliferous,  important  laws  affecting 

metalliferous,  ribboned  structure 

metalliferous,  theory 

metalliferous,  vein-stuffs  

mineral 

mineral,  characteristics 

fissure,  irregularities 

of  infiltration 

of  segregation 

—  plumbiferous 

—  pockets  in 

surface-changes 

Vegetable  accumulations 

Ventriculites  simplex 


515 


240 
247 


241 
236 
243 


237 
224 


240 
08 


140 
477 


640 


INDEX. 


PAGE 

Venus  pertennis 513 

Vespa  avatina 514 

Vesuvius,  section 95 

Viburnum  Newberrianum 497 

Viscosity  theory  of  glaciers,  Forbes's 61 

Viviparus  trochiformis 498 

Volcanic  cone,  comparison  with  exogenous 

tree 96 

—  cone,  formation 93 

cones,  kinds 93 

Volcanic  conglomerate 214 

—  phenomena,  subordinate 101 

—  rocks,  decay 7 

—  rocks,  mineral   composition   and   sub- 
groups    207 

Volcanoes,  aqueo- igneous  theory 100 

chemical  theory 99 

definition 87 

estimate  of  age 97 

—  internal  fluidity  theory 98 

—  mechanical  theory 100 

size,  number,  and  distribution 88 

—  superheated  gas  theory 100 

theory 97 

Volutalithes  dumosa 512 

symmetrica 512 

Voltzia  heterophylla 415 

Von  Cotta...                                                   ..  204 


W 

Wahsatch  beds 530 

range 259,  266 

Walchia  diffusus 457 

—  piniformis 412 

Walcott 299 

Wallace 277,  473 

modification  of  CrolPs  theory  of  climate  592 

Ward 358,  475,  497 

Water,  chemical  agencies 74 

mechanical  agencies 9 

comparison  of  different  forms 73 


PAGE 

Waterfalls 12 

Water-shed 10 

Waters,  subterranean 74 

Waves,  erosion  by 34 

—  transporting  power  of 38 

—  and  tides,  examples  of  action 35 

Wealden 424 

Weed 161 

Wells,  artesian 75 

White 299,  497 

White  River  Basin 535 

Whitney 257,  469,  473 

Williamson 367,  369 

Williston 439 

Winchell,  A 15 

Winding  course  of  rivers 23 

Winds,  action 8 

Wood,  petrified 191 

Worm,  marine  trail 321 

Worms,  tracks  and  borings,  Silurian 320 

Worm-teeth...  .;  321 


Xilocopa  senilis. 


..  514 


Yellowstone  Park,  springs  in 79 

—  geysers  of 103 

Yosemite,  falls  of 15 


Zacanthoides  typicalis .Jr. . .  299 

Zamia  spiralis yf.  -X. .  426 

Zamites  occidentalis f. 459 

Zaphrentis  bilateralis 306 

Wortheni 331 

Zeacrinus  elegans 393 

Zeuglodon  cetoides 528 

Zylobius  sigillarise 397 


THE   END. 


RETURN  TO  the  circulation  desk  of  any 
University  of  California  Library 

or  to  the 

NORTHERN  REGIONAL  LIBRARY  FACILITY 
Bldg.  400,  Richmond  Field  Station 
University  of  California 
Richmond,  CA  94804-4698 

ALL  BOOKS  MAY  BE  RECALLED  AFTER  7  DAYS 

•  2-month  loans  may  be  renewed  by  calling 
(510)642-6753 

•  1-year  loans  may  be  recharged  by  bringing 
books  to  NRLF 

•  Renewals  and  recharges  may  be  made 
4  days  prior  to  due  date 

DUE  AS  STAMPED  BELOW 
2005 


DD20   12  M   1-05 


15098 


r.XIYKUSITY  OF  CALIFORNIA  LIBRARY 


